Study Microstructure And Mechanical Properties Of Rapidly … · 2015-08-24 · Study...

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:15 No:04 53

S I J E N IJENS © August 2015 IJENS-IJMME-2828-044415

Study Microstructure And Mechanical Properties Of

Rapidly Solidified Of Al-Sn By Melt Spinning

Technique Dr. Eman J. Abed

Dept. of Materials Engineering

University of Kufa/ Najaf/Iraq

Abstract-- The melt spinning technique has been used in this

study to produce rapidly solidified alloys in the simple binary Al-

Sn alloys.Aluminum-5,15 and 25%Sn were prepared by as cast

and melt spun technique. Optical microcopy,X-rays diffraction

analysis and scanning electron with energy dispersive

spectroscopy (EDS) were used to provide information about the

difference in microstructure and phases of as cast and rapid

solidified samples. In addition to hardness values of the ribbons

and as cast ingots also measured. The results revealed that

microstructure of the as cast alloys is formed from Sn particle

spread in a continuous Al-rich matrix, moreover thin

predendritic fine chill crystal zone at the wheel side with only Sn-

rich phase particles, which develops into a region of disordered

dendritic columnar grains. There is no solubility of Al in Sn or

vice versa in thermal equilibrium diagram of aluminum-tin alloy

system at room temperature; also, there is no intermediate phase

formed between Al and Sn by conventional production processes.

X-ray diffraction has ascertained the presence of the equilibrium

phases for rapid solidified alloys. The hardness values of melt-

spun alloys increase approximately twice higher than those of

original ingot alloy. Index Term-- rapid solidification, ribbons, microstructure,

microhardness, mechanical properties.

1. INTRODUCTION

White metals (Babbitt) and AL-Sn alloys have a

very long history to be used as plain bearing materials. These

alloys can provide excellent combination of strength and

surface properties [1]

.Al-Sn is an immiscible binary alloy

system with a solid solubility of Sn in Al below 0.09 wt.% at

room temperature. Due to the low solubility of Al-Sn alloy

and high density difference between Al (2.7g/cm3) and

Sn(7.2g/cm3),there is very strong sedimentary tendency in the

casting of Al-Sn alloy. However, it is very difficult obtain

homogeneous distribution of Sn in Al matrix. There is

different preparing techniques, including rapid solidification,

physical vapor deposition, electro deposition, powder

metallurgy, severe plastic deformation, and mechanical

alloying, have been used to improve homogeneity and refine

the size of Sn phase in Al-Sn alloys [2]

.

The industrial use of metallic materials is limited by their

physical, mechanical properties, microstructure and,

characteristics that are greatly influenced by the initial casting

conditions. During slow cooling in large industrial ingots a

considerable amount of segregation takes place due to the

different solubilities in the solid and the liquid, and this cannot

be improved via a solid-state thermal treatment. A rapid

solidification can successfully overcome the problems

connected with segregation and produce fine-grained,

segregation-free materials with an unusual chemical

composition and unique mechanical properties [3]

.

Rapidly solidified materials differ a great deal from

materials with the same chemical composition prepared by

conventional casting procedures in terms of the refinement of

the main structural constituents .As a result of non-equilibrium

freezing, they may also contain supersaturated phases,

metastable intermediate phases or, in limited cases,amorphous

constituents[3]

. Rapid solidification is defined in the scientific

literature as the rapid extraction of thermal energy to include

both superheat and latent heat during the transition from a

liquid state at high temperatures, to solid material at room.

The rapid extraction of heat can cause under cooling as high

as 100 Cᵒ or more prior to the initiation of solidification. The

time at high temperatures is limited to milli-seconds followed

by rapid quenching to room temperature. The choice of the

quenching medium, may be it water, brine solution, or liquid

nitrogen, has a profound influence on solidification time and

the resultant microstructural development to include the

distribution of phases in the final part. The high-cooling rate

results in a significant amount of undercooling of the melt,

which is conducive for the occurrence of several metastable

effects that can be categorized as being either constitutional or

Microstructural [4]

.

The quick extraction of thermal energy that occurs during

rapid solidification permits large deviations from equilibrium,

which provides the advantages of the intrinsic microstructural

effects include either one or a combination of changes in grain

morphology, refinement of characteristics, such as, the size

and shape of grains, and the shape and location of the phases

present [4,5]

.

In the present work, three compositions of aluminium

base alloy (Al-,5%,15% and 25%Sn) alloys were prepared by

using the melt-spinning technique to study the structure, and

also to the effect of hardness of the melt spun ribbons

produced.

2. EXPERIMENTAL

Experimental procedure gives a detailed description

of material and experimental methods as well as apparatuses

used in this research. Also give describe effects the

composition of tin on solidification rate of Al-Sn alloys and on



microstructures of as cast and melt-spun ribbons. Analysis of

the data is carried out using different techniques such as

scanning electron scanning electron microscopy (INSPECT-

550) operated at 5 kV and linked with an Energy Dispersive

Spectrometry (EDS) attachment. Although the wide use of Al-

Sn alloys for engineering applications studies on the

Microstructural development of such materials are rare.

Optimized microstructures during the solidification stage of

processing can be used for final properties. Three

compositions of aluminium base alloy (Al-,5%,15% and

25%Sn) alloys were prepared by using the melt-spinning

technique to study the structure, and also to the effect of

hardness of the melt spun ribbons produced.

2.1 MATERIALS High purity aluminium (99.9 wt% A1) and high purity tin

with composition 99.999 wt% Sn are used in prepared of the

samples.

2.2 TOOLS AND APPARATUSES

- Melt spinning device

- Graphite crucible

- Electric arc furnace

- Infrared radiation pyrometer

- Hot mounting apparatus

- Grinding and polishing device

- Optical microscope

- Scanning electron scanning electron microscopy

(INSPECT-550) operated at 5 kV and linked with an

Energy Dispersive Spectrometry.

-X-ray diffraction device

- The Vickers microhardness tester (Digital micro

hardness USA-TH715).

2.3.1 MELT SPINNING APPARATUS

The main parts of melt spinning apparatus are a disc

made of copper based alloy with high thermal conductivity.

Alloys of copper are rather better than pure copper as their

wear resistance is superior therefore brass alloy was used in

manufacture of rotating disc which was driven by electric

motor. In the present work the 250 mm diameter brass wheel

was driven by a 1hp motor at speed 2800 rpm given

circumference velocity approximately 36 m.sec-1

.The surface

of the wheel had 200 mm wide flat used for melt spinning. To

give a mirror surface finish of rotating disc emery paper was

used and polished after every run of the wheel.

2.3.2 CRUCIBLE

The crucible performs two functions. The first is to

contain the solid and liquid materials before ejection without

either itself melting or reaction with the molten metal and the

second is to direct molten metal at the angle, height and flow

rate required to produce uniform sound ribbon. Graphite

crucible was used in this project with nozzle 2.5 mm. Graphite

was used substitute its benefits being that it was cheap and

easy to machine and so almost any profile nozzle could be

made but wear was a major problem, after a few runs the

orifice was considerably enlarged.

2.3.3 EXPERIMENTAL PROCEDURE 2.3.3.1 AS CAST ALLOYS PREPARATION

Aluminium-tin alloys with compositions 5,15 and 25 %

Sn were prepared from 99.9 wt% A1 and 99.999 wt% Sn.

Electric resistance furnace model (SX 5-12) was used for

melting the metals to preparation of the specimens at 750 C°

in graphite crucible and the required amount of tin was added

to the molten aluminum then mixing the molten metal for a

few minute, and holding at this temperature for a sufficient

length of time for homogenous and then poured into steel die

with internal diameter 15 mm.

Rapidly solidified alloys were produced by free jet melt

spinning in air by means of impinging a jet of molten alloys

with nozzle diameter 2.5 mm onto the cylindrical surface of a

polished brass wheel (250 mm diameter, 200 m wide flat) and

rotating at 2800 rpm. To clean the rotating disc grinding paper

was after each pass. The measuring of temperature crucible

before ejection was performed using infrared radiation

pyrometer 450 C°. As the wheel moves, the metal solidifies

and separation in the form of a very fine ribbons.

The measuring of temperature for molten metal and

crucible were performed using infrared radiation pyrometer.

The temperature of empty crucible before ejection = 450 C°.

The temperature of molten metal before =700 C°.

The temperature of the as-produced ribbons 100 C°.

In preparing as cast specimen for microscopically

examination it is first necessary to produce in it a surface

which appears perfectly flat and scratch free when viewed

with the aid of a microscope. This involves first grinding the

surface flat, and then polishing it to remove the marks left by

grinding stage. Grinding stage is then carried out on emery

papers of progressively finer grade. These must be of the very

best quality. Aluminum and its alloys are soft and easily

scratched or distorted during preparation. For cutting

specimens, sharp Grinding: specimens may be ground on

emery papers by grinding and polishing machine (rotary discs

of grinding paper are used). Silicon carbide papers (230, 320,

400, 600, 800, 1200, 2000 and 2500 grit) which used well

washed with water are preferred to avoid the embedding of

abrasive particles in the metal.

Polishing is carried out diamond (9 µm, 3 µm and 1 µm )

using a slowly rotating wheel. These compounds are graded

and colour-coded according to particle size (in micrometers).

Since these compounds are expensive, it is desirable that the

operator should have some manipulative skill in order that

frequent changing of the polishing pad is not made necessary

due either to tearing of the cloth or lack of cleanliness in

working. For polishing as cast samples (aluminum-tin alloys)

it is generally convenient to use a three-stage technique

necessitating two polishing wheels. Preliminary polishing is

carried out using a 9 µm particle size. The specimen is then

washed on the second wheel using a 3 µm particle size and

finished on the three stages using 1 µm particle size, then

washed and dry. Finally stage etching the samples, before

being etched the specimen must be absolutely clean; otherwise

it will undoubtedly stain during etching. The samples should



first be washed free of any adhering polishing compound. The

Al-Sn alloys were immersion in dilute hydrofluoric acid for

ten seconds. After being etched the specimen is washed in

running water and drying.

Optical microcopy was used to provide information about

the microstructure of alloy samples for as cast and rapid

solidified alloys with different magnification (50 x) by using

digital microscope DCMS10 (USB2). The microstructure of

ribbons and conventionally cast alloys were characterized

using scanning electron microscopy (SEM) together with the

energy dispersive spectroscopy (EDS)as shown in Figure 1.

SEM (INSPECT-550) was normally performed at 5 kV to

measure the surface morphology of the samples. In most

cases, the highest magnification achievable by this microscope

is 300,000X. The SEM system utilized for this work can

perform other characterization work like energy dispersive

(EDX) analysis. Specimen for X-ray diffraction analysis using

CuKα radiation (λ=1.5405Aᵒ) and scanning speed 5m/min of

2θ (Bragg angle) with range (30-80) and 40KV/30mA applied

power were composed of a number of ribbons parallel to each

other with wheel side surface. Line profiles (peaks) from the

Al-rich and Sn phases were recorded.

The hardness of the ribbons and as cast ingots measured

with a Vickers diamond indenter in a microhardness tester

(Digital micro hardness USA-TH715). In this test the applied

load is 2.9 N and then the diagonal length of the square

impression was measured by means of a microscope which

has a variable slit built into the eyepiece.

Fig. 1. Scanning Electron Microscopy (SEM) Together with the

Energy Dispersive Spectroscopy (EDS).

3. RESULTS AND DISCUSSION

3.1 MICROSTRUCTURAL INVESTIGATIONS

Microstructural investigations which include study

microstructure of slowly and rapidly solidified of Al-Sn alloys

by using optical microscope and scanning electron scanning

electron microscopy linked with an energy dispersive

spectrometry attachment.

Figure 2 shows the optical micrograph of the AL-5%Sn

Alloy that was solidified at slow cooling rate. The structure is

formed from Sn particle spread over a continuous Al-rich

matrix. Figure 3 and Figure 4 shows tin is distributed in

aluminium matrix as a separate phase in form of network

structure along the of grain boundary of aluminium and with

increase tin content results in continuous increasing of

bonding between Al matrix and Sn phase.These results are

consistent with the previous observations by A.R.Valizadeh

and his co-workers[6]

.

Fig. 2. Optical Micrographs of the Slowly Solidified of AL-5%Sn Alloy Shows Shape of Tin in Solid Solution Matrix (Magnification 50X).

AL Matrix

Sn

http://www.scielo.br/img/revistas/mr/2012nahead/html/aop_1121-11f01.htm



Fig. 3. Optical Micrographs of the Slowly Solidified of AL-15%Sn Alloy Shows Shape

of Tin in Solid Solution Matrix (Magnification 50X).

Fig. 4. Optical Micrographs of the Slowly Solidified of AL-25%Sn Alloy Shows Shape

of Tin in Solid Solution Matrix, (Magnification 50X).

Microstructural investigations in scanning electron linked

with an energy dispersive spectrometry attachment showed

that the structure of melt spun ribbons was completely

different from their conventionally cast counterparts. The

microstructure of a melt-spun ribbon of the Al-5%Sn alloy is

shown in Figure 5. It is obviously seen that the microstructure

consists of two phases a coarse α-Al dendrites together with

fine grains separate in region of primary Sn. These phases

were also confirmed by XRD analysis that consisted of two

peaks sets as indicated in Figure 6.These results are consistent

with the previous observations by many researchers [7, 8 and 9]

Figure 7 and Figure 9 shows scanning electron microscope

of the cross-section of a melt-spun ribbons of the Al-15%Sn

alloy and Al-25%Sn alloy respectively a thin predendritic fine

(chill) crystal zone at the wheel side with only Sn-rich phase

particles, which develops into a region of disordered dendritic

columnar grains with tin rich phase particles at the grain

boundaries. Energy Dispersive Spectrometry (EDS)

microanalysis in the scanning electron microscope was used to

identify the chemical composition of two phases present in

these alloys as shown in Figures 8 and 10.

a

Sn

AL Matrix

Sn



Fig. 5. SEM Images of the Rapid Solidified Ribbon of Al-5%Sn Alloys at Different Magnification.

The Bright Phase is Sn and the Dark Matrix is Al.

Fig. 6. EDS Point Wise Analysis of the Investigated Rapid Solidified AL-5% Sn Alloy,

Marker in Figure 5.

Sn

Sn

Sn



Fig. 7. SEM images of the rapid Solidified Ribbon of Al-15%Sn Alloys

at Different Magnification. The bright phase is Sn and the Dark Matrix is Al.

Fig. 8. EDS Point Wise Analysis of the Investigated

Rapid Solidified AL-15% Sn Alloy, Marker in Figure 7.

Sn

Sn



Fig. 9. SEM images of the rapid Solidified Ribbon of Al-25%Sn Alloys at Different Magnification. The bright phase is Sn and the Dark Matrix is Al.

Fig. 10. EDS Point Wise Analysis of the Investigated Rapid

Solidified AL-25% Sn Alloy, Marker in Figure 9.

Figures 11,12 and 13 shows the x-ray diffraction patterns for as- quenched melt- spun Al-Sn alloys. It is found that the

structure of all alloys consists of Aluminum matrix with Sn phase. The Sn phase precipitates in all alloys as indicated by Sn peaks

as shown in following figures. Both the number and the intensity of Sn peaks increases with increasing Sn concentration, which

indicates more precipitation of Sn phase in the Aluminum matrix and formation solid solution AL+Sn. The x-ray diffraction

patterns has ascertained the existence of the equilibrium crystalline phases fcc- Al and Sn phase in all the alloys in melt spun

condition in form sharp lines. So that rapid solidification has induced neither amorphous nor formation of metastable phases in

these alloys.

Sn



Fig. 11. The XRD Patterns of as-Quenched Melt-Spun Al-5%Sn alloys.

Fig. 12. The XRD Patterns of as-Quenched Melt-Spun Al-15%Sn alloys.

Fig. 13. The XRD Patterns of as-Quenched Melt-Spun Al-25% Sn alloys.



3.2 MICROHARDNESS INVESTIGATIONS In the present work, the microhardness of

conventionally cast ingot and rapidly solidified ribbons were

measured by Vickers microhardness measurements. The

applied load to determine the hardness was 2.942N. On the

longitudinal section of each sample, five measurements were

performed on the longitudinal section of each sample. Figure

14 shows high decreasing in the hardness values of the as cast

alloys with increasing Sn content; while increases the values

of hardness melt-spun ribbon approximately twice higher than

those of original ingot alloy. The grain size of rapidly

solidified ribbons is much smaller in compared with the grain

size of those as cast alloys due to high cooling rate. Therefore,

increase in hardness values for melt spun alloys compared

with their as cast can be attributed to grain refinement and

changes in microstructure occurred during the melt spinning

process.The comparison of Vickers microhardness values of

ribbons and ingot hardness of the three alloys in the as-cast

ingot and rapid solidified alloys is presented in Figure 14.

4. CONCLUSIONS

1. The microstructure of the AL-%Sn Alloy that was solidified

at slow cooling rate is formed from Sn particle spread over

a continuous Al-rich matrix.

2. Increase tin content results in continuous increasing of

bonding between Al matrix and Sn phase.

3. Thin predendritic fine chill crystal zone at the wheel side

with only Sn-rich phase particles, which develops into a

region of disordered dendritic columnar grains.

4. Rapid solidification enables higher amount of solute to be

retained in solid solution of alloy and also refine

microstructures thereby increasing the mechanical

properties of these alloys.

5. Scanning electron scanning electron microscopy linked with

an energy dispersive spectrometry attachment identify the

chemical composition of two phases present in these alloys.

6. Increasing hardness values of melt-spun alloys compared

with their as cast alloys.

7. The grain size of rapidly solidified ribbons is much smaller

in compared with the grain size of those as cast alloys due

to high cooling rate.

8. The x-ray diffraction patterns has as certained the existence

of the equilibrium crystalline phases.

ACKNOWLEDGMENTS The author would like to express their appreciation to the

University of Kufa/College of Engineering /Materials

Engineering Department for its support of this work. The

authors would like to thank all the technicians in the

laboratories for their valuable help.

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Al–Sn and Equivalent Al–Pb alloys under Lubrication", Bull. Mater. Sci., Vol. 26, No. 3, April 2003.

[2] X. Liu, M.Q. Zeng, Y. Ma, M. Zhu, "Wear Behavior of Al–Sn

Alloys with Different Distribution of Sn Dispersoids Manipulated by Mechanical Alloying and Sintering, ", Wear 265 (2008) 1857–

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[3] Peter Jurci, Maria Domankova, Maria Hudakova and Borivoj Sustarsic, " Microstructural Evaluation of Rapidly Solidified Al–

7Cr Melt Spun Ribbons", Materiali in tehnologije , Materials and

technology 41 (2007) 6, 283–287. [4] Enrique J. Lavernia , T. S. Srivatsan, "The Rapid Solidification

Processing of Materials: Science,Principles,Technology,

Fig. 14. Vickers Microhardness for As Cast and Melt -Spun

Ribbons Alloys.

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