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Existing Form and Acting Mechanism of Minor Sc and Zr in Al-Mg and Al-Zn-Mg Alloys

MSE. Existing Form and Acting Mechanism of Minor Sc and Zr in Al-Mg and Al-Zn-Mg Alloys. YIN Zhi-min, JIANG Feng, PAN Qing-lin, GUO Fei-yue, ZHU Da-peng, SONG Lian-peng, ZEN Yu, WANG Tao School of Materials Science and Engineering Central South University, Changsha 410083, P. R. China.

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Existing Form and Acting Mechanism of Minor Sc and Zr in Al-Mg and Al-Zn-Mg Alloys

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  1. MSE Existing Form and Acting Mechanism of Minor Sc and Zr in Al-Mg and Al-Zn-Mg Alloys YIN Zhi-min, JIANG Feng, PAN Qing-lin, GUO Fei-yue, ZHU Da-peng, SONG Lian-peng, ZEN Yu, WANG Tao School of Materials Science and Engineering Central South University, Changsha 410083, P. R. China

  2. MSE Outline 1 Introduction 2 Experimental 3 Results and Discussion 3.1Effect of Sc, Zr on as-cast grain structures of studied alloys 3.2Behavior of Sc, Zr during homogenization treatment 3.3Effect of Sc, Zr on hot deformation structures of studied alloys 3.4Effect of Sc, Zr on recrystallization after cold-rolling 3.5Effect of Sc, Zr on microstructures of solution treated and aged studied alloys 3.6Effect of Sc, Zr on mechanical properties of studied alloys 4 Conclusion

  3. MSE Introduction 1 1.1 Classification of alloying elements in aluminum alloys ■Main alloying elements ■Minor adding elements ■Minor inpurity elements Al，Cu，Mg，Zn，...... Mn，Cr，Ti，B，Zr，V，Ag，Sc，V， ...... (Fe,Si)，K， Na，Ca，H，......

  4. MSE 1.2 Purpose of this study ■Effect of minor Sc, Zr on microstructure and mechanical properties of studied alloys ■Existing form of minor Sc, Zr in studied alloys ■Acting mechanism of minor Sc, Zr in studied alloys

  5. MSE ■Al-Mg based alloys ■Al-Zn-Mg based alloys ■Al-1.2Mg-0.4Mn//Al-1.2Mg-0.4Mn-0.4(Sc+Zr) ■Al-2.2Mg-0.4Mn// Al-2.2Mg-0.4Mn-0.4(Sc+Zr) ■Al-4.2Mg-0.4Mn//Al-4.2Mg-0.4Mn-0.4(Sc+Zr) ■Al-5.2Mg-0.4Mn//Al-5.2Mg-0.4Mn-0.4(Sc+Zr) ■Al-6.2Zn-2.0Mg//Al-6.2Zn-2.0Mg-0.35(Sc+Zr) ■Al-8.0Zn-2.5Mg-2.5Cu-Zr//Al-8.0Zn-2.5Mg-2.5Cu-(Sc+Zr) Experimental 2 2.1 Composition of studied alloys

  6. MSE 2.2 Preparation of studied alloys ■for Al-Mg based alloys(non-heat-treatable strengthening) ■for Al-Zn-Mg based alloys(heat treatable strengthening) melt cast homogenization hot-rolled cold-rolled stablizing annealing treatment melt cast homogenization hot-rolled cool-rolled aging treatment water quenching solid solution

  7. MSE 2.3 Microstructure observation ■Metallography for observing grain structure electrolylic polishing and anodizing membrane with water solution of HF and H3BO3 ■Metallography for observing crystal nucleus etched using mixed acid (1%HF+1.5%HCl+2.5%HHO3) ■Thin foils for TEM observation prepared by twinjet polishing with an electrolyte solution consisting of 30% HNO3 and 70% methanol below -25℃

  8. MSE Effect of minor Sc, Zr on as-cast grain structures of studied alloys 3.1 anodzing Fig. 1 Effect of minor Sc, Zr on as-cast structures of Al-Mg and Al-Zn-Mg based alloys a) Al-5Mg; b) Al-5Mg-0.4(Sc+Zr); c) Al-6.2Zn-2Mg; d) Al-6.2Zn-2Mg-0.35(Sc+Zr)

  9. MSE ■Dendrites disappeared ■grain size greatly decreased Al-Mg alloy:370μm→42μm Al-Zn-Mg alloy:170μm→25μm

  10. MSE etched using mixed acid Fig. 2 Mechanism analysis of minor Sc, Zr refining as-cast grains a) Al-5Mg-0.4(Sc+Zr); b) Al-6.2Zn-2Mg-0.35(Sc+Zr); c-d) electron microprobe analysis of particles in Fig. 2a)

  11. MSE ~ ~ ■SEM/EDS (in at-% ) Zr rich in the center Sc rich in the shell Al : (Sc+Zr) 3 : 1 Particles within the grain can be discribed as: Al3(Sc,Zr) or Al3Sc/Al3Zr Al3Sc/Al3Zr is an ideal hetergeneous crystal nucleus

  12. MSE Behavior of minor Sc, Zr during homogenization treatment 3.2 Fig .3 Microstructure of Al-5Mg-0.4(Sc+Zr) alloys after 470℃/13h homogenization treatment a)Bright field imageof Al3(Sc,Zr)II;b)SEAD pattern; c-d)Dark field imageof Al3(Sc,Zr)II

  13. MSE ■Al3(Sc,Zr) precipitating from α(Al) solid solution ■Al3(Sc,Zr), 5~8nm in size ■Composite particles Al3Sc/Al3Zr ■Coherent to the matrix

  14. MSE Effect of minor Sc, Zr on hot deformation structures of studied alloys 3.3 a-b) OM c-d) TEM e-f) OM Fig .4 Effect of minor Sc, Zr on hot-rolled structures of studied alloys a) Al-5Mg; b-d) Al-5Mg-0.4(Sc+Zr); e) Al-6.2Zn-2Mg; f) Al-6.2Zn-2Mg-0.35(Sc+Zr)

  15. MSE ■Recrystallization was completedly prohibited ■Dislocation and subgrain boundaries were pinned by Al3Sc/Al3Zr

  16. MSE Effect of minor Sc, Zr on recrystallization after cold-rolling 3.4 Fig .5 The relationship between hardness and annealing temperature a) Al-5Mg-0.4(Sc+Zr) alloy; b) Al-6.2Zn-2Mg-0.35(Sc+Zr) alloy

  17. MSE ■Starting recrystallization temperature Al-Mg alloy:225oC→425oC Al-Zn-Mg alloy: 355oC→535oC ■Ending recrystallization temperature Al-Mg alloy:380oC→570oC Al-Zn-Mg alloy:450oC→620oC, near melting point

  18. MSE Fig .6 Microstructures of cold-rolled plates at different annealing temperatures a-b)Al-5Mg-0.4(Sc+Zr) alloy, 400℃/1h; c-d)Al-6.2Zn-2Mg-0.35(Sc+Zr) alloy,535℃/1h

  19. MSE Effect of minor Sc, Zr on microstructures of solution treated and aged studied alloys 3.5 Fig .7 TEM microstructure of studied alloys at different treated conditions a)Al-6.2Zn-2Mgalloy, as-solution treated; b-c) Al-6.2Zn-2Mg-0.35(Sc+Zr)alloy, as-solution treated; c) (001) dark field image of Al3(Sc,Zr)II particles; d) Al-6.2Zn-2Mg alloy, 120℃/12h aging; e) Al-6.2Zn-2Mg-0.35(Sc+Zr)alloy, 120℃/12h aging; f) [001] SAED pattern of Fig. 2e)

  20. MSE MgZn2 precipitation in Al-Zn-Mg alloy with and without minor Sc, Zr have no much difference, suggesting that minor Sc and Zr have little effect on precipitation of MgZn2.

  21. MSE Effect of minor Sc, Zr on mechanical properties of studied alloys 3.6 Table 1 Tensile properties of different treated Al-5Mg and Al-5Mg-0.4(Sc+Zr) alloys

  22. MSE Table 2 Tensile properties of different treated Al-6.2Zn-2Mg and Al-6.2Zn-2Mg-0.4(Sc+Zr) alloys

  23. MSE ■Adding of 0.4(Sc+Zr) to Al-5Mg, σb : ↑96MPa, σ0.2 :↑73MPa, δ : 18→15 ■Adding of 0.35(Sc+Zr) to Al-6.2Zn-2Mg,σb:↑97MPa, σ0.2:↑104MPa, δ: 12.9→10.6 Minor element alloying is an effective way to strengthening and toughing of aluminum alloys

  24. MSE Conclusions 4 ■Adding of minor Sc and Zr to Al-Mg and Al-Zn-Mg based alloy greatly increases the strength of the alloy by 25%, while the ductility can remain 15% and 8%, respectively

  25. MSE ■ In Al-Mg and Al-Zn-Mg based alloys, minor Sc and Zr mainly exist in two forms of aluminides containing Sc and Zr, one is Al3(Sc,Zr)I precipitating from the melt during solidification,the other is Al3(Sc, Zr)II precipitating during homogenization. The former is the most effective grain refiner for α(Al) solid solution matrix, and the latter is coherent with the matrix, strongly pinning dislocations and subgrain boundaries, which can effectively restrain recrystallization during hot deformation, annealing and solid solutioning of the alloys

  26. MSE ■ Strengthening increment caused by adding of minor Sc and Zr ro Al-Mg and Al-Zn-Mg based alloys is mainly due to fine-grain strengthening, precipitation strengthening and substructure strengthening of Al3(Sc,Zr)II caused by restraining recrystallization

  27. MSE Thank you

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