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Yong Du , W.W. Zhang, W. Xiong State Key Lab of Powder Metallurgy, Central South University, China

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

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Yong Du , W.W. Zhang, W. Xiong State Key Lab of Powder Metallurgy, Central South University, China

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  1. 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

  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. Al-based alloys 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.

  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. Point analysis for phase compositions Area scan for solute redistribution in (Al) 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

  6. 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

  7. 2. Experimental and computational approaches • Experimental procedure Al Ni Si 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

  8. 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

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

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

  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. 3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system Thermodynamic database for the Al-Fe-Mg-Mn-Si-Cu-Ni-Zn 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

  13. Fcc_A1 Fcc_L12 Bcc_A2 Bcc_B2 3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system Thermodynamic modeling 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_A1and Fcc_L12.

  14. Ni 80 70 60 50 40 30 20 10 0 Si Al 3.1 Thermodynamic data of Al alloys: case study for the Al-Ni-Si system Thermodynamic modeling • 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.

  15. The Al-Ni-Siternary system Calculated isothermal sections (b) (a) 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.

  16. The Al-Ni-Siternary system Calculated isothermal sections (b) (a) 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-Siternary system Model predicted vertical sections (b) (a) 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-Siternary 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-Siternary system Model predicted vertical sections (b) (a) 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-Siternary system Model predicted vertical sections (b) (a) 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-Siternary system Model predicted vertical sections (b) (a) 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-Siternary system Model predicted vertical sections (b) (a) 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-Siternary 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

  25. 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

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

  27. Scheil model calculation Measured [1990Bae] L  (Al) at 615 oC L  (Al) at 614 oC L  (Al) + -AlMnSi at 588 oC L  (Al) + -AlMnSi at 594 oC L  (Al) + (Si) +  -AlNiSi + -AlMnSi at 572 oC L  (Al) + (Si) +  -AlNiSi at 575 oC L  (Al) + (Si) + Mg2Si + Al8NiMg3Si6 at 554 oC L  (Al) + (Si) + Mg2Si +Al8NiMg3Si6+-AlMnSi at 556 oC 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(∆T=6oC) 1990Bac:L. Bäckerud et al., Solidification Characteristics of Aluminum Alloys, Vol. 2, Foundry Alloys, AFS/Skanaluminium, Sweden (1990).

  28. 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)

  29. Experiment Sphere model Scheilmodel Cylindrical model 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)

  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. 4. Summary • 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.

  32. 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@gmail.com Fax: +86-731-8710855 http://www.imdpm.net

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