1. 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 A Novel Approach for Acquiring Thermodynamic Database of Al Alloys and Investigation of Microstructure during Solidification of Al Alloys  The 3 rd International Symposium Light Metals and Composite Materials, Belgrade, Serbia, September 12-14, 2008.  Celebration of the 200th Anniversary of University of Belgrade

2. 2 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

3. 3 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. Al-based alloys 1. Motivation

4. 4 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

5. 5 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) Point analysis for phase compositions Area scan for solute redistribution in (Al) SEM/EDX (Image) Fraction of phase 2. Experimental and computational approaches

6. 6 Fig. 1. Phase equilibria of the Al-Ni-Zn system at 1100 ℃ determined by diffusion couple technique and equilibrated alloys 2. Experimental and computational approaches Diffusion couple technique + equilibrated alloys

7. 7 AlSiNi phase transition temperatures  Composition range of the primary phases  Crystal structure  isothermal section Liquidus surface and reaction scheme for the ternary system XRD, EPMA, DTA annealed at 550 o C for 1 month Arc-melting Metallography EDX,EPMA 30 ternary alloys 3.Experimental procedure 2. Experimental and computational approaches As-cast Fig. 2. Experimental procedure to establish reaction scheme of the Al-Ni-Si system

8. 8 Calorimetry: Measurement of enthalpy of formation Kleppa high temperature calorimeter aAl (298K) + bNi (298K) + cX (298K)= Al a Ni b X c (1473 K) aAl (298K) + bNi (298K) + cX (298K)= Al a Ni b X c (1473 K)  H reaction (1) Al a Ni b X c (298 K) = Al a Ni b X c (1473 K)  H heat content (2) (1) - (2) get: (1) - (2) get: aAl (298K) + bNi (298K) + cX (298K) = Al a Ni b X c (298 K) aAl (298K) + bNi (298K) + cX (298K) = Al a Ni b X c (298 K) (3) Samples preparation Procedure (two steps) Al X Ni MixingPressing Elemental powder Sample pellets Deoxidization 2. Experimental and computational approaches Fig. 3. Procedure to measure the enthalpy of formation via calorimetry

9. 9 CALPHAD Method Gibbs energy at reference states Ideal entropy of mixing Excess Gibbs energy Magnetic contributions to the Gibbs energy 2. Experimental and computational approaches Fig. 5. Procedure of CALPHAD method

10. 10  VASP-Vienna Ab Initio Simulation Package  Physical Fundamental: Density Function Theory First principles calculation  theory ： DFT  Base set ： Plane Waves  Pseudopotential ： UltraSoft Pseudopotential Projector Augmented Wave method  Exange and correlation ： LDA, GGA, LDA + U Total energy T[n]: Kinetic Energy E H :Hartree Energy(e-e repulsion) E xc : Exchange and correlation energies V(r) :External potential  Enthalpy of formation of AlNi2Si 2. Experimental and computational approaches

11. 11 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

12. 12 Thermodynamic database for the Al-Fe-Mg-Mn-Si-Cu-Ni-Zn system 28 binary system 56 ternary systems 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

13. 13 The following phases are included in the modeling: Thermodynamic 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. Fcc_A1 Fcc_L1 2 Bcc_A2 Bcc_B2 3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system

14. 14 Thermodynamic modeling Thermo-calc software accepts 1000 experimental data; Measured sections at 550, 800 and 1000 o C 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. 80 70 60 50 40 30 20 10 0 Ni Al Si 3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system

15. 15 The Al-Ni-Si ternary system Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612. (a) (b) Fig. 6. Calculated isothermal sections with the experimental data at (a) 1000 and (b) 800 o C Calculated isothermal sections

16. 16 The Al-Ni-Si ternary system (a) Fig. 7. Calculated isothermal sections with the experimental data at (a) 750 and (b) 550 o C (b) Calculated isothermal sections Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

17. 17 Fig. 8. Model-predicted vertical sections with the experimental data. (a) 80 at.% Ni; (b) 75 at.% Ni The Al-Ni-Si ternary system (a) (b) Model predicted vertical sections Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

18. 18 The Al-Ni-Si ternary system Fig. 9. Model-predicted vertical sections with the experimental data. for 66.67 at.% Ni (a) CALPHAD predicted; (b) experimental constructed (a) (b) Model predicted vertical sections Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

19. 19 The Al-Ni-Si ternary system Fig. 10. Model-predicted vertical sections with the experimental data. (a) 60 at.% Ni; (b) 55 at.% Ni (a) (b) Model predicted vertical sections Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

20. 20 Fig. 11. Model-predicted vertical sections with the experimental data. (a) 50 at.% Ni; (b) 45 at.% Ni The Al-Ni-Si ternary system (a) (b) Model predicted vertical sections Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

21. 21 (a) The Al-Ni-Si ternary system Fig. 12. Model-predicted vertical sections with the experimental data. (a) 40 at.% Ni; (b) 30 at.% Ni (b) Model predicted vertical sections Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

22. 22 The Al-Ni-Si ternary system Fig. 13. Model-predicted vertical sections with the experimental data. (a) 20 at.% Ni; (b) 10 at.% Ni (a) (b) Model predicted vertical sections Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

23. 23 Table 1. Calculated enthalpy of formation for AlNi 2 Si (kJ/mole-atoms) CompositionCALPHADExperimentVASP AlNi 2 Si–55.00–56.43–56.36 Enthalpy of meltingCALPHADExperiment* L = Al3Ni + (Al) + (Si)–14.13–12.22 * DSC measurement (N.M. Martynova et al., Russ. J. Phys. Chem. 58 (1984) 616 – 617. Table 2. Enthalpy of melting for the invariant eutectic L = Al3Ni + (Al) + (Si) (kJ/mole-atoms) The Al-Ni-Si ternary system Model predicted thermodynamic properties Wei Xiong, Yong Du et al., Int. J. Mater. Res. 99 (2008) 598-612.

24. 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

25. 25 Thermodynamic database Kinetic database Real solidification condition 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 3.2 Solidification behaviors of Al356.1 alloy

26. 26 L  (Al) : Calculated- 615 o C, Measured-616 o C L  (Al)+(Si)+α-AlMnSi : Calculated - 573 o C, Measured -575 o C Fig. 14. The DSC curve of equilibrium solidification of multi-component Al 356.1 alloy (∆T=3 o C) Equilibrium Solidification: Equilibrium Solidification: Complete diffusion in both liquid and solid phases Al356.1 is annealed at 550 o C for 45 days 3.2 Solidification behaviors of Al356.1 alloy

27. 27 Table 3. The comparison between the non-equilibrium calculation and the experimental solidification of multi-component Al 356.1 alloy ( ∆T=6 o C) Scheil model calculation Scheil model calculation Measured [1990Bae] L  (Al) at 615 o C L  (Al) at 614 o C L  (Al) +  -AlMnSi at 588 o C L  (Al) +  -AlMnSi at 594 o C L  (Al) + (Si) +  -AlNiSi +  -AlMnSi at 572 o C L  (Al) + (Si) +  -AlNiSi at 575 o C L  (Al) + (Si) + Mg 2 Si +Al 8 NiMg 3 Si 6 +  -AlMnSi at 556 o C L  (Al) + (Si) + Mg 2 Si + Al 8 NiMg 3 Si 6 at 554 o C Scheil model: Scheil model: No diffusion in solid phase, complete diffusion in liquid 1990Bac: L. Bäckerud et al., Solidification Characteristics of Aluminum Alloys, Vol. 2, Foundry Alloys, AFS/Skanaluminium, Sweden (1990). 3.2 Solidification behaviors of Al356.1 alloy

28. 28 Fig. 15. Microstructure (directional solidification with a cooling rate of 2K/S) Micromodel: 3.2 Solidification behaviors of Al356.1 alloy complete diffusion in liquid back diffusion in solid phases undercooling

29. 29 Cylindrical model Scheil model Experiment Sphere model Secondary dendrite: sphere, cylinder (I) Diffusion in solid phase; (II)The growth of dendirte; (III)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) 3.2 Solidification behaviors of Al356.1 alloy Micromodel:

30. 30 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

31. 31 A thermodynamic database of Al-Fe-Mg-Mn-Si-Cu-Ni-Zn- (+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. 4. Summary

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34. 34 Prof. Dr. Yong Du State Key Lab of Powder Metallurgy Central South University Changsha, Hunan, 410083, P.R. China E-mail: yongduyong@gmail.com Fax: +86-731-8710855 http://www.imdpm.net Thank you for your attention! Welcome to China! Thank you for your attention! Welcome to China!