Yong Du, W'W' Zhang, W' Xiong

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A Novel Approach for Acquiring Thermodynamic
Database of Al Alloys and Investigation of
Microstructure during Solidification of Al Alloys
Yong Du, W.W. Zhang, W. Xiong State Key Lab of
Powder Metallurgy, Central South University,
China R.X. Hu, P. Nash Thermal Processing
Technology Center, Illinois Institute of
Technology, USA
?The 3rd International Symposium Light Metals and
Composite Materials, Belgrade, Serbia, September
12-14, 2008. ?Celebration of the 200th
Anniversary of University of Belgrade
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Contents

• 1. Motivation
• 2. Experimental and computational approaches
• 3. Results and discussion
• 3.1 Thermodynamic data of Al alloys case
  study for the Al-Ni-Si system
• 3.2 Solidification behaviors of Al356.1 alloy
• Equilibrium solidification
• Scheil model
• Mircomodel
• 4. Summary

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1. Motivation

• Al-based alloys are widely used as aeronautic
  and civil materials
• Among many commercial alloys (Al-, Fe-, Ni-,
  Mg-based etc. alloys), only Fe-based
  thermodynamic database is well established by
  Thermo-calc company, Sweden.
• Currently Lack of reliable thermodynamic and
  kinetic databases for Al alloys!
• Our work (I) to establish thermodynamic and
  kinetic databases for multi-
  component
  Al alloys via a hybrid approach of experiment,
  CALPHAD and first-principles methods
• (II) to describe the
  microstructure and micro-segregation during
  solidifications of Al alloys using thermodynamic
  and kinetic databases.

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Contents

• 1. Motivation
• 2. Experimental and computational approaches
• 3. Results and discussion
• 3.1 Thermodynamic data of Al alloys case
  study for the Al-Ni-Si system
• 3.2 Solidification behaviors of Al356.1 alloy
• Equilibrium solidification
• Scheil model
• Mircomodel
• 4. Summary

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2. Experimental and computational approaches

• 2.1 Experimental approach
• Phase diagram measurement
• Equilibrated alloys, diffusion couple, XRD,
  EPMA, DTA, DSC, SEM
• Measurement of enthalpy of formation and heat
  capacity
• Directional solidification
• Temperature gradient 45K/cm Growth rate
  0.04445cm/s
• XRD, EPMA
• 2.2 Computational approach
• CALPHAD method (thermodynamic modeling)
• First-principles method (Enthalpy of formation
  computation)
• Molecular dynamics (Diffusion coefficient
  caculation)

SEM/EDX (Image) Fraction of phase
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2. Experimental and computational approaches
Diffusion couple technique equilibrated alloys
Fig. 1. Phase equilibria of the Al-Ni-Zn system
at 1100? determined by diffusion couple technique
and equilibrated alloys
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2. Experimental and computational approaches
Al
Si
Ni

• Experimental procedure

Arc-melting
30 ternary alloys
As-cast
annealed at 550oC for 1 month
Metallography EDX,EPMA
DTA
XRD, EPMA,
?Crystal structure ? isothermal section

• phase transition temperatures

? Composition range of the primary phases
Liquidus surface and reaction scheme for the
ternary system
Fig. 2. Experimental procedure to establish
reaction scheme of the Al-Ni-Si system
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2. Experimental and computational approaches
Calorimetry Measurement of enthalpy of formation
Kleppa high temperature calorimeter

• Samples preparation

Elemental powder
Sample pellets
Al
Mixing
Pressing
Ni
X
Deoxidization

• Procedure (two steps)

aAl (298K) bNi (298K) cX (298K) AlaNibXc
(1473 K)
?Hreaction (1) AlaNibXc (298
K) AlaNibXc (1473 K)
?Hheat
content (2) (1) - (2) get aAl (298K)
bNi (298K) cX (298K) AlaNibXc (298 K) (3)
Fig. 3. Procedure to measure the enthalpy of
formation via calorimetry
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2. Experimental and computational approaches
CALPHAD Method
Fig. 5. Procedure of CALPHAD method
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VASP-Vienna Ab Initio Simulation Package
2. Experimental and computational approaches
First principles calculation

• Physical Fundamental Density Function Theory

Total energy
Tn Kinetic Energy EHHartree
Energy(e-e repulsion) Exc Exchange and
correlation energies V(r) External potential

• theoryDFT
• Base setPlane Waves
• PseudopotentialUltraSoft Pseudopotential
• Projector Augmented
  Wave method
• Exange and correlationLDA, GGA, LDA U

• Enthalpy of formation of AlNi2Si

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Contents

• 1. Motivation
• 2. Experimental and computational approaches
• 3. Results and discussion
• 3.1 Thermodynamic data of Al alloys case
  study for the Al-Ni-Si system
• 3.2 Solidification behaviors of Al356.1 alloy
• Equilibrium solidification
• Scheil model
• Mircomodel
• 4. Summary

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Thermodynamic database for the Al-Fe-Mg-Mn-Si-Cu-N
i-Zn system
3.1 Thermodynamic data of Al alloys case study
for the Al-Ni-Si system
?Al-Fe, Al-Fe-Zn etc. Literature ?Al-Mn, etc.
Present work (finished) ?Mn-Si-Cu, etc. in
progress
28 binary system 56 ternary systems
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Thermodynamic modeling
3.1 Thermodynamic data of Al alloys case study
for the Al-Ni-Si system
The following phases are included in the modeling
A symmetric model (Al,Ni,Si,Va)0.5(Al,Ni,Si,Va)0.5
for A2 and B2 and the one (Al,Ni,Si)0.75(Al,Ni,Si
)0.25 for Fcc_A1 and Fcc_L12.
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Thermodynamic modeling
3.1 Thermodynamic data of Al alloys case study
for the Al-Ni-Si system
Thermo-calc software accepts 1000 experimental
data Measured sections at 550, 800 and 1000
oC plus 13 vertical sections with 22 invariant
equilibria 2003Ric, 2004Ric, 2006Cha, this
work 3000 experimental data Only key
experimental data are used three isothermal
sections and 22 invariant reactions
Key References 2003Ric K.W. Richter, H.
Ipser Intermetallics 11 (2003) 101
109. 2004Ric K.W. Richter, K.
Chandrasekaran, H. Ipser Intermetallics 12
(2004) 545 554. 2006Cha K. Chandrasekaran,
K.W. Richter, H. Ipser Intermetallics 14 (2006)
491 497.
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The Al-Ni-Si ternary system
Calculated isothermal sections
(a)
(b)
Fig. 6. Calculated isothermal sections with the
experimental data at (a) 1000 and (b) 800 oC
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
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The Al-Ni-Si ternary system
Calculated isothermal sections
(a)
(b)
Fig. 7. Calculated isothermal sections with the
experimental data at (a) 750 and (b) 550 oC
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
17
The Al-Ni-Si ternary system
Model predicted vertical sections
(a)
(b)
Fig. 8. Model-predicted vertical sections with
the experimental data. (a) 80 at. Ni (b) 75
at. Ni
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
18
The Al-Ni-Si ternary system
Model predicted vertical sections
(b)
(a)
Fig. 9. Model-predicted vertical sections with
the experimental data. for 66.67 at. Ni (a)
CALPHAD predicted (b) experimental constructed
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
19
The Al-Ni-Si ternary system
Model predicted vertical sections
(a)
(b)
Fig. 10. Model-predicted vertical sections with
the experimental data. (a) 60 at. Ni (b) 55
at. Ni
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
20
The Al-Ni-Si ternary system
Model predicted vertical sections
(a)
(b)
Fig. 11. Model-predicted vertical sections with
the experimental data. (a) 50 at. Ni (b) 45
at. Ni
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
21
The Al-Ni-Si ternary system
Model predicted vertical sections
(a)
(b)
Fig. 12. Model-predicted vertical sections with
the experimental data. (a) 40 at. Ni (b) 30
at. Ni
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
22
The Al-Ni-Si ternary system
Model predicted vertical sections
(a)
(b)
Fig. 13. Model-predicted vertical sections with
the experimental data. (a) 20 at. Ni (b) 10
at. Ni
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
23
Table 1. Calculated enthalpy of formation for
AlNi2Si (kJ/mole-atoms)
The Al-Ni-Si ternary system
Model predicted thermodynamic properties
Table 2. Enthalpy of melting for the invariant
eutectic L Al3Ni (Al) (Si) (kJ/mole-atoms)
DSC measurement (N.M. Martynova et al., Russ.
J. Phys. Chem. 58 (1984) 616 617.
Wei Xiong, Yong Du et al., Int. J. Mater. Res.
99 (2008) 598-612.
24
Contents

• 1. Motivation
• 2. Experimental and computational approaches
• 3. Results and discussion
• 3.1 Thermodynamic data of Al alloys case
  study for the Al-Ni-Si system
• 3.2 Solidification behaviors of Al356.1 alloy
• Equilibrium solidification
• Scheil model
• Mircomodel
• 4. Summary

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3.2 Solidification behaviors of Al356.1 alloy
Thermodynamic database
Real solidification condition
Kinetic database

• Kinetic database input
• Impurity diffusivity of Ni, Mg, Mn, Si in
  liquid Al and solid (Al)
• Energy of solid/liquid interface
• Specific latent heat of solidification
• Geometric factor for coarsening

Liquid
Solid
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3.2 Solidification behaviors of Al356.1 alloy

• Equilibrium Solidification Complete diffusion
  in
• both liquid and solid phases

L ? (Al) Calculated- 615oC, Measured-616 oC L
? (Al)(Si)a-AlMnSi Calculated- 573oC,
Measured-575 oC
Al356.1 is annealed at 550oC for 45 days
Fig. 14. The DSC curve of equilibrium
solidification of multi-component Al 356.1 alloy
(?T3 oC)
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3.2 Solidification behaviors of Al356.1 alloy

• Scheil model No diffusion in solid phase,
• complete diffusion in liquid

Table 3. The comparison between the
non-equilibrium calculation and the experimental
solidification of multi-component Al 356.1 alloy
(?T6oC)
1990Bac L. Bäckerud et al., Solidification
Characteristics of Aluminum Alloys, Vol. 2,
Foundry Alloys, AFS/Skanaluminium, Sweden (1990).
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3.2 Solidification behaviors of Al356.1 alloy

• complete diffusion in liquid
• back diffusion in solid phases
• undercooling

Micromodel
Fig. 15. Microstructure (directional
solidification with a cooling rate of 2K/S)
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3.2 Solidification behaviors of Al356.1 alloy
Micromodel

• Secondary dendrite sphere, cylinder
• (I) Diffusion in solid phase
• The growth of dendirte
• Solute super-cooling,
• temperature gradient super-cooling

Yong Du et al., Z. Metallkd., 96, 1351-1362 (2005)
Fig. 16. Si distribution in the primary (Al)
during the directional solidification of
multi-component Al 356.1 alloy (Cooling rate
2K/S)
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Contents

• 1. Motivation
• 2. Experimental and computational approaches
• 3. Results and discussion
• 3.1 Thermodynamic data of Al alloys case
  study for the Al-Ni-Si system
• 3.2 Solidification behaviors of Al356.1 alloy
• Equilibrium solidification
• Scheil model
• Mircomodel
• 4. Summary

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4. Summary

• A thermodynamic database of Al-Fe-Mg-Mn-Si-Cu-Ni-Z
  n-(more elements) system is being constructed
• A kinetic database of Al-Fe-Mg-Mn-Si-Cu-Ni-Zn
  system is being constructed
• Hybrid approach Key experiment CALPHAD
  First-principles method
• The thermodynamic and kinetic database are used
  to describe the solidification behaviors of Al
  alloys.

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Thank you for your attention! Welcome to China!
Prof. Dr. Yong Du State Key Lab of Powder
Metallurgy Central South University Changsha,
Hunan, 410083, P.R. China E-mail
yongduyong_at_gmail.com Fax [phone] http//w
ww.imdpm.net