Aging effect of Mg-Sc alloy with α+β two-phase microstructure

Mg-20.5 at% Sc alloy with hcp (α)+bcc (β) two-phase alloy was investigated to understand the effects of aging treatment at 200°C on microstructure, hardness and tensile properties. The Mg-Sc alloy ingot was prepared by induction melting in Ar atmosphere, and then hot rolled at 600°C followed by cold rolling into a sheet. The rolled specimens were annealed at 600°C to obtain α+β two-phase microstructure. Then, the annealed specimens were aged at 200°C for various time. Vickers hardness of the α+β two-phase alloy drastically increased after a certain incubation time and then reached maximum hardness of 142.8 Hv. The incubation time of the Mg-20.5 at% Sc alloy with the α+β two-phase was longer than that of the same alloy with a β single-phase. Ultimate tensile strength (UTS) and elongation of the as-annealed specimen were 280 MPa and 28.2%, respectively. Meanwhile, the specimen aged at 200°C for 14.4 ks showed a UTS of 357 MPa and an elongation of over 12%. The specimen aged for 18 ks showed a higher UTS of 465 MPa while keeping a better elongation of 6.9%. It was found that the age hardening of the Mg-Sc alloys were attributed to the precipitation of very fine a phase in b phase.