UNIVERSITI PUTRA MALAYSIA MECHANICAL …
45
UNIVERSITI PUTRA MALAYSIA MECHANICAL CHARACTERIZATION OF AA6061-T6 ALUMINUM ALLOY FRICTION STIR AND TUNGSTEN ARC WELDED WITH AND WITHOUT POST-WELD HEAT TREATMENT FIROUZ FADAEIFARD ITMA 2016 16
Transcript of UNIVERSITI PUTRA MALAYSIA MECHANICAL …
UNIVERSITI PUTRA MALAYSIA
MECHANICAL CHARACTERIZATION OF AA6061-T6 ALUMINUM ALLOY FRICTION STIR AND TUNGSTEN ARC WELDED WITH AND WITHOUT
POST-WELD HEAT TREATMENT
FIROUZ FADAEIFARD
ITMA 2016 16
© COPYRIG
HT UPM
MECHANICAL CHARACTERIZATION OF AA6061-T6 ALUMINUM ALLOY FRICTION STIR AND TUNGSTEN ARC WELDED WITH AND WITHOUT
POST-WELD HEAT TREATMENT
By
FIROUZ FADAEIFARD
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfillment of the Requirements for the Degree of Doctor of Philosophy
December 2016
© COPYRIG
HT UPM
© COPYRIG
HT UPM
COPYRIGHT
All materials contained within the thesis, including without limitation text, logos, icons, photographs, and all other works, is copyright material of universiti Putra Malaysia, otherwise stated. Use may be made of any material contained within the thesis for non-commercial purposes from the copyright holder. Commercial use of material may only on be made with the express, prior, written permission of Universiti Putra Malaysia.
Copyright© Universiti Putra Malaysia
© COPYRIG
HT UPM
TO
My parents My wife My children My brothers and sisters My nieces and nephews
© COPYRIG
HT UPM
i
Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfillment of the requirement for the degree of Doctor of Philosophy
MECHANICAL CHARACTERIZATION OF AA6061-T6 ALUMINUM ALLOY FRICTION STIR AND TUNGSTEN ARC WELDED WITH AND WITHOUT
POST-WELD HEAT TREATMENT
By
FIROUZ FADAEIFARD
December 2016
Chairman: Associate Prof. Khamirul Amin Matori, PhD Faculty : Institute of Advanced Technology
Friction stir welding (FSW) process is a solid-state method in which is accepted as a favorable joining method for aluminum alloys and other engineering materials. The joining of metal plates in FSW is done at below their melting point temperature and based on a thermo-mechanical action used by a non-consumable welding tool onto metal plates. Despite the fast development in solid state welding, fusing welding such as Tungsten Inert Gas welding (TIG) is still vastly applied for thick joint design. Furthermore, solid state joining such as FSW is not applicable for positions such as overhead, horizontal and vertical. On the other hand, aluminum alloys have been increasingly applied in different industries, therefore, several research works on the manufacturing processes of these alloys have been developed over the time such as joining (welding) processes. The 6061-T6 aluminum alloy is an Al-Mg-Si precipitation hardening alloy from the 6XXX series which is often employed because it presents relatively good mechanical properties in relation to its light weight. Since the microstructure of 6061-T6 aluminium alloy and chemistry as well as dimension and distribution of the intermetallic particles in the matrix of aluminium alloy may be changed owing to heat generated and severe plastic deformation during the welding process. Accordingly, mechanical properties of weldments can be changed after welding as opposed to the base metal. However, the vast part of these changing can be recovered by doing post weld heat treatment (PWHT).
Butt joints of 6061-T6 aluminum alloy were produced by FSW, and the influence of process parameters on their welds quality of weldments in terms of welding defects, microstructure, hardness distribution, and tensile properties by applying the shoulder angle and welding speed in the range of 0-10° and 63-110 mm/min, respectively, have been investigated using NDT, optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive x-ray (EDX) facilities, XRD, Electron backscatter diffraction (EBSD) and mechanical test such as microhardness test and the tensile test on the welded joints, as the first and second objective. The welding results obtained shown that among all the welding conditions, two welding parameters which is 10°– 89 mm/min and 10°-110 mm/min showed the highest tensile properties (184 MPa for UTS) and higher hardness. Consequently, one of them selected to perform post weld heat treatment (PWHT). In additional to above mentioned characterization, nanoindentation
© COPYRIG
HT UPM
ii
test was done to find local mechanical and nanomechanical properties in as-weld and PWHT of selected sample (as stated in third objective). The majority of properties were closed to the base metal condition by performing PWHT.
The TIG welding process was performed on 60061-T6 aluminum alloy using ER5356 filler. All above mentioned characterization was performed to find mechanical and nanomechanical properties in as-weld and PWHT conditions. PWHT led to microstructural recovery of the Heat Affected Zone (HAZ) in addition to the appearance of β-phase (Al3Mg2) in the grain boundaries of weld zone. The ultimate tensile stress was improved to 204 MPa, even though the improvement in FSW sample (after PWHT) was better with almost 300 MPa.
Final comparison between the effect of these two process on mechanical, metallurgical and nanomechanical properties of 6061-T6 aluminum alloy as well as the effect of PWHT in the properties studied shows better mechanical, metallurgical and metallurgical properties.
© COPYRIG
HT UPM
iii
Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Doktor Falsafah
PENCIRIAN MEKANIKAL BAGI AA6061-T6 ALUMINIUM ALOI KIMPALAN KACAU GESERAN DAN TUNGSTEN ARKA DENGAN DAN
TANPA RAWATAN HABA SELEPAS KIMPALAN
Oleh
FIROUZ FADAEIFARD
Disember 2016
Pengerusi: Prof. Madya Khamirul Amin Matori, PhD Fakulti: Institute Teknologi Maju
Proses kimpalan kacau geseran (FSW) adalah satu kaedah keadaan pepejal yang diterima sebagai satu kaedah yang baik untuk kaedah penyambungan bagi aluminium aloi dan bahan-bahan kejuruteraan yang lain. Penyambungan plat logam menggunakan FSW dilakukan di bawah suhu takat lebur dan berdasarkan tindakan mekanikal-haba yang dihasilkan oleh alat kimpalan ke atas plat logam. Walaupun pembangunan yang pesat dalam kimpalan keadaan pepejal, kimpalan leburan seperti kimpalan Tungsten Gas Lengai (TIG) masih banyak digunakan bagi penyambungan bereka-bentuk tebal. Tambahan pula, penyambungan keadaan pepejal seperti FSW tidak boleh digunakan untuk kedudukan seperti hujung, mendatar dan menegak. Sebaliknya, aluminium aloi semakin digunakan dalam industri yang berbeza, oleh itu, beberapa kerja penyelidikan mengenai proses pembuatan aloi ini telah dibangunkan dari masa ke masa seperti proses penyambungan (pengimpalan). Aluminium aloi 6061-T6 adalah aloi pemendakan pengerasan bagi Al-Mg-Si dari siri 6XXX yang sering digunakan, kerana ia mempunyai sifat-sifat mekanik yang baik jika dibandingkan dengan beratnya yang ringan. Disebabkan mikrostruktur 6061-T6 aluminium aloi dan sifat kimianya, serta dimensi dan pengagihan zarah antara-logam dalam matriks aluminium aloi boleh diubah kerana haba yang dihasilkan dan ubah bentuk plastik yang besar semasa proses kimpalan berlaku. Oleh itu, sifat-sifat mekanikal hasil kimpalan boleh diubah selepas kimpalan dibandingkan dengan logam asal. Walau bagaimanapun, sebahagian besar perubahan ini boleh diperolehi semula dengan melakukan rawatan haba selepas kimpalan (PWHT).
Penyambungan bahagian hujung 6061-T6 aluminium aloi telah dihasilkan menggunakan FSW, dan pengaruh proses parameter kepada kualiti kimpalan bagi hasil kimpalan dari segi kecacatan kimpalan, mikrostruktur, taburan kekerasan, dan sifat-sifat tegangan terhadap sudut bahu dan kelajuan kimpalan masing-masing dalam julat 0-10° dan 63-110 mm/min telah dikaji dengan menggunakan NDT, mikroskop optik, imbasan mikroskop elektron (SEM) yang dilengkapi dengan kemudahan tenaga serakan x-ray (EDX), XRD, pembelauan pancaran balik elektron (EBSD) dan ujian mekanikal seperti ujian kekerasan-mikro dan ujian tegangan pada sambungan kimpalan, seperti yang dinyatakan dalam objektif pertama dan kedua. Hasil kimpalan yang diperolehi menunjukkan bahawa di antara semua keadaan kimpalan, dua parameter kimpalan iaitu
© COPYRIG
HT UPM
iv
10°-89 mm/min dan 10°-110 mm/min menunjukkan sifat tegangan yang paling tinggi (184 MPa untuk UTS) serta kekerasan yang lebih tinggi. Oleh itu, salah satu parametertelah dipilih untuk dilakukan proses rawatan haba selepas kimpalan (PWHT). Tambahan kepada pencirian yang dinyatakan di atas, ujian nano-indentasi telah dilakukan untuk mencari sifat-sifat mekanik dan nano-mekanikal setempat dalam sampel kimpalan dan PWHT yang dipilih (seperti yang dinyatakan di objektif ketiga). Majoriti ciri-ciri yang diperolehi adalah hampir kepada keadaan logam asal selepas PWHT dilakukan.
Proses kimpalan TIG telah dilakukan ke atas aluminium aloi 60061-T6 dengan menggunakan pengisi ER5356. Semua pencirian yang disebut di atas telah dilakukan untuk mencari sifat-sifat mekanik dan nano-mekanikal dalam kimpalan dan keadaan PWHT. PWHT menunjukkan kepada pemulihan mikrostruktur di zon yang terjejas haba (HAZ) sebagai tambahan kepada kemunculan β-fasa (Al3Mg2) di sempadan butiran bagi zon kimpalan. Tegasan tegangan muktamad telah meningkat kepada 204 MPa, walaupun peningkatan di dalam sampel FSW (selepas PWHT) lebih baik dengan hampir 300 MPa. Perbandingan akhir kesan di antara kedua-dua proses pada sifat-sifat mekanik, pelogaman dan nano-mekanikal 6061-T6 aluminium aloi serta kesan PWHT dalam sifat-sifat yang dikaji menunjukkan sifat mekanikal, pelogaman dan nono-mekanikal lebih baik.
© COPYRIG
HT UPM
v
ACKNOWLEDGEMENTS
I would like to express my gratitude and sincere respect to my supervisor Associate Prof. Dr. Khamirul Amin Matori for his guidance and support throughout my research.
I would also like to thank my co-supervisors Professor Dr. Sidek Abd Aziz, andProfessor. Dr. Mohd Khairol Anuar b. Mohd Ariffin for providing useful suggestions for the completion of this research.
I would like to thank Professor Dr. Didier Chicot for his valuable support.
I would like to give my sincere thankfulness to my wife (Farzaneh) and my children (Amir Masoud and Amir Behnoud) for their patient and support.
Special thanks to my friend Ahmad Masoumzadeh for his valuable supports.
© COPYRIG
HT UPM
vi
I certify that an Examination Committee met on 4 December 2016 to conduct the final examination of Firouz Fadaeifard on his thesis entitled “Mechanical Characterization of A6061-T6 Aluminum Alloy Friction Stir and Tungsten Arc Welded with and without Post-Weld Heat Treatment” in accordance with the Universities and University Colleges Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U. (A) 106] 15 march 1998. The Committee recommends that the student be awarded the Doctor of Philosophy.
Member of the Thesis Examination Committee were as follows:
Mohd Nizar Hamidon, PhD Associate professor Faculty of Enginnering Universiti Putra Malaysia (Chairman)
Shamsuddin bin Sulaiman , PhD Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)
Faizal bin Mustapha, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)
Ali Hussein Ataiwi Al Omairy, PhD Professor Materials Engineering Department Kufa University Iraq (External Examiner)
NOR AINI AB. SHUKOR, PhD Professor and Deputy Dean
School of Graduate Studies Universiti Putra Malaysia
Date: 28 February 2017
© COPYRIG
HT UPM
vii
This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfillment of the requirements for the degree of Doctor of Philosophy. The members of the Supervisory Committee were as follows:
Khamirul Amin Matori , PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman)
Sidek Abd Aziz , PhD Professor
Faculty of Science Universiti Putra Malaysia (Member)
Mohd Khairol Anuar b. Mohd Ariffin , PhD Professor, Ir
Faculty of Engineering Universiti Putra Malaysia (Member)
ROBIAH BINTI YUNUS, PhD Professor and Dean
School of Graduate Studies Universiti Putra Malaysia
Date:
© COPYRIG
HT UPM
viii
Declaration by Graduate Student
I hereby confirm that: � this thesis is my original work; � quotations, illustrations and citations have been duly referenced; � this thesis has not been submitted previously or concurrently for any other degree at
any other institutions; � intellectual property from the thesis and copyright of thesis are fully-owned by
Universiti Putra Malaysia, as according to the Universiti Putra Malaysia (Research) Rules 2012;
� written permission must be obtained from supervisor and the office of Deputy Vice-Chancellor (Research and Innovation) before thesis is published (in the form of written, printed or in electronic form) including books, journals, modules, proceedings, popular writings, seminar papers, manuscripts, posters, reports, lecture notes, learning modules or any other materials as stated in the Universiti Putra Malaysia (Research) Rules 2012;
� There is no plagiarism or data falsification/fabrication in the thesis, and scholarly integrity is upheld as according to the Universiti Putra Malaysia (Graduate Studies) Rules 2003 (Revision 2012-2013) and the Universiti Putra Malaysia (Research) Rules 2012. The thesis has undergone plagiarism detection software.
Signature: ------------------------------------------------ Date: --------------------------------
Name and Matric No.: Firouz Fadaeifard, GS39168
© COPYRIG
HT UPM
ix
Declaration by Members of Supervisory Committee
This is to confirm that: � the research conducted and the writing of this thesis was under our supervision; � Supervision responsibilities as stated in the Universiti Putra Malaysia (Graduate
Studies) Rules 2003 (Revision 2012-2013) are adhered to.
Signature:Name of Chairman of Supervisory Committee: Associate Prof. Dr. Khamirul Amin Matori
Signature:Name of Member of Supervisory Committee: Professor Dr. Sidek Abd Aziz
Signature:Name of Member of Supervisory Committee: Professor Dr. Mohd Khairol Anuar b. Mohd
Ariffin
© COPYRIG
HT UPM
x
TABLE OF CONTENTS
PageABSTRACT iABSTRAK iiiACKNOWLEDGEMENT ivAPPROVAL viDECLARATION viiLIST OF TABLES xiiiLIST OF FIGURES xivLIST OF ABBREVIATIONS xix
CHAPTER1 INTRODUCTION 1
1.1 Background 11.2 problem statement 11.3 Objectives 31.4 Research Scope and Significance 31.5 Thesis Layout 4
2 LITERATURE REVIEW 52.1 Aluminum and Its Alloys: An Overview 5
2.1.1 Introduction 52.1.2 Alloy Designation System 52.1.3 Temper Designation System 62.1.4 Microstructural and Metallurgical Properties 62.1.5 Effect of Alloy Elements 92.1.6 Weldability of Aluminum Alloys 102.1.7 AA6061 Aluminum Alloys 10
2.2 Friction Stir Welding (FSW) 162.2.1 Background 162.2.2 Principle of Operation 182.2.3 Friction Stir Welding parameters and related Variables 192.2.4 Tool 24
2.2.4.1 Shoulder (diameter and surface) 252.2.4.2 Pin (probe) geometry 28
2.2.5 Welding speed 312.2.6 Post weld heat treatment (PWHT) 312.2.7 Flaws and Failures in FSW 31
2.3 TIG welding of aluminium alloys 332.4 A comparison; TIG and FSW 352.5 Indentation 38
2.5.1 Background 382.5.2 Origin of indentation for measuring the hardness 392.5.3 Comparison of techniques and born of different
indenters and methods41
2.5.4 Microindentation (Microhardness) 442.5.5 Nanoindentation Testing 452.5.6 Indenter Types 482.5.7 Projected area 50
© COPYRIG
HT UPM
xi
2.5.8 Pile up and Sink in (Swell) 512.5.9 Nanoindentation in welding joints 53
2.6 Summary 55
3 METHODOLOGY 563.1 Introduction 563.2 Material Selection 583.3 Welding Preparation for FSW samples 58
3.3.1 Plate Preparation 583.3.2 FSW Machine and Clamping System 593.3.3 Welding Tool Preparation 613.3.4 Selection of Welding Conditions 63
3.4 Welding Preparation for TIG samples 643.5 Post Weld Heat Treatment (PWHT) 653.6 Inspection and Non-Destructive Test (NDT) 663.7 Macro- Structure Evaluation 66
3.7.1 Sample Preparation 663.8 Micro- Structure Evaluation 67
3.8.1 Sample Preparation for Optical Microscopy, SEM and FESEM
67
3.8.2 Sample Preparation for EBSD 673.8.3 Grain Size Measurements 67
3.9 Mechanical Properties Evaluation 683.9.1 Micro-Hardness Testing 683.9.2 Tensile Testing 693.6.3 Fracture Behavior Evaluation of Weldments 70
3.10 XRD 703.11 Nanoindentation 70
3.11.1 Equipment 703.11.2 Method 71
4 RESULT AND DISCUSSION 734.1 Friction Stir Welding (FSW) 73
4.1.1 Non-destructive Inspection 734.1.2 Macrostructure study 764.1.3 Microstructure evaluation 834.1.4 Precipitations 954.1.5 Hardness Evaluation 994.1.6 Tensile properties and fractography 1014.1.7 The highlights of FSW of AA6061-T6 in different welding speeds and different shoulder angles
105
4.2 PWHT of FSW sample 1064.2.1 Macro and Microstructure analysis 1064.2.2 Tensile test and fractography 1124.2.3 Indentation: Hardness and elastic modulus 1154.2.4 The highlights of PWHT of FSW 121
4.3 TIG welding (as-weld and PWHT) 1224.3.1 Macrostructure 1224.3.2 Microhardness 1234.3.3 Microstructure study 1254.3.4 Tensile test and fractography 131
© COPYRIG
HT UPM
xii
4.3.5 Nanoindentation 1334.3.6 The highlights of TIG welding in as-weld and PWHT 138
5 CONCLUSIONS AND RECOMMENDATIONS 1395.1 Friction stir welding of 6061-T6 aluminum alloy 1395.2 PWHT of FSW join of 6061-T6 aluminum alloy 1395.3 TIG welding of 6061-T6 (as-weld and PWHT) 1405.4 Comparison of FSW and TIG welding of AA6061-T6 1415.5 Recommendations and Future Study 141
REFERENCES 142APPENDICES 158BIO DATA OF STUDENT 164LIST OF PUBLICATIONS 165
© COPYRIG
HT UPM
xiii
LIST OF TABLES
Table Page
2.1 Aluminum Alloy Designation System [2]. 62.2 Property-Microstructure Relationships in Aluminum Alloys
[5].7
2.3 Typical composition for commercial aluminum alloys (wt %) [40].
11
2.4 Overview over some selected temper designations [47]. 122.5 Properties of AA6XXX alloys in annealed condition [51]. 152.6 Properties of AA6XXX alloys in T6 condition [51]. 152.7 Applications of AA6XXX Aluminum Alloys [54]. 162.8 Mechanical properties of investigated materials [113]. 363.1 Nominal composition of parent alloy used in the welding test. 583.2 Mechanical properties of the 6061-T6 aluminum alloy. 583.3 Summary of material types and workpiece dimensions. 583.4 Summary of dimensions of the tools used in FSW experiments. 613.5 Process Parameters for fabricating FSW joints at constant
rotation speed (1480rpm).64
3.6 Chemical composition of the filler metal (wt.%). 644.1 γ and β deviations for different welds. 784.2 Grain size of NZs and HAZs. 904.3 Average hardness of NZs and HAZs. 1004.4 Mechanical properties obtained by tensile tests for machined
(RS-LHZ) and As-weld (Kissing bond).102
4.5 Mechanical properties obtained by tensile tests. 1034.6 Average grain size in the different zones of weld joint in as-
weld and PWHT samples.111
4.7 Mechanical properties obtained by tensile tests. 1134.8 The results of tensile tests. 131
© COPYRIG
HT UPM
xiv
LIST OF FIGURES
Figure Page 2.1 Equilibrium Binary Solid Solubility As A Function of
Temperature For Alloying Elements Most Frequently Added to Aluminium [3].
8
2.2 Phase Diagram of A Hypothetical Alloy System Showing the Β Solvus And GP Zone Solvus. For Composition (A). ΔT1 is the Temperature Range for Solution Heat Treatment, and ΔT2
is the Temperature Range for Precipitation Heat Treatment [5].
8
2.3 Contributions from dissolved alloying elements in solid solution (A) and particles from precipitation hardening (B, C)[48].
13
2.4 Effect of artificial ageing and naturally ageing on the strength evolution in Al/Mg/Si alloys. Naturally ageing only allows GP-zones to form [50].
14
2.5 Friction Stir Weld in the butt configuration with important Friction Stir Welding terminology identified [62].
18
2.6 Schematic of a typical FSW Cross-Section (A) Parent Material.(B) Heat Affected Zone. (C) Thermal Mechanically Affected Zone. (D) Weld Nugget [13].
19
2.7 Metal flow zone developed during friction stir joining [83]. 242.8 Material flow during FSW a) horizontal b) vertical [86]. 252.9 The effect of shoulder diameter to the peak temperature [88]. 26
2.10 Different shoulder features a) scrolled b) knurled c) ridged d) grooved e) concentric circle [87].
27
2.11 A cross section of a concave shoulder. 272.12 Changing in temperature distribution influenced by shoulder
angle [90]. Temperature distribution at t = 2.7 s: a) α = 0° , b) α = 2° , c) α = 4° , d) α = 6°.
28
2.13 Cylindrical tool design [82, 84]. 292.14 Basic variants on the Whorl™ type probes [86]. 292.15 Triflute™ tool with frustum shaped probe with three flutes
[86].29
2.16 Schematic diagrams of tool pin-tip profiles: a-thread taper, b-triangular, c-square, d-three grooves, and e-conical platform [92].
30
2.17 Cross section of weld zone (appearance of wormhole in advancing side like void) [93].
31
2.18 Metallographic analysis of the weld zones and size evaluation of a kissing bond (KB). (a) Overview image of a weld nugget with adjacent zones. (b) Detail of the large KB flaw with a clear zig-zag shape revealed by etching in AA7475 [95].
32
2.19 Schematic diagram of Newton’s cradle arrangement used by Hodgkinson in the 1830s to investigate relative dynamic hardness of range of materials [121].
38
2.20 Indentation machine developed by Calvert and Johnson in 1850s [124].
39
© COPYRIG
HT UPM
xv
2.21 Schematic diagram of Middelberg’s knife indentation. technique for studying hardness of railway tyres [125].
40
2.22 Indentation hardness machine reported by Unwin in 1896 [126].
40
2.23 Schematic drawing of Knoop indentation [139]. 422.24 Comparison of Knoop (leftmost), Vickers (middle) and Brinell
(rightmost) indentations [139].43
2.25 Schematic diagram showing pile-up around cone indentation [141].
43
2.26 Diagrams of two diamond indenters, Vickers and Knoop [143].
45
2.27 Schematic Diagrams of nanoindentation [150]. 462.28 (a) A typical load–displacement curve and (b) the deformation
pattern of an elastic –plastic sample during and after indentation [152].
47
2.29 SEM images of the tips of (a) Berkovich, (b) Knoop, and (c)cube-corner indenters used for nanoindentation testing. The tip radius of a typical diamond pyramidal indenter is in the order of 100 nm [152].
49
2.30 Indentation parameters for (a) Spherical, (b) Conical, (c) Vickers, and (d) Berkovich indenters (not to scale) [152].
49
2.31 AFM image of the plastic impressions [155] remaining in the BCB material after indentation (height scale is 0 to 20 nm from black to white) [155].
50
2.32 Matlab-mesh surface plot of 40 mN indent in 750 nm Cu film [156].
51
2.33 Calculated indentation contact profiles for: (a) non-work hardening materials (η=0); (b) work-hardening materials (η=10σy) [158].
52
3.1 Methodology flow chart. 573.2 A vertical milling machine used for FSW experiments. 593.3 Schematic of joint configuration utilized in this research. 603.4 The real shape of fixture (clamping) used to restrain the plates
during FSW.60
3.5 The real shape of welding tool designed in this work. 623.6 Shoulder of this work (α = 10°). 633.7 Joint design and welding sequences. 643.8 The joint and TIG welding. 653.9 T6- heat treatment cycle performed on the FSW samples. 66
3.10 MATLAB plot of microhardness points on the cross section of specimens.
68
3.11 Micro-hardness testing machine. 693.12 Instron universal Testing machine used for tensile test. 693.13 Tensile samples. 703.14 Load-displacement (P-h) curve of base metal (AA6061-T6)
obtained by applying the indentation load of 2.5 mN.72
4.1 Surface appearance of welded joints (as-weld). 754.2 Phase Array of AA6061-T6 FSW sample (89 mm/min, α=5°) 764.3 Macrograph of friction stir butt welded joint. (a) Optical
observation of the macrostructure of the entire as-weld zone 77
© COPYRIG
HT UPM
xvi
and (b) Magnification of the NZ/TMAZ/HAZ delimiting zone by SEM.
4.4 Schematic of FSW and affected area by shoulder and pin used in this study.
78
4.5 Cross-section macrostructure of butt joint section AA6061-T6 Al alloy at different conditions.
79
4.6 Kissing bond a and b) Macrograph of kissing bond in root c and d) FESEM image of kissing bond e) EDX of oxide layer around kissing bond.
81
4.7 Liquid penetrant test from the behind of joints. 824.8 Grain orientation analyzed by EBSD for welded sample
(110mm/min, α=10°) a) NZ b) TMAZ c) HAZ.85
4.9 FESEM image of base metal AA6061-T6. 864.10 Optical images of HAZs of different welding condition. 874.11 Optical image of NZ and TMAZ (89mm/min, α=10°). 884.12 Grain orientation analyzed by EBSD of NZ and TMAZ
(89mm/min, α=10°).88
4.13 Optical microstructure of NZ in highest and lowest welding speed of each shoulder angle.
89
4.14 Variation of average grain size in weld nugget zone (NZ) with welding speed.
91
4.15 Variation of average grain size in HAZs with welding speed. 914.16 EBSD image of different shoulder angle (α=0° and α=10°). 934.17 The figure poles of NZs in Figure 4.16. 944.18 SEM micrographs of intermetallic precipitates a) base metal
b) HAZ.95
4.19 EDXs of dark and white particles. 964.20 SEM micrographs of NZ different welding parameters. 974.21 XRD in different parts of FSW weldments AA6061-T6. 984.22 Distribution of Al0.7Fe3Si0.3 in TMAZ. 984.23 Hardness mapping in a) 110 mm/min, α=5° b) 110 mm/min,
α=5°.99
4.24 Hardness mapping in a) 110 mm/min, α=10° b) 110 mm/min, α=0°.
100
4.25 Fracture location. 1014.26 Tensile test graph for two different shoulder angles (0 and 10)
and two different welding speeds (63 mm/min and 110 mm/min).
102
4.27 FE-SEM image from kissing bond location. 1044.28 FE-SEM image from RS-LHZ location. 1054.29 Macrograph of friction stir butt welded joint (110 mm/min
welding speed and 80° shoulder angle).106
4.30 Macrograph of PWHT weldment. 1074.31 Observation of the grain boundaries by electron backscatter
diffraction (EBSD) of a) the Nugget Zone (NZ), b) the Thermo-Mechanically Affected Zone (TMAZ) and c) the Heat Affected Zone (HAZ).
107
4.32 Observation of the grain boundaries by electron backscatter diffraction (EBSD) after PWHT treatment of a) the NZ and TMAZ zones, b) the TMAZ zone and c) the HAZ and TMAZ zones.
108
© COPYRIG
HT UPM
xvii
4.33 Scanning electron microscopy images of HAZ zone for the a) As-weld and b) After PWHT samples.
109
4.34 Precipitates of Mg2Si (point B) and of Al0.7Fe3Si0.3 (point A) in the HAZ zone of the as-weld sample.
109
4.35 Grain orientation analyzed by EBSD performed in the NZ and TMAZ zones of the as-weld sample and its corresponding boundary map.
110
4.36 Grain orientation visible by EBSD performed in the NZ and TMAZ zone of the PWHT sample and its corresponding boundary map.
111
4.37 Tensile strength graph for as-weld and PWHT sample (AA6061-T6 FSW).
113
4.38 Fracture morphology by SEM observations of (a-b) as-weld joint (c-d) PWHT sample.
114
4.39 Hardness mapping in a) the as-weld joint and b) after the PWHT treatment.
115
4.40 Load-displacement (P-h) curves related to the NZ zone (a) and the TMAZ zone (b) compared to the base metal before and after the PWHT treatment.
117
4.41 Pile-up observed in the TMAZ zone of retreating side in the as-weld sample.
118
4.42 Contact area versus the contact indenter displacement including all the nanoindentation tests.
119
4.43 Distribution of Martens hardness (a) and elastic modulus (b) as a function of the distance through the whole welding zone in a perpendicular section obtained from instrumented indentation tests performed on the as-weld joint and after the PWHT treatment.
120
4.44 Macrograph of weldment in as-weld condition. 1124.45 Liquation cracking (LC). 1234.46 Distribution of microhardness (a) as-weld sample (b) after
PWHT.124
4.47 Microstructure of last pass (pass 4 from Figure 4.42) 1254.48 FE-SEM images of weld zone in as-weld sample (a) second
pass (b) first pass.126
4.49 EDS of points A in Figure 4.39-a. 1274.50 XRD of weld zone a) as-weld b) PWHT. 1274.51 FE-SEM microstructure of weld zone after PWHT (pass 1). 1284.52 Microstructure of first welding pass (a) as-weld (b) PWHT. 1284.53 FE-SEM image of HAZ in as weld sample (a) HAZ1 (b)
HAZ2.129
4.54 EBSD orientation image HAZs and their corresponding boundary map.
130
4.55 Tensile strength graph for as-weld and PWHT sample (AA6061-T6 TIG).
131
4.56 Fractograph of as-weld sample (a) low magnification (500X) (b) high magnification (2500X).
132
4.57 Fractograph of PWHT sample (a) low magnification (500X) (b) high magnification (2500X).
132
4.58 P-h curve of nanoindentation tests 134
© COPYRIG
HT UPM
xviii
4.59 HM (Hnano) profile (a) in weldment along line B of Figure 4.35 (as-weld and PWHT) (b) along welding passes (as-weld and PWHT).
135
4.60 Elastic modulus profile (a) in weldment along line B of Figure 4.35 (as-weld and PWHT) (b) along welding passes (as-weld and PWHT).
137
4.61 Cross section of pile-up in HAZ2. 138
© COPYRIG
HT UPM
xix
LIST OF ABBREVIATIONS
FSW Friction stir weldingOM Optical MicroscopeSEM Scanning Electron MicroscopeAFM Atomic Force MicroscopyEDX Electron Depressive X-rayBM Base Metal (Parent Alloy)PWHT Post Weld Heat TreatmentHAZ Heat Affected ZoneTMAZ Thermo Mechanical Affected ZoneNZ Weld Nugget ZoneAS Advancing side of WNZRS Retreating side of WNZSZ Stir zoneHI Heat IndexUTS Ultimate tensile strength MPaω(Ω) Rotation Speed (rpm)υ Welding Speed (mm/min)α Shoulder AngleTWI The Welding Institute
© COPYRIG
HT UPM
© COPYRIG
HT UPM
1
CHAPTER 1
INTRODUCTION
1.1 Background
Aluminium has been existed and developed Since 115 years ago. American Charles Martin Hall, and a Frenchman Paul Heroult, independently, has developed a process allowing the economical production of aluminium by electrolysis from a fused salt bath in 1900st [1]. All favorable mechanical properties, acceptable corrosion resistance, light weight, appropriate weld-ability, and increased toughness make it more applicable. In recent years, aluminum alloys have become more popular in science and engineering fields according to its unique properties. Nowadays, Aluminum alloys have been increasingly applied in different industries; therefore, several research works in aluminum manufacturing have been developed like the joining processes. Welding, as a fabrication or maintenance process in aluminum alloys has been seen more in the researches of materials and metallurgy [1-5].
In modern industry, there are many different welding methods to join metals, ranging from the conventional oxyacetylene torch welding to laser welding. All types of welding can be divided in two common categories as fusion welding and solid state welding [6-8].
Heat is used in fusion welding processes with or without application of filler metal to unite two metals in molten state. Auxiliary materials such as shielding gas and flux may be used to make or ease the process possibility. Surface preparation is also required. Metal Inert Gas welding (MIG) and Tungsten Inert Gas welding (TIG) are two examples of the process [9-11]. The solid state welding, on the other hand, is the process where joining is produced at temperatures well below the melting temperature of base metal without any need for the filler material. Some examples of solid state welding are friction, explosion, hot pressure, ultrasonic and friction stir welding (FSW). The process has three important parameters: time, temperature and pressure. The last two, depending on the process, can be used individually or in combination to produce the joint [4-6].
1.2 Problem statement
Melting and solidification can cause several defects such as porosity and cracking, and, have negative effects on mechanical properties in both base and weld metal cited as an example of fusion welding disadvantages. However, FSW may possibly present extra potential for aluminum alloys since it can be performed without any toxic fumes, and without some welding defects that related to solidification. It means, since the base metal does not reach the melting point, defects like porosity normally coming from melting are not seen in this process. Moreover, base metals retain a majority of their original
© COPYRIG
HT UPM
2
properties in addition to the fact that the heat affected zone (HAZ) is very small in comparison with fusion welding techniques [12-14].
Despite the fast development in solid state welding, fusing welding such as TIG is unavoidable for thick joint design. Although recent progress in robotic FSW, it is not easily applicable for some welding positions such as overhead, horizontal and vertical. Furthermore, there are limitations in using of FSW for different joint design. However TIG welding is used for all welding position as well as all welding joint designs. The site application of TIG welding is another benefit of this process compare to FSW [4, 6].
The FSW process includes complex interactions among the process parameters, alloy properties, and tool geometry affecting the final mechanical properties and quality of the weld [12]. The investigations and new researches on the role of process parameters such as shoulder geometry and welding speed on the microstructural development, defect formation, precipitations’ role, mechanical properties and quality would be in demand. The proper choice of welding procedure and process parameters will lead to enhancement the mechanical and metallurgical properties [13]. Furthermore, there is no research in the effect of shoulder angle in mechanical properties of friction stir welded joint in heat treatable aluminum alloys.
On the other hand, there are many researches has been done in TIG welding as the most common fusion welding of heat treatable aluminum alloys by using 4-series aluminum alloys (such as ER4043) [6-8]. However, there is a few works by using ER5356 as a filler metal. Even there is no work to investigate precipitation and microstructure by using electron backscatter diffraction (EBSD) and nanoindentation for TIG welded joint.
Among Aluminum alloys, AA6061-T6 as an important heat treatable alloy, and widely used in many industries such as automotive, aerospace and shipbuilding due to good weld-ability, good corrosion resistance and appropriate mechanical properties [1-3, 5-8]. This material has seen in many applications for production such as Boeing’s Delta II and Delta IV Expendable Launch Vehicle, Lockheed Martin’s external tank for the space shuttle transportation system, and primary structures of ultra-lightweight jets like the Eclipse 500.
This widespread application of AA6061 in industries needs to be technically and scientifically supported by metallurgical and mechanical comparison between FSW and TIG processes. There are some works to evaluate and compare TIG and FSW in aluminum alloys [15, 16]. On the other hand, the local characterization as an effective evaluation, by using indentation and nanoindentation, has recently used in weldments [17]. The nanoindentation analysis can be applied for extract metallurgical and mechanical properties such as elastic modulus and hardness indentation [18]. However, this characterization has not applied yet to compare TIG and FSW in AA6061.
Post weld heat treatment (PWHT) has used to recover mechanical properties after welding. There are many attempts to investigate FSW joint by performing PWHT [19-
© COPYRIG
HT UPM
3
22] however, there is lack of knowledge about this comparison and evaluation after PWHT on as-weld samples of these 2 methods (TIG and FSW) and their related joints.
1.3 Objectives
The overall goal of this study is the new attempt to compare mechanical and metallurgical properties of AA6061-T6 TIG and FSW welded joints. The effect of PWHT on these properties are investigated for both welding process as well. It is expected that the goal of this research is to be achieved through the following objectives:
1. To characterize the mechanical and metallurgical properties of friction stir welded joints in different parameters.
2. To find the mechanical and metallurgical properties of selected sample among FSW weldments in as-weld and PWHT conditions.
3. To study the mechanical and metallurgical properties of TIG welded joints in as-weld and PWHT conditions.
4. To compare the metallurgical and mechanical properties of TIG and FSW welded joints.
1.4 Research Scope and Significance
Since there are different methods of welding, and each method includes different parameters, techniques, materials, thickness limitation and post processing. These varieties can consequence a complicated problem. Some scopes have been considered to execute this research.
1. This research is done for TIG welding and FSW. 2. The joint design is butt joint. 3. It is limited to welding 9.6 mm thick AA6061-T6 aluminum alloys for both
welding process. 4. The shielding gas in TIG welding is Argon. 5. The variables of FSW are limited to welding speed (less than 110 mm/min) and
shoulder angle (0º to 10º). 6. The post weld heat treatment is T6 that has done in less than 5 days after
welding.
It needs to be said that the investigation and comparison of these two processes in mechanical characterization are limited to tensile test, microhardness and nanoindentation. Whereas the metallurgical properties are studied by using XRD, optical microscopy, SEM, FESEM and EBSD.
© COPYRIG
HT UPM
4
1.5 Thesis Layout
This thesis is organized into 5 chapters. Brief descriptions of the contents of each chapter are given as follows:
1. Chapter 1 includes a brief background, problem statements, objectives, limitations and scopes of this research.
2. Chapter 2 presents a literature review; including aluminum alloys, friction stir welding, TIG welding and indentation.
3. Chapter 3 describes the materials and research methodology used in the study including research design, experimental work, pin and shoulder, characterization method and mathematical formula of nanoindentation..
4. The results and data of FSW, PWHT of FSW sample, TIG and PWHT of TIG weldment are presented in chapter 4.
5. Chapter 5 concludes the findings of FSW and TIG, comparison and recommendation of possible future works.
© COPYRIG
HT UPM
142
REFERENCES
[1] D. Altenpohl, 1982, 'Aluminium Viewed From Within', Aluminium-Verlag, Dusseldorf, West Germany.
[2] "Aluminium Standards and Data", Eighth Edition, 1984, the Aluminium Association Inc. New York.
[3] ASM Specialty Handbook, 1993, "Aluminium and Aluminium Alloys", J. R. Davis and Davis & Associates. Editors. ASM International. Materials Park. OH.
[4] J. K. Solberg, 2009, "Teknologiske metaller og legeringer", Institutt for material teknologi, Norwegian University of Science and Technology, NTNU, pp. 215-217.
[5] C. P. Blakenship. Jr. E. A. Starke, and E. Hombogen, 1996, "In Microstructure and Properties of Materials", p. 1, J. C. M. Li. Editor, World Scientific. Singapore
[6] I. Török, K. Juhász, Á. Meilinger and A. Balogh, 2012, "Main Characteristics of Fusion and Pressure Welding of Aluminium Alloys", Journal of Production Processes and Systems, 6 (1), pp. 91-106.
[7] R. Ilyushenko and V. Nesterenkov, 2006, "Novel Technique for Joining of Thick Section Difficult-to-Weld Aluminium Alloys", Materials Science Forum, 519-521, pp. 1125-1130.
[8] G. Mathers, 2002, "The Welding of Aluminium and Its Alloys", Published by Wood head Publishing Limited Ltd, UK.
[9] R. Ambriz, G. Barrera, R. García, and V.H. López, 2010, “The microstructure and mechanical strength of Al-6061-T6 GMA welds obtained with the modified indirect electric arc joint”, Materials & Design, 31, pp. 2978-2986.
[10] A. Kumar and S. Sundarrajan, 2009, “Effect of welding parameters on mechanical properties and optimization of pulsed TIG welding of Al-Mg-Sialloy”, The International Journal of Advanced Manufacturing Technology, 42, pp.118- 125.
[11] R. Ambriz, G. Barrera, R. García and V.H. López, 2010, “Effect of the weld thermal cycles of the modified indirect electric arc on the mechanical properties of the AA6061-T6 alloy”, Welding International, 24, pp. 321-328 .
[12] T. Ole. Midling, E. J. Morley and A. Sandvik, 1996, "Friction stir welding", The Welding Institute, UK, Assignee, Patent 5813592.
[13] R.S. Mishra and Z.Y. Ma, 2005, "Friction Stir welding and processing", Materials Science and Engineering R, 50, pp.1- 78.
[14] J. He, Z. Ling, and H. Li, 2015, “Effect of tool rotational speed on residual stress, microstructure, and tensile properties of friction stir welded 6061-T6 aluminum alloy thick plate”, The International Journal of Advanced Manufacturing Technology, pp.1-9.
© COPYRIG
HT UPM
143
[15] H. E. Zhen-bo, Y. Y. Peng, Z.M. Yin,and X.F. Lei, 2011, “Comparison of FSW and TIG welded joints in Al-Mg-Mn-Sc-Zr alloy plates” , Transactions of Nonferrous Metals Society of China, 21, pp. 1685-1691.
[16] Taban, E. and Kaluc, E., 2007. Comparison between microstructure characteristics and joint performance of 5086-H32 aluminium alloy welded by MIG, TIG and friction stir welding processes. Kovove Materialy, 45(5), pp.241-249.
[17] Kim, J.W., Lee, K., Kim, J.S. and Byun, T.S., 2009, “Local mechanical properties of Alloy 82/182 dissimilar weld joint between SA508 Gr. 1a and F316 SS at RT and 320 C”. Journal of Nuclear Materials, 384(3), pp.212-221.
[18] Pantelis, D.I., Karakizis, P.N., Daniolos, N.M., Charitidis, C.A., Koumoulos, E.P. and Dragatogiannis, D.A., 2016, “Microstructural study and mechanical properties of dissimilar friction stir welded AA5083-H111 and AA6082-T6 reinforced with SiC nanoparticles”, Materials and Manufacturing Processes,31(3), pp.264-274.
[19] Hu, Z., Yuan, S., Wang, X., Liu, G. and Huang, Y., 2011, “Effect of post-weld heat treatment on the microstructure and plastic deformation behavior of friction stir welded 2024”, Materials & Design, 32(10), pp.5055-5060.
[20] Z. Nikseresht, F. Karimzadeh, M.A. Golozar, and M. Heidarbeigy, 2010, “Effect of heat treatment on microstructure and corrosion behavior of Al6061 alloy weldment”, Materials & Design, 31, pp. 2643-2648.
[21] K.N. Krishnan, 2002, “The effect of post weld heat treatment on the properties of 6061 friction stir welded joints”, Journal of Material Science, 37, pp. 473–480.
[22] K. Elangovan and V. Balasubramanian, 2008, “Influences of post-weld heat treatment on tensile properties of friction stir-welded AA6061 aluminum alloy joints”, Material Characterization, 59, pp. 1168-1177.
[23] G. Lucas, 1996, “Aluminum structural applications”, Advanced Materials Processing, 149, pp. 29-30.
[24] A. Al-Rawajfeh and S. Al Qawabah, 2009, "Investigation of Copper Addition on the Mechanical Properties and Corrosion Resistance of Commercially Pure", Emirates Journal for Engineering Research, 14 (1), pp. 47-52.
[25] S. Court, K. Gatenby and D. Lloyd, 2001, "Factors Affecting the Strength and Formability of Alloys based on Al-3 wt% Mg", Materials Science and Engineering A, 319-321, pp. 443- 447.
[26] J. R. Davis, 1999,"Corrosion of Aluminium and its Alloys", Published by ASM International, USA
[27] C. Vargel, 2004, "Corrosion of Aluminium", Published by Elsevier, France.
[28] V. Ocenasek and M. Slamova, 2001, "Resistance to Recrystallization Due to Sc and Zr Addition to Al–Mg Alloys", Material Characterization, 47, pp. 157-162.
© COPYRIG
HT UPM
144
[29] I. Török, K. Juhász, Á. Meilinger and A. Balogh, 2012, "Main Characteristics of Fusion and Pressure Welding of Aluminium Alloys", Journal of Production Processes and Systems, 6 (1), pp. 91-106.
[30] R. Ilyushenko and V. Nesterenkov, 2006, "Novel Technique for Joining of Thick Section Difficult-to-Weld Aluminium Alloys", Materials Science Forum, 519-521, pp. 1125-1130.
[31] G. Mathers, 2002, "The Welding of Aluminium and Its Alloys", Published by Wood head Publishing Limited Ltd, UK.
[32] W. Hufnagel, 1999, "Key to Aluminium Alloys", Aluminium Publication, Dusseldorf, Germany.
[33] T. R. Ramachandran, 2006, "Advances in Aluminium Processing and Its Automotive Application", Workshop Lecture Notes, pp. 28-32, Indian Institute of Metals, Pune Chapter.
[34] G. Dieter, 1988, "Mechanical Metallurgy", SI Metric Edition, McGraw-Hill, London, UK.
[35] 2010, 'Alloy Composition Details', http://aluminium.matter.org.uk/aluselect/06 composition browse.asp.
[36] D. Kopeliovich, 2010, "Wrought aluminium-magnesium-silicon alloys (6XXX), http://www.substech.com/dokuwiki/doku.php?id=wrough.aluminium magnesium-silicon alloys 6XXX.
[37] 2010, The Aluminium Association, ' Technical FAQs & Information', http://www.aluminum.org/resources/technical-faqs-information
[38] G. Gottstein, 2004, "Physical Foundations of Materials Science", Springer, Berlin, Germany.
[39] M. H. Larsen, 2010, "Effect of Composition and Thermo-Mechanical Processing on the Intergranular Corrosion of AA6000 Aluminium Alloys", Norwegian University of Science and Technology, NTNU.
[40] H. Zhan, J. M. C. Mol, F. Hannour, L. Zhuang, H. Terryn and J. H. W. de Wit, 2008, "The Influence of Copper Content on Intergranular Corrosion of Model AlMgSi(Cu) Alloys", Materials and Corrosion, 59 (8), pp.670-675.
[41] P. Mukhopadhyay, 2012, "Alloy Designation, Processing, and Use of AA6XXX Series Aluminium Alloys", International Scholarly Research Network, ISRN Metallurgy, Article ID 165082, pp. 1-15.
[42] A. Simar, Y. Bréchet, B. de Meester, A. Denquin, C. Gallais and T. Pardoen, 2012, "Integrated Modelling of Friction Stir Welding of 6XXX Series Al Alloys: Process, Microstructure and Properties", Progress in Materials Science, 57, pp. 95-183.
[43] A.K. Gupta and D.J. Lloyd, 1992, "The Precipitation in a Super Purity Al–Mg–Si Alloy", In: 3rd International. Conference of. Aluminium Alloys, Trondheim, Norway.
© COPYRIG
HT UPM
145
[44] A.K. Gupta, D.J. Lloyd and S.A. Court, 2001, "Precipitation Hardening Processes in an Al-0.4% Mg-1.3% Si-0.25% Fe Aluminum Alloy", Materials Science and Engineering A, 301, pp.140-146.
[45] I. T. Taylor, 1973, "The Relationship between Cooling Rate and Age-Hardening Characteristics of a Number of Aluminium-Magnesium-Silicide Alloys", Canadian Journal of Metallurgy, 12, pp.93-103.
[46] C. Gallais, A. Denquin, Y. Bréchet and G. Lapasset, 2008, "Precipitation Microstructures in an AA6056 Aluminium Alloy after Friction Stir Welding: Characterization and Modelling", Materials Science and Engineering A, 496, pp.77-89.
[47] Alumatter, 2013, "Corrosion and Corrosion Control", http://aluminium.matter. org.uk/content/html/eng/default.asp?catid=177&pageid=2144416642.
[48] O. R. Myhr and O. Grong, 2011, "A Combined Precipitation, Yield Strength and Work Hardening Model for Al-Mg-Si Alloys", 11th International Summer School on Aluminium Alloy Technology, Thermo-mechanical Processing and Forming, Trondheim, Norway.
[49] H.S. Hasting, 2006, "Clustering and Precipitation in 6XXX Al Alloys: TEM and APT Studies", Department of Physics, Norwegian University of Science and Technology.
[50] O. Grong, 2012, "Recent Advances in Solid-State Joining of Aluminium", Welding journal, 91(1), pp.26–33.
[51] D. Steele, D. Evans, P. Nolan and D. J. Lloyd, 2007, "Quantification of Grain Boundary Precipitation and the Influence of Quench Rate In 6XXX Aluminium Alloys", Materials Characterization, 58, pp.40-45.
[52] R. P. Garrett, J. Lin, and T. A. Dean, 2005, "An Investigation of the Effects of Solution Heat Treatment on Mechanical Properties for AA 6XXX Alloys: Experimentation and Modelling", International Journal of Plasticity, 21 (8), pp. 1640-1657.
[53] L. P. Troeger and E. A. Starke, 2000, "Microstructural and Mechanical Characterization of a Superplastic 6XXX Aluminium Alloy", Materials Science and Engineering A, 277 (1-2), pp. 102-113
[54] King power, 'Aluminium Profile supplier Kingpower Aluminium Industry', http://www.seobility.net/en/seocheck/www.aluminium-profile-extrusion.com.
[55] C. J. Dawes, 1999, 'Friction Stir Welding', www. Alueurope.eu/ talat/lectures/4410.pdf
[56] W. M. Thomas, E. D. Nicholas, J.C. Nidham, 1991, US Patent No. 5,460,317.
[57] Terry Khaled ,2005, An Outside Looks at Friction Stir Welding, Federal Aviation Administration, Lakewood, CA, USA, https://www.faa.gov/search/?omni=MainSearch&q=an+outsider+looks+
[58] ASM Handbook, 1993, "Welding, Brazing and Soldering", Vol. 6, pp. 297-324.
© COPYRIG
HT UPM
146
[59] K. E. Knipstrom and B. Pekkari, 1997, "Friction Stir Welding Process Goes Commercial", Welding Journal, 76 (9), pp. 55-57.
[60] Terry Khaled, 2005, An Outside Looks at Friction Stir Welding, Federal Aviation Administration, Lakewood, CA, USA, https://www.faa.gov/search/?omni=MainSearch&q=an+outsider+looks+
[61] P. Vilaça and W. Thomas, 2012, "Friction Stir Welding Technology", Advanced Structure Materials, 8, pp. 85-124.
[62] Y. N. Zhang, X. Cao, S. Larose and P. Wanjara, 2012, "Review of Tools for Friction Stir Welding and Processing", Canadian Metallurgical Quarterly, 51 (3), pp. 250-261.
[63] A. Heidarzadeh, H. Khodaverdizadeh, A. Mahmoudi, and Nazari, E., (2012), “Tensile Behavior of Friction Stir Welded AA6061-T4 Aluminum Alloy Joints”, Materials and Design, 37, pp. 166–173.
[64] W. B. Lee, Y. M. Yeon, and S. B. Jung, 2004, “Mechanical Properties Related to Microstructural Variation of 6061 Al Alloy Joints by Friction Stir Welding”, Materials Transactions, 45(5), pp. 1700-1705.
[65] S. R. Ren, Z. Y. Ma, and I.Q. Chen, 2007, “Effect of Welding Parameters on Tensile Properties And Fracture Behavior of Friction Stir Welded Al–Mg–SiAlloy”, Scripta Materialia, 56, pp. 69–72.
[66] W. Tao, Z. Yong, L.Xuemei, and K. Matsuda, 2016, “Special grain boundaries in the nugget zone of friction stir welded AA6061-T6 under various welding parameters” Materials Science and Engineering: A, 671, pp.7-16.
[67] P. K. Sahu, S. Pal, S. K. Pal, and R. Jain, R., 2016, “Influence of plate position, tool offset and tool rotational speed on mechanical properties and microstructures of dissimilar Al/Cu friction stir welding joints”, Journal of Materials Processing Technology, 235, pp.55-67.
[68] L. Giraud, H. Robe, C. Claudin, C. Desrayaud, P. Bocher, and E. Feulvarch, 2016, “Investigation into the dissimilar friction stir welding of AA7020-T651 and AA6060-T6”, Journal of Materials Processing Technology, 235, pp.220-230.
[69] I. Hejazi, and S. E. Mirsalehi, 2016, “Mechanical and metallurgical characterization of AA6061 friction stir welded joints using microhardness map”, Transactions of Nonferrous Metals Society of China, 26(9), pp.2313-2319.
[70] D. Yi, T. Onuma, S. Mironov, Y. S. Sato, and H. Kokawa, 2016, “Evaluation of heat input during friction stir welding of aluminium alloys” Science and Technology of Welding and Joining, pp.1-6.
[71] N. T. Kumbhar and K. Bhanumurthy, 2008, “Friction Stir Welding of Al 6061 Alloy”, Asian Journal of Experimental Science, 22(2), pp. 63-74.
[72] S. Babu., R. M. G. Janaki, P. V. Venkitakrishnan, R. G. Madhusudhan. and K. R. Prasad, 2012, “Microstructure and Mechanical Properties of Friction Stir Lap
© COPYRIG
HT UPM
147
Welded Aluminum Alloy AA2014”, Journal of Material Science and Technology, 28(5), pp. 414-426.
[73] L. Liu, H. Nakayama, S. Fukumoto, A. Yamamoto, and H. Tsubakino, 2003, “Microscopic Observation of friction Stir Welded 6061 Aluminium Alloy”, Autumn Meeting of the Japan Institute of Metals, Sapporo, Japan P: 288-291
[74] A. Hakan, A. Bayram, and D. Ismail, 2010, “The effect of post-weld heat treatment on the mechanical properties of 2024-T4 friction stir-welded joints”, Materials and Design, 31, pp. 2568–2577.
[75] S. Chaitanya, K. D. Dheerendra, and K. Pradeep, 2013, “Effect of post weld heat treatments on microstructure and mechanical properties of friction stir welded joints of Al–Zn–Mg alloy AA7039”, Materials and Design, 43, pp. 134–143.
[76] A. E. El-Danaf and M. M. El-Rayes, 2013, “Microstructure and mechanical properties of friction stir welded 6082 AA in as welded and post weld heat treated conditions”, Materials and Design, 46, pp. 561–572.
[77] G. Ipekoglu, S. IL Erim, and C. Gurel, 2014, “Investigation into the Influence of Post-Weld Heat Treatment on the Friction Stir Welded AA6061 Al-Alloy Plates with Different Temper Conditions”, Metallurgical And Materials Transactions A, 45A, pp. 877-886.
[78] K. Elangovan and V. Balasubramanian, 2008, “Influences of post-weld heat treatment on tensile properties of friction stir-welded AA6061 aluminum alloy joints”, Material Characterization, 59, pp. 1168-1177.
[79] B. Jitlada, K. Sookkaew, U. Kanokwan, D. Jirapan, B. Chatdanai, and S. Narin, 2015, “Post-Weld Heat Treatment Effects on Hardness and Impact Strength of Aluminum Alloy 6061 Friction Stir Butt Weld”, Materials Transactions, Vol. 56, No. 7, pp. 1072 to 1076.
[80] K. Elangovan, V. Balasubramanian, and S. Babu, 2009, "Predicting tensile strength of friction stir welded AA6061 aluminium alloy joints by a mathematical model", Materials & Design, 30(1), pp. 188-193.
[81] W. J. Arbegast, 2003, "Modeling friction stir joining as a metalworking process", Proceedings of Hot Deformation of Aluminum Alloys III, pp. 313-327.
[82] W. J. Arbegast, 2005, "Using process forces as a statistical process control tool for friction stir welds", in Friction Stir Welding and Processing III as held at the 2005 TMS Annual Meeting, pp. 193-204.
[83] K. Colligan, 1999, "Material flow behavior during friction welding of aluminum", Weld J, 75(7), pp. 229s-237s.
[84] A. K. Hussain and S. A. P. Quadri, 2010, "Evaluation of parameters of friction stir welding for aluminium AA6351 alloy", International journal of engineering science and technology, 2(10), pp. 5977-5984.
[85] W. J. Arbegast, 2003, "Friction Stir Joining: Characteristic Defects", Advanced Materials Processing Center,
© COPYRIG
HT UPM
148
[86] Á. Meilinger and I. Török, 2013, "The importance of friction stir welding tool", Production Processes and Systems, 6(1), pp. 25-34.
[87] W. M. Thomas, E. D. Nicholas, J. C. Needham, P. Temple-Smith, S. W. K. W. Kallee, and J. C. Dawes, 1996, "Friction Stir Welding," UK Patent application, GB 2306366A.
[88] M. Mehta, A. Arora, A. De, and T. DebRoy, 2011, "Tool geometry for friction stir welding—optimum shoulder diameter", Metallurgical and Materials Transactions A, 42(9), pp. 2716-2722.
[89] W. Thomas and R. Andrews, 1999, "High Performance tools for friction stir welding", International Patent specification, PCT/GB99/01128, 13,
[90] P. Lacki, Z. Kucharczyk, R. Śliwa, and T. Gałaczyński, 2013, "Effect of tool shape on temperature field in friction stir spot welding", Archives of metallurgy and materials, 58(2), pp. 595-599.
[91] W. M. Thomas, D. Staines, I. Norris, and R. De Frias, 2003, "Friction stir welding tools and developments", Welding in the World, 47(11-12), pp. 10-17.
[92] M. Yuqing, K. Liming, L. Fencheng, C. Yuhua, and X. Li, 2016, “Effect of tool pin-tip profiles on material flow and mechanical properties of friction stir welding thick AA7075-T6 alloy joints” The International Journal of Advanced Manufacturing Technology, pp.1-12.
[93] Z. Chen, T. Pasang, and Y. Qi, 2008, "Shear flow and formation of Nugget zone during friction stir welding of aluminium alloy 5083-O", Materials Science and Engineering: A, 474(1), pp. 312-316.
[94] A. Leonard and S. Lockyer, 2003, "Flaws in friction stir welds", in 4th International Symposium on Friction Stir Welding.
[95] M. Kadlec, R. Růžek, and L. Nováková, 2015, "Mechanical behaviour of AA 7475 friction stir welds with the kissing bond defect", International Journal of Fatigue, 74, pp. 7-19.
[96] Y. S. Sato, H. Takauchi, S. H. C. Park, and H. Kokawa, 2005, "Characteristics of the kissing-bond in friction stir welded Al alloy 1050", Materials Science and Engineering: A, 405(1), pp. 333-338.
[97] D. Maisonnette, M. Suery, D. Nelias, P. Chaudet, and T. Epicier, 2011, "Effects of heat treatments on the microstructure and mechanical properties of a 6061 aluminium alloy", Materials Science and Engineering: A, 528(6), pp. 2718-2724.
[98] Y. Liu, W. Wang, J. Xie, S. Sun, L. Wang, Y. Qian, et al., 2012, "Microstructure and mechanical properties of aluminum 5083 weldments by gas tungsten arc and gas metal arc welding", Materials Science and Engineering: A, 549, pp. 7-13.
[99] A. Kumar and S. Sundarrajan, 2009, "Effect of welding parameters on mechanical properties and optimization of pulsed TIG welding of Al-Mg-Sialloy", The International Journal of Advanced Manufacturing Technology, 42(1-2), pp. 118-125.
© COPYRIG
HT UPM
149
[100] A. Kumar and S. Sundarrajan, 2009, "Optimization of pulsed TIG welding process parameters on mechanical properties of AA 5456 Aluminum alloy weldments", Materials & Design, 30(4), pp. 1288-1297.
[101] T. S. Kumar, V. Balasubramanian, and M. Sanavullah, 2007, "Influences of pulsed current tungsten inert gas welding parameters on the tensile properties of AA 6061 aluminium alloy", Materials & design, 28(7), pp. 2080-2092.
[102] P. J. Modenesi, E. R. Apolinario, and I. M. Pereira, 2000, "TIG welding with single-component fluxes", Journal of materials processing technology, 99(1), pp. 260-265.
[103] Z. Zhu, C. Deng, Y. Wang, Z. Yang, J. Ding, and D. Wang, 2015, "Effect of post weld heat treatment on the microstructure and corrosion behavior of AA2219 aluminum alloy joints welded by variable polarity tungsten inert gas welding", Materials & Design, 65, pp. 1075-1082.
[104] M. Ishak, N. Noordin, A. Razali, L. Shah, and F. Romlay, 2015, "Effect of filler on weld metal structure of AA6061 aluminum alloy by tungsten inert gas welding", International Journal of Automotive and Mechanical Engineering, 11, p. 2438.
[105] T. Borchers, A. Seid, S. Babu, P. Shafer, and W. Zhang, 2015, "Effect of filler metal and post-weld friction stir processing on stress corrosion cracking susceptibility of Al–Zn–Mg arc welds", Science and Technology of Welding and Joining, 20(6), pp. 460-467.
[106] M. Dewan, J. Liang, M. Wahab, and A. Okeil, 2013, "Post-weld residual stresses and heat treatments of Gas Tungsten Arc Welded aluminum alloy AA6061-T651", World Journal of Engineering, 10(1), pp. 11-22.
[107] Z. Nikseresht, F. Karimzadeh, M. Golozar, and M. Heidarbeigy, 2010, "Effect of heat treatment on microstructure and corrosion behavior of Al6061 alloy weldment", Materials & Design, 31(5), pp. 2643-2648.
[108] O. Myhr, Ø. Grong, H. Fjaer, and C. Marioara, 2004, "Modelling of the microstructure and strength evolution in Al–Mg–Si alloys during multistage thermal processing", Acta Materialia, 52(17), pp. 4997-5008.
[109] V. Balasubramanian, V. Ravisankar, and G. M. Reddy, 2008, "Influences of pulsed current welding and post weld aging treatment on fatigue crack growth behaviour of AA7075 aluminium alloy joints", International Journal of Fatigue, 30(3), pp. 405-416.
[110] N. K. Babu, M. K. Talari, D. Pan, Z. Sun, J. Wei, and K. Sivaprasad, 2012, "Microstructural characterization and grain refinement of AA6082 gas tungsten arc welds by scandium modified fillers", Materials Chemistry and Physics, 137(2), pp. 543-551.
[111] K. P. Rao, N. Ramanaiah, and N. Viswanathan, 2008, "Partially melted zone cracking in AA6061 welds", Materials & Design, 29(1), pp. 179-186.
[112] L. Shah, N. A. A. Razak, A. Juliawati, and M. Ishak, 2013, "Investigation on the Mechanical Properties of TIG Welded AA6061 Alloy Weldments Using
© COPYRIG
HT UPM
150
Different Aluminium Fillers", GSTF Journal of Engineering Technology (JET), 2(2), p. 116.
[113] M. Ericsson and R. Sandström, 2003, "Influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG", International Journal of Fatigue, 25(12), pp. 1379-1387.
[114] A. Squillace, A. De Fenzo, G. Giorleo, and F. Bellucci, 2004, "A comparison between FSW and TIG welding techniques: modifications of microstructure and pitting corrosion resistance in AA 2024-T3 butt joints", Journal of Materials Processing Technology, 152(1), pp. 97-105.
[115] A. C. Munoz, G. Rückert, B. Huneau, X. Sauvage, and S. Marya, 2008, "Comparison of TIG welded and friction stir welded Al–4.5 Mg–0.26 Sc alloy", journal of materials processing technology, 197(1), pp. 337-343.
[116] J. Zhao, F. Jiang, H. Jian, K. Wen, L. Jiang, and X. Chen, 2010, "Comparative investigation of tungsten inert gas and friction stir welding characteristics of Al–Mg–Sc alloy plates", Materials & Design, 31(1), pp. 306-311.
[117] Z.-b. He, Y.-Y. Peng, Z.-M. Yin, and X.-f. Lei, 2011, "Comparison of FSW and TIG welded joints in Al-Mg-Mn-Sc-Zr alloy plates", Transactions of Nonferrous Metals Society of China, 21(8), pp. 1685-1691.
[118] V. Fahimpour, S. Sadrnezhaad, and F. Karimzadeh, 2012, "Corrosion behavior of aluminum 6061 alloy joined by friction stir welding and gas tungsten arc welding methods", Materials & Design, 39, pp. 329-333.
[119] I. Todhunter and K. Pearson, 2014, A History of the Theory of Elasticity and of the Strength of Materials: Cambridge University Press.
[120] C. Huygens, 1967, Traite de la lumiere. Où sont expliquées les causes de ce qui luy arrive dans la reflexion, & dans la refraction. Et particulierment dans l'etrange refraction du cristal d'Islande, par CHDZ Avec un Discours de la cause de la pesanteur: chez Pierre Vander Aa marchand libraire.
[121] E. Hodgkinson, 1835, "On the collision of imperfectly elastic bodies", Rep. Br. Assoc. Adv. Sci, 4, pp. 534-543.
[122] W. C. Unwin, 1897, A new indentation test for determining the hardness of metals: Institution.
[123] T. A. Jaggar, 1897, "A microsclerometer, for determining the hardness of minerals", American Journal of Science, (24), pp. 399-412.
[124] F. C. Calvert and R. Johnson, 1859, "On the hardness of metals and alloys", Journal of the Franklin Institute, 67(3), pp. 198-203.
[125] G. Middelberg, 1886, "The hardness of metals", Engineering, 42, p. 481.
[126] W. C. Unwin, 1916, "Report of the Hardness Tests Research Committee", Proceedings of the Institution of Mechanical Engineers, 91(1), pp. 677-778.
[127] A. Outerbridge Jr and A. Allen, 1908, "Ballentine's Process of Testing the Hardness and Density of Metals",
© COPYRIG
HT UPM
151
[128] J. Brinell, 1900, "Ein Verfahren zur Härtebestimmung nebst einigen Anwendungen desselben", Gießlers Baumaterilienkunde, 5,
[129] A. Martens, 1898, Handbuch der Materialenkunde. Berlin: Springer.
[130] E. Meyer, 1908, "Untersuchungen u¨ber Ha¨rtepru¨ fung und Ha¨ rte", Phys. Z., 9, pp. 66–74.
[131] G. Berg and P. Grau, 1997, "Meyer's hardness law and its relation to other measures of ball hardness tests", Crystal Research and Technology, 32(1), pp. 149-154.
[132] M. Sakai, 1999, "The Meyer hardness: a measure for plasticity?", Journal of Materials Research, 14(09), pp. 3630-3639.
[133] J. Vincent, 1900, "Experiments on impact", in Proc. Camb. Phil. Soc, pp. 332-357.
[134] A. Shore, 1907, "An instrument for testing hardness", Am. Mach, 30, pp. 747-751.
[135] A. Shore, 1910, "On the scleroscope", in Am. Soc. Testing Materials, pp. 490-517.
[136] A. Shore and R. Hadfield, 1918, "Report on hardness testing: Relation between ball hardness and scleroscope hardness", J. Iron Steel Inst, 98, pp. 59-88.
[137] S. P. Rockwell, 1924, "Hardness testing machine," US, 1,516,207.
[138] S. N. Petrenko, 1930, "Relationships Between the Rockwell and Brinell Numbers", Bur. Stand. J. Res., 5, pp. 19-50.
[139] S. R. Williams, 1942, Hardness and hardness measurements. Cleveland, OH: The American Society for Metals.
[140] E. Berkovich, 1951, "Three-faceted diamond pyramid for micro-hardness testing", Ind. Diamond Rev, 11(127), pp. 129-133.
[141] E. Meyer, 1908, "Untersuchungen u¨ber Ha¨rtepru¨ fung und Ha¨rte", Z. Ver. Dtsch Ing., 52, pp. 645–654, 740–748, 835–844.
[142] G. F. V. Voort and G. Lucas. 1998, 23-September-2015. Microindentation Hardness Testing. Available: http://www.metallography.com/amp/micro.htm.
[143] 23-September-2015. Indentation Hardness - Microindentation Tests. Available: http://www.liquisearch.com/indentation_hardness/microindentation_tests.
[144] C. A. Schuh, 2006, "Nanoindentation studies of materials", Materials Today, 9(5), pp. 32-40.
[145] M. N. Zulkifli, A. Jalar, S. Abdullah, I. A. Rahman, and N. K. Othman, 2013, "Effect of applied load in the nanoindentation of gold ball bonds", Journal of electronic materials, 42(6), pp. 1063-1072.
© COPYRIG
HT UPM
152
[146] A. Fischer-Cripps, 2004, "A simple phenomenological approach to nanoindentation creep", Materials Science and Engineering: A, 385(1), pp. 74-82.
[147] N. Huber and J. Heerens, 2008, "On the effect of a general residual stress state on indentation and hardness testing", Acta Materialia, 56(20), pp. 6205-6213.
[148] Y.-H. Lee and D. Kwon, 2003, "Measurement of residual-stress effect by nanoindentation on elastically strained (100) W", Scripta Materialia, 49(5), pp. 459-465.
[149] S. Suresh and A. Giannakopoulos, 1998, "A new method for estimating residual stresses by instrumented sharp indentation", Acta Materialia, 46(16), pp. 5755-5767.
[150] J. Sadie and R. Sankaran, 2014, "TI 900 TriboIndenter Nanoindenter User Manual ", L. B. N. Lab.
[151] X. Li and B. Bhushan, 2002, "A review of nanoindentation continuous stiffness measurement technique and its applications", Materials characterization, 48(1), pp. 11-36.
[152] W. C. Oliver and G. M. Pharr, 1992, "An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments", Journal of materials research, 7(06), pp. 1564-1583.
[153] I. N. Sneddon, 1965, "The relation between load and penetration in the axisymmetric Boussinesq problem for a punch of arbitrary profile", International journal of engineering science, 3(1), pp. 47-57.
[154] A. C. Fischer-Cripps, 2011, Nanoindentation, Third ed. New York: springer. .
[155] M. R. VanLandingham, J. S. Villarrubia, W. F. Guthrie, and G. F. Meyers, 2001, "Nanoindentation of polymers: an overview", in Macromolecular symposia, pp. 15-44.
[156] D. Beegan, S. Chowdhury, and M. Laugier, 2005, "Work of indentation methods for determining copper film hardness", Surface and Coatings Technology, 192(1), pp. 57-63.
[157] G. Pharr, 1998, "Measurement of mechanical properties by ultra-low load indentation", Materials Science and Engineering: A, 253(1), pp. 151-159.
[158] A. Bolshakov and G. Pharr, 1998, "Influences of pileup on the measurement of mechanical properties by load and depth sensing indentation techniques", Journal of materials research, 13(04), pp. 1049-1058.
[159] J.-Y. Kim, K.-W. Lee, J.-S. Lee, and D. Kwon, 2006, "Determination of tensile properties by instrumented indentation technique: Representative stress and strain approach", Surface and Coatings Technology, 201(7), pp. 4278-4283.
[160] A. Giannakopoulos and S. Suresh, 1999, "Determination of elastoplastic properties by instrumented sharp indentation", Scripta materialia, 40(10), pp. 1191-1198.
© COPYRIG
HT UPM
153
[161] R. Ambriz, D. Chicot, N. Benseddiq, G. Mesmacque, and S. de La Torre, 2011, "Local mechanical properties of the 6061-T6 aluminium weld using micro-traction and instrumented indentation", European Journal of Mechanics-A/Solids, 30(3), pp. 307-315.
[162] E. Koumoulos, C. Charitidis, N. Daniolos, and D. Pantelis, 2011, "Nanomechanical properties of friction stir welded AA6082-T6 aluminum alloy", Materials Science and Engineering: B, 176(19), pp. 1585-1589.
[163] C. Charitidis, D. Dragatogiannis, E. Koumoulos, and I. Kartsonakis, 2012, "Residual stress and deformation mechanism of friction stir welded aluminum alloys by nanoindentation", Materials Science and Engineering: A, 540, pp. 226-234.
[164] M. Cabibbo, A. Forcellese, M. El Mehtedi, and M. Simoncini, 2014, "Double side friction stir welding of AA6082 sheets: Microstructure and nanoindentation characterization", Materials Science and Engineering: A, 590, pp. 209-217.
[165] American Welding Society, 2010, AWS D17.3/ D13.3M, “Specification for Friction Stir Welding of Aluminium Alloys for Aerospace Applications”, American national standard.
[166] Metals Handbook, 2003, Vol. 4, "Heat Treating", ASM International.
[167] “Standard Test Method for Macro etching Metals and Alloys”, 1999, ASTM Standard, E340.
[168] “Standard Test Method for Micro etching Metals and Alloys”, 2007, ASTM Standard, E407.
[169] “Standard Test Method for Knoop and Vickers Hardness of Materials”, 2011, ASTM Standard, E384.
[170] D. Chicot, M. Y. N'Jock, E. Puchi-Cabrera, A. Iost, M. Staia, G. Louis, et al., 2014, "A contact area function for Berkovich nanoindentation: Application to hardness determination of a TiHfCN thin film", Thin Solid Films, 558, pp. 259-266.
[171] M. Y. N’jock, D. Chicot, J. Ndjaka, J. Lesage, X. Decoopman, F. Roudet, et al., 2015, "A criterion to identify sinking-in and piling-up in indentation of materials", International Journal of Mechanical Sciences, 90, pp. 145-150.
[172] R. Nandan, T. DebRoy, and H. Bhadeshia, 2008, "Recent advances in friction-stir welding–process, weldment structure and properties", Progress in Materials Science, 53(6), pp. 980-1023.
[173] A. Sedmak, R. Kumar, S. Chattopadhyaya, S. Hloch, S. Tadić, A. Djurdjević, et al., 2016, "Heat Input Effect of Friction Stir Welding on Aluminum Alloy AA 6061-T6 Welded Joint", Thermal Science, 20(2), pp. 637-641.
[174] Y. Zhang, X. Cao, S. Larose, and P. Wanjara, 2012, "Review of tools for friction stir welding and processing", Canadian Metallurgical Quarterly, 51(3), pp. 250-261.
© COPYRIG
HT UPM
154
[175] C. Xu and T. G. Langdon, 2007, "The development of hardness homogeneity in aluminum and an aluminum alloy processed by ECAP", Journal of materials science, 42(5), pp. 1542-1550.
[176] K. Jata and S. Semiatin, 2000, "Continuous dynamic recrystallization during friction stir welding of high strength aluminum alloys," DTIC Document
[177] R. Doherty, D. Hughes, F. Humphreys, J. Jonas, D. J. Jensen, M. Kassner, et al., 1997, "Current issues in recrystallization: a review", Materials Science and Engineering: A, 238(2), pp. 219-274.
[178] D. Brandon, 1966, "The structure of high-angle grain boundaries", Acta metallurgica, 14(11), pp. 1479-1484.
[179] W. Read and W. Shockley, 1950, "Dislocation models of crystal grain boundaries", Physical Review, 78(3), p. 275.
[180] R. Fonda and J. Bingert, 2007, "Texture variations in an aluminum friction stir weld", Scripta Materialia, 57(11), pp. 1052-1055.
[181] S. Mironov, K. Inagaki, Y. S. Sato, and H. Kokawa, 2015, "Effect of welding temperature on microstructure of friction-stir welded aluminum alloy 1050", Metallurgical and Materials Transactions A, 46(2), pp. 783-790.
[182] V. Niranjani, K. H. Kumar, and V. S. Sarma, 2009, "Development of high strength Al–Mg–Si AA6061 alloy through cold rolling and ageing", Materials Science and Engineering: A, 515(1), pp. 169-174.
[183] M. Ferry and F. Humphreys, 1996, "Discontinuous subgrain growth in deformed and annealed {110}< 001> aluminium single crystals", Acta materialia, 44(4), pp. 1293-1308.
[184] A. Gupta, D. Lloyd, and S. Court, 2001, "Precipitation hardening processes in an Al–0.4% Mg–1.3% Si–0.25% Fe aluminum alloy", Materials Science and Engineering: A, 301(2), pp. 140-146.
[185] A. A. Zadpoor, J. Sinke, and R. Benedictus, 2009, "Fracture mechanism of aluminium friction stir welded blanks", International Journal of Material Forming, 2(1), pp. 319-322.
[186] Hormbogen E, Koster U, in: F. Haessner, Dr. Riederer (Eds.),1978, "Recrystallization of metallic materials", Verlag, Berlin, p.159.
[187] D. Lucca, K. Herrmann, and M. Klopfstein, 2010, "Nanoindentation: Measuring methods and applications", CIRP Annals-Manufacturing Technology, 59(2), pp. 803-819.
[188] J. Loubet, M. Bauer, A. Tonck, S. Bec, and B. Gauthier-Manuel, 1993, "Nanoindentation with a surface force apparatus," in Mechanical Properties and Deformation Behavior of Materials Having Ultra-Fine Microstructures, ed: Springer, pp. 429-447.
[189] D. Chicot, M. Y. N'Jock, E. Puchi-Cabrera, A. Iost, M. Staia, G. Louis, et al., 2014, "A contact area function for Berkovich nanoindentation: Application to
© COPYRIG
HT UPM
155
hardness determination of a TiHfCN thin film", Thin Solid Films, 558, pp. 259-266.
[190] D. Chicot, 2009, "Hardness length-scale factor to model nano-and micro-indentation size effects", Materials Science and Engineering: A, 499(1), pp. 454-461.
[191] L. Charleux, V. Keryvin, M. Nivard, J.-P. Guin, J.-C. Sanglebœuf, and Y. Yokoyama, 2014, "A method for measuring the contact area in instrumented indentation testing by tip scanning probe microscopy imaging", Acta Materialia, 70, pp. 249-258.
[192] J. Gong, H. Miao, and Z. Peng, 2004, "On the contact area for nanoindentation tests with Berkovich indenter: case study on soda-lime glass", Materials letters, 58(7), pp. 1349-1353.
[193] M. Abdel-Karim, 2011, "Effect of elastic modulus variation during plastic deformation on uniaxial and multiaxial ratchetting simulations", European Journal of Mechanics-A/Solids, 30(1), pp. 11-21.
[194] T. Ganaha, B. Pearce, and H. Kerr, 1980, "Grain structures in aluminum alloy GTA welds", Metallurgical Transactions A, 11(8), pp. 1351-1359.
[195] S. Kou and Y. Le, 1988, "Welding parameters and the grain structure of weld metal—A thermodynamic consideration", Metallurgical Transactions A, 19(4), pp. 1075-1082.
[196] S. Yan, H. Chen, Z. Zhu, and G. Gou, 2014, "Hybrid laser-metal inert gas welding of Al–Mg–Si alloy joints: microstructure and mechanical properties", Materials & Design, 61, pp. 160-167.
[197] A. Hadadzadeh, M. M. Ghaznavi, and A. H. Kokabi, 2014, "The effect of gas tungsten arc welding and pulsed-gas tungsten arc welding processes’ parameters on the heat affected zone-softening behavior of strain-hardened Al–6.7 Mg alloy", Materials & Design, 55, pp. 335-342.
[198] Y. Zhang, C. Pan, and A. Male, 2000, "Improved microstructure and properties of 6061 aluminum alloy weldments using a double-sided arc welding process", Metallurgical and Materials Transactions A, 31(10), pp. 2537-2543.
[199] G. Saad, S. Fayek, A. Fawzy, H. Soliman, and E. Nassr, 2014, "Work hardening characteristics of gamma-ray irradiated Al-5356 alloy", Materials Science and Engineering: A, 607, pp. 132-137.
[200] G. Saad, S. Fayek, A. Fawzy, H. Soliman, and E. Nassr, 2010, "Serrated flow and work hardening characteristics of Al-5356 alloy", Journal of Alloys and Compounds, 502(1), pp. 139-146.
[201] V. Balasubramanian, V. Ravisankar, and G. M. Reddy, 2008, "Effect of pulsed current welding on fatigue behaviour of high strength aluminium alloy joints", Materials & Design, 29(2), pp. 492-500.
[202] C. Liu, R. Jing, Q. Wang, B. Zhang, Y. Jia, M. Ma, et al., 2012, "Fabrication of Al/Al 3 Mg 2 composite by vacuum annealing and accumulative roll-bonding process", Materials Science and Engineering: A, 558, pp. 510-516.
© COPYRIG
HT UPM
156
[203] D.-H. Choi, B.-W. Ahn, D. J. Quesnel, and S.-B. Jung, 2013, "Behavior of β phase (Al 3 Mg 2) in AA 5083 during friction stir welding", Intermetallics, 35, pp. 120-127.
[204] S. Scudino, S. Sperling, M. Sakaliyska, C. Thomas, M. Feuerbacher, K. Kim, et al., 2008, "Phase transformations in mechanically milled and annealed single-phase β-Al 3 Mg 2", Acta materialia, 56(5), pp. 1136-1143.
[205] I. Golovin, A. Mikhaylovskaya, and H.-R. Sinning, 2013, "Role of the β-phase in grain boundary and dislocation anelasticity in binary Al–Mg alloys", Journal of Alloys and Compounds, 577, pp. 622-632.
[206] O. Kogtenkova, S. Protasova, A. Mazilkin, B. Straumal, P. Zięba, T. Czeppe, et al., 2012, "Heat effect of grain boundary wetting in Al–Mg alloys", Journal of Materials Science, 47(24), pp. 8367-8371.
[207] C. Luo, W. Liang, Z. Chen, J. Zhang, C. Chi, and F. Yang, 2013, "Effect of high temperature annealing and subsequent hot rolling on microstructural evolution at the bond-interface of Al/Mg/Al alloy laminated composites", Materials Characterization, 84, pp. 34-40.
[208] G. Scamans and A. Rehal, 1979, "Electron metallography of the aluminium-water vapour reaction and its relevance to stress-corrosion susceptibility", Journal of Materials Science, 14(10), pp. 2459-2470.
[209] G. Scamans, N. Holroyd, and C. Tuck, 1987, "The role of magnesium segregation in the intergranular stress corrosion cracking of aluminium alloys", Corrosion science, 27(4), pp. 329-347.
[210] L. Liu, H. Nakayama, S. Fukumoto, A. Yamamoto, and H. Tsubakino, 2004, "Microscopic observations of friction stir welded 6061 aluminum alloy", Materials Transactions, 45(2), pp. 288-291.
[211] U. Suhuddin, S. Mironov, Y. Sato, and H. Kokawa, 2010, "Grain structure and texture evolution during friction stir welding of thin 6016 aluminum alloy sheets", Materials Science and Engineering: A, 527(7), pp. 1962-1969.
[212] V. Fahimpour, S. Sadrnezhaad, and F. Karimzadeh, 2013, "Microstructure and Mechanical Property Change During FSW and GTAW of Al6061 Alloy", Metallurgical and Materials Transactions A, 44(5), pp. 2187-2195.
[213] J.-k. Ding, D.-p. Wang, W. Ying, and D. Hui, 2014, "Effect of post weld heat treatment on properties of variable polarity TIG welded AA2219 aluminium alloy joints", Transactions of Nonferrous Metals Society of China, 24(5), pp. 1307-1316.
[214] D. Lucca, K. Herrmann, and M. Klopfstein, 2010, "Nanoindentation: Measuring methods and applications", CIRP Annals-Manufacturing Technology, 59(2), pp. 803-819.
[215] M. James, D. J. Hughes, D. Hattingh, G. Mills, and P. Webster, 2009, "Residual stress and strain in MIG butt welds in 5083-H321 aluminium: As-welded and fatigue cycled", International Journal of Fatigue, 31(1), pp. 28-40.
© COPYRIG
HT UPM
157
[216] D. Chicot, F. Roudet, A. Zaoui, G. Louis, and V. Lepingle, 2010, "Influence of visco-elasto-plastic properties of magnetite on the elastic modulus: multicyclic indentation and theoretical studies", Materials chemistry and physics, 119(1), pp. 75-81.
