Compositional optimization of Mg–Zn–Sc sheet alloys for enhanced room temperature stretch formability

Abstract

Effects of scandium (Sc) content on microstructures and mechanical properties of a Mg–1.5Zn (wt.%) alloy have been systematically investigated. Mg–1.5Zn alloys with Sc content no more than 0.3 wt% showed large index Erichsen (I.E.) values, an indicator of stretch formability, over than 8 mm due to weak basal textures. Further increase in Sc content up to 1.5 wt% led to a gradual decline in the stretch formability and a Mg–1.5Zn–1.5Sc alloy showed the lowest I.E. value of 4.2 mm. Detailed microstructural characterization of the Mg–1.5Zn–1.5Sc alloy revealed that the poor stretch formability was associated with a combined effect of strong basal texture, un-recrystallized matrix grains and a dense distribution of ScZn and Sc second phase particles. On the other hand, tensile properties, in particular tensile yield strength (TYS) and r-value were almost identical along the rolling direction (RD) and the transverse direction (TD) for a Mg–1.5Zn–0.1Sc alloy. Higher TYS and r-value along the RD than the TD were observed in a Mg–1.5Zn–0.3Sc alloy, while opposite results were obtained in Mg–1.5Zn–1.0Sc and Mg–1.5Zn–1.5Sc alloys. Different plastic anisotropy trends observed in Mg–1.5Zn–xSc (x = 0.1–1.5) alloys could be ascribed to their distribution of crystallographic orientations.