Effect of initial microstructure on stress-strain behavior in Mg-Sc-Zn based alloy with high Sc content

Mg-Sc-Zn based alloy was investigated to understand the effects of introducing bcc structure on mechanical properties. The alloy ingot was prepared by induction melting of ZK60 and pure Sc in Ar atmosphere, and then hot rolled at 550°C into a sheet. The rolled sheets were finally annealed at 500 (designated as a-type) and 680°C (designated as α + β-type) for 30 minutes. From XRD patterns and SEM observation, the existence of ScZn compound was confirmed in both samples. The volume fraction ratio of bcc/(hcp + bcc) were 0 and 73% on samples annealed at 500 and 680°C, respectively. The ultimate tensile strength (UTS) and elongation of the α(hcp)-type sample were 280 MPa and 20.5%, respectively, while those of α(hcp) + β(bcc)-type sample were 373 MPa and 5.9%, respectively. It was found that c/a ratio of α-type sample was small indicating that non-basal slip systems were activated during tensile test. On the other hand, it was suggested that, in β phase, the stress induced phase transformation from bcc to hcp occurred during tensile test which causes higher strength and lower elongation.