Hot deformation behaviour of Mg-3Al-3Sn and Mg-3Al-3Sn-1 Zn Alloys: Role of Zn

The hot deformation behaviour of two solid solution alloys Mg-3Al-3Sn (AT33) and Mg-3Al-3Sn-1 Zn (ATZ331) were investigated using processing maps approach, while elucidating the role of Zn. Processing maps were generated using the flow stress data from constant strain rate (10−3 to 10 s−1) compression testing in the temperature range of 300 to 460 °C. Three distinct common domains (Domain I, II and III) were observed in the processing maps of AT33 and ATZ331. Addition of Zn is found to have expanded the domains range in ATZ331. Compared to AT33, an additional domain (Domain IV:T∼340−380∘C,ɛ˙∼10−2−10−1s−1) is observed in ATZ331. The instability map showed instability regions in the temperature and strain rate range in which twinning was predominant. Rate controlling mechanisms were identified by correlating the activation energy (Q) and stress exponent (n) in individual domains. Flow softening mechanisms in individual domains are corroborated by correlating the post-deformed microstructures with the deformation mechanism. The Domain III (T∼400−460∘C,ɛ˙=1−10s−1) is identified as the safe hot working regime for both the alloys AT33 and ATZ331 based on the correlation of microstructural evolution together with the processing maps and kinetic analysis. Dynamic recrystallisation is a dominant flow softening mechanism in Domain I, III and IV, whereas dynamic recovery is predominant in Domain II. On the whole, Zn addition has increased the tendency for cross-slip, and resulted in more recrystallisation in Domain I besides faster recovery in Domain II as compared to AT33.