An investigation into the hot ductility behavior of AZ81 magnesium alloy

Abstract

► Investigation of the hot ductility behavior in AZ81 alloy to characterize the ductility drops. ► Detrimental effect of grain boundary sliding on ductility values due to the resulting W-type cracks. ► DRX and CGBS as the main factor increasing the ductility at higher temperatures. ► Significant effect of γ precipitates on crack propagation in AZ81 alloy. ► The sharp ductility drop at very low strain rates due to the incipient melting of γ phase. The hot ductility behavior of AZ81 magnesium alloy, as a typical Mg–Al–Zn base cast alloy with high Al content, has been studied through applying a set of low strain rate hot tensile tests in the temperature range of 250–450 °C. The results indicated a ductility drop at 400 °C under the strain rates of 0.01 and 0.001 s −1 . This has been attributed to the occurrence of grain boundary sliding and the resulting W-type and R-type cracks at this deformation conditions. The dynamic recrystallization in large scales has been occurred and considered as the main factor increasing the ductility at higher temperatures. Under lower strain rate (0.0001 s −1 ), the ductility trough has been shifted to lower temperature (350 °C). This has been followed by an enhanced ductility regime up to 30% at 400 °C. The latter is attributed to the cooperative grain boundary sliding (CGBS) mechanism and the active grain boundary sliding of γ phase. By increasing the temperature to 450 °C the material exhibits a sharp drop in ductility variation which is explained considering the occurrence of incipient melting in this temperature range.