Excellent superplasticity and deformation mechanism of Al–Mg–Sc–Zr alloy processed via simple free forging

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2015-01, Vol.624, p.124-131
• Main Authors: Duan, Y.L., Xu, G.F., Xiao, D., Zhou, L.Q., Deng, Y., Yin, Z.M.
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Constitutive relationships; Deformation mechanisms; Electron back scatter diffraction; Forging; Grain boundary sliding; Intermetallic compounds; Microstructure; Quaternary systems; Superplasticity
• ISSN: 0921-5093
• DOI: 10.1016/j.msea.2014.11.054

A refined microstructure of Al-Mg-Sc-Zr alloy with an average grain size of ~3.7 mu m and a portion of high angle boundaries of 69.2% was produced by free forging. Excellent superplastic ductility of greater than or equal to 500% was achieved at a wide temperature range of 450~500 degree C and relatively high strain rate range of 110-3~510-2 s-1 in the Al-Mg-Sc-Zr alloy. A maximum elongation of 1593% was obtained at 475 degree C and 110-3 s-1. Moreover, the electron back scattered diffraction (EBSD) and the transmission electron microscopy (TEM) analyses showed that the excellent superplasticity can be attributed to the high fraction of high angle grain boundaries and the presence of Al3(Sc,Zr) dispersoids in the Al-Mg-Sc-Zr alloy microstructure. The analyses on the superplastic data revealed the presence of threshold stress, the coefficient of strain rate sensitivity of 0.5, and an activation energy of 83.9kJ/mol-1. It indicated that the dominant deformation mechanism was grain boundary sliding. Based on this notion, a constitutive equation for Al-Mg-Sc-Zr alloy has been developed.