Research On Al-Mg-Sc And Al-Mg-Er Alloys’Superplastic Capability

The superplasticity of Al-6Mg-0.4Mn-0.10Sc-0.12Zr and Al-6Mg-0.4Mn-0.25Er-0.12Zr alloys sheet was investigated. The results shown both alloys exhibited superplasticity during tensile in the temperature range of400-540℃and strain rate range of1.67×10"4to1.67×10-1s-.Scanning electron microscope inspection was performed to study two alloys’fracture morphology. Cavitations were detected by metallurgical microscope. The typical microstructure of dynamic recrystallization were observed by TEM. The present work demonstrated that:1) Through the high-temperature superplastic tensile experiment, in the same temperature and initial strain rate superplastic deformation, the rupture elongation of Al-Mg-Mn-Sc-Zr alloy is higher than Al-Mg-Mn-Er-Zr alloy though both of them perform superplasticity. Al-Mg-Mn-Sc-Zr alloy got the maximum elongation673%under the conditions of540℃,1.67×10-3s-1, whereas Al-Mg-Mn-Er-Zr alloy got the maximum elongation342%under the conditions of540℃and1.67×10-4s-12) The strain rate sensitively index m of two kinds of alloy is measured by the slope method. From low temperature400℃to high temperature540℃, the strain rate sensitively index m of Al-Mg-Mn-Sc-Zr alloy were0.300～0.316; and the strain rate sensitively index m of Al-Mg-Mn-Er-Zr alloy were0.251-0.297. The average activation energy of Al-Mg-Sc alloy was121.7kJ/mol, which was less than that of and Al-Mg-Er alloy of which was159.4kJ/mol.3) After1h annealing at350℃, both of the alloys occur recovery in a certain degree. Alloys with Sc can partly keeping processing state fibrous tissue a, while alloy with Er begin to recrystallize. The addition of Sc element is more likely to resist recrystallization than Er.4) The fracture mode of two alloys belongs to intergranular fracture. Significant cavitations are observed in the samples which are mainly distributed along the stretching direction. And the cavitation size and volume fraction increase with the deformation increasing.5) Better superplasticity of Sc-containing alloy was attributed to presence of Al3(Sc, Zr) dispersoids, which can inhibit recrystallization and grain growth effectively. The main mechanism of superplastic deformation of the two alloys is grain boundary sliding and grain rotation accommodated by dynamic recrystallization, dislocation motion, grain boundary diffusion, liquid phase, filament and cavity.