INVESTIGATION OF MICROSTRUCTURE FEATURES OF AlMg9 ALLOY

Zdenka Zovko Brodarac, Jožef Medved2, Primož Mrvar2 1 University of Zagreb Faculty of Metallurgy, Aleja narodnih heroja 3, Sisak, Croatia 2 University of Ljubljana Faculty of Natural Sciences and Engineering, Aškerčeva cesta 12, Ljubljana, Slovenia

OUTLINE

INTRODUCTION - AIM OF INVESTIGATION:

Importance and application of Al-Mg alloys

Al-Mg(-Si) system

EXPERIMENTAL:

Materials and methodology

RESULTS AND DISCUSSION:

Thermodynamic analysis

Metallographic analysis

Microstructure features analysis

Correlation of microstructure features to cooling rate

CONCLUSION

INTRODUCTION

WHY Al-Mg ALLOYS? low density high strength and hardness achieved by natural aging significant corrosion resistance in see water and atmosphere dimensional stability excellent weldability suitability for recycling

APPLICATION! tool plates

complex thin-walled shapes - rotor limbs

cooling plates used by mechanical

processing

instruments housing

ship parts

gun frames

optical systems

architecture and decorative purposes

INTRODUCTION

Aluminum corner of the Al – Mg phase diagram

Solid phase distribution in aluminum reach

corner of the Al – Mg – Si diagram.

Reaction T / °C

Compositions of liquid

Mg / mass. % Si /mass.%

L→ αAl + Mg2Si (quasibinary section) 595 8,15 7,75

L→ αAl + (Si) + Mg2Si 555 4,96 12,95

L→ αAl + Mg2Si + Al8Mg5 449 32,2 0,37

Invariant reactions in ternary alloys of the Al-Mg-Si system

Al-Mg SYSTEM Al-Mg-Si SYSTEM

Characterization of microstructure features of AlMg9 alloy in different cooling condition based on:

influence of different cooling rate on the significant temperature of phase transformations during solidification and grain size of the AlMg9

alloy

phase analysis, surface area, elongation and number of grains per surface area (NA) of the corresponding microstructure related to the

cooling rates.

INTRODUCTION

THE AIM OF THIS INVESTIGATION:

EXPERIMENTAL

CASTING OF THE TEST SAMPLES -melting in the graphite pot into the induction furnace till approximately 730 °C -melt casting into the measuring cells to achieve different cooling rates in the sample:

cronning cell (standard Quick Cup equipped by the thermoelement Ni-CrNi) grey iron permanent mould of the conic shape.

CHEMICAL ANALYSIS: charge material - ingots of the quality EN 51200 (AlMg9) alloy chemical composition - spectrometer Spectro DIN 31051

THERMODYNAMICAL MODELING OF THE PHASE DIAGRAM OF THE AlMg9 ALLOY BY THE SOFTWARE Thermo-Calc (TCW 5.0) phase equilibrium - software ThermoCalc (TCW 5.0) - enable calculation of the thermodynamical stability of particular phases related to the chosen initial conditions: temperature, pressure and chemical compositions, on the foundation of the data basis.

EXPERIMENTAL

METALOGRAPHIC ANALYSIS -samples: taken in instant neighboring of the thermoelement positions, prepared by standard methods of grinding and polishing:

microstructural examination - etched in diluted HF grain size determination - electrolytic etching: U=23V, t=40s, Barker reagent

-optical microscope Olympus BX61, equipped by the automatic image analysis (Analysis®MaterialsResearchLab) -scanning electron microscope JEOL 5610 + EDS

SIMPLE AND SIMULTANEOUS THERMAL ANALYSIS -data acquisition:

Simple TA - measuring card DAQ Pad-MI0-16XE-50 and analysis by software LabView 7.0; cooling curves - drawn and processed by software Origin 7.0 Simultaneous TA - DSC by the instrument Netzsch STA 449C Jupiter; sample heating till 720 °C, heating/cooling rate 10 K/min

Marks:

- MIA – Multiple Image

Analysis; (100x)

- R – outer edge of the

sample;

- S – middle of the sample,

position where

thermoelement was placed;

Magnification:

1 – 50x; 2 – 100x; 3 – 200x;

4 – 500x; 5 – 1000x

- X – series of the

microphotographs recording;

(100x)

SAMPLE FROM THE CRONNING CELL

SAMPLE FROM THE CONIC MOULD

EXPERIMENTAL

CHEMICAL ANALYSIS

Compared chemical composition of the examined multicomponent technical alloy AlMg9 with those prescribed by norm EN 1706:2010 .

Alloy Element Si Fe Cu Mn Mg Cr Ni Zn Ti

Investigated AlMg9 w

mass.%

1,212 0,757 0,0543 0,2966 10,08 0,0034 0,0086 0,0231 0,0904

EN AC-AlMg9 2,5 1,0 0,10 0,55 8,0 -10,5

0,25 0,20

RESULTS AND DISCCUSSION

THERMODYNAMICAL MODELING OF THE PHASE DIAGRAM OF AN AlMg9 ALLOY BY THE ThermoCalc (TCW 5.0) SOFTWARE

PHASES EVALUATION:

Al13Fe4

Al6Mn

αAl

Mg2Si

AlMg-β

ZnMgMnFeCuSiTL %25,2%5%90,1%29,2%5%54,325,658 = 597,3 °C

ZnMgMnFeCuSiT SiMgE %76,10%23,2%96,7%57,0%3%17,14009,4102, = 559,5 °C

-initial condition: T = 743 °C, p = 105 MPa, default chemical composition

Thermodynamical calculation of the equilibrium phase diagram of examined AlMg9 alloy. Polytherm section of the

equilibrium phase diagram.

RESULTS AND DISCCUSSION

RESULTS AND DISCCUSSION

Dependence of the significant temperature of phase transformations from the cooling rate of the AlMg9 alloy.

RESULTS OF SIMPLE AND SIMULTANEOUS THERMAL ANALYSES

QUALITY ANALYSIS OF MICROSTRUCTURAL CONSTITUENTS OF AlMg9 ALLOY

A B

C D

Microstructure of the sample cast in croning cell, obtained on the scanning electron microscope (SEM) with the marked

places of quantitative analysis performing by EDS, magnification 200X.

αAl (matrix) - D Alx(Fe,Mn)ySiz (white phase) - B Mg2Si (black phase) - C Al8Mg5 (light grey phase) - A

RESULTS AND DISCCUSSION

METALLOGRAPHIC ANALYSIS OF AlMg9 ALLOY

3 K/s 7 K/s 55 K/s 150 K/s

Micrographs (METALOGRAPHIC ANALYSIS row) and electrolytic etched micrographs (METALOGRAPHIC ANALYSIS-GRAIN SIZE row) for the grain size determination sequence, magnification 200X, all in relation to cooling rate.

RESULTS AND DISCCUSSION

Grain size per surface area dependence from the cooling rate.

NA = -3.32 e(-rc / 4.53) – 3.60 e(-rc / 81.25) + 11.47 No.gr./mm2 R2=1

RESULTS AND DISCCUSSION

PHASE ANALYSIS OF AlMg9 ALLOY

Micrographs (SEM row) and by software analyzed corresponding micrographs (PHASE ANALYSIS row), magnification 200X, all in relation to cooling rate.

3 K/s 7 K/s 55 K/s 150 K/s

RESULTS AND DISCCUSSION

MICROSTRUCTURE DEVELOPMENT OF THE AlMg9 ALLOY

Sample phase ratio

0,00

2,00

4,00

6,00

8,00

10,00

12,00

3 7 55 150r c / K/s

f (X

, A

lMg

9)

/ a

rea

%

Alx(Fe,Mn)ySiz

Mg2Si

Al8Mg5

Surface area of particular phases

0,00

20,00

40,00

60,00

80,00

100,00

120,00

140,00

160,00

3 7 55 150r c / K/s

P

/ m

m2

Alx(Fe,Mn)ySiz

Mg2Si

Al8Mg5

Lenght of particular phases

0,00

1,00

2,00

3,00

4,00

5,00

6,00

3 7 55 150r c / K/s

l / m

m

Alx(Fe,Mn)ySiz

Mg2Si

Al8Mg5

RESULTS AND DISCCUSSION

Thermal and microstructure analysis enables calculation of mathematical models which reveals that increase of cooling rate induce:

Lowering of significant temperatures of phase transformations TL, TE1 and TS

Narrowing of solidification interval

Significant growth of NA (6 →11)

Fine and homogeneous distribution of microstructural constituents

Increase of Mg2Si phase ratio; Alx(Mn,Fe)ySiz and Al8Mg5 ratio stayed unchanged

Decrease of particles length to final ~2 μm.

On the base of particular established phases ratios, surface area and elongation dependence regard cooling rate it is possible to predict microstructure development

of the multicomponent technical AlMg9 alloy.

CONCLUSION

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