Grain Refinement and Aging Hardening of the Mg-10Gd-3Y-2Ag-0.4Zr Alloy Produced by a Two-Step Forming Process

Grain refinement and precipitation are two effective ways to improve the mechanical properties of Mg-RE alloys. In this work, a two-step forming process is proposed. This includes cold rolling and subsequent annealing at high temperature for a short duration. By the two-step forming process, grains can be refined from 100 μm to 20 μm in compare with ~30 μm by common hot rolling at 450 °C for a reduction of 80%. The sample shows more distinct aging hardening, as the hardness amplification of 60 HV is twice that of the hot-rolled sample. The precipitation is observed by high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). Dynamic precipitation in the sample by the two-step route is found to be effectively suppressed. Interestingly, after subsequent annealing, the density of precipitation, especially β′, become much higher than that in hot-rolled samples.