Effects of deformation temperatures on microstructures, aging behaviors and mechanical properties of Mg-Gd-Er-Zr alloys fabricated by hard-plate rolling

In this investigation, the high-strength Mg-12Gd-1.0Er-0.5Zr (wt.%) alloy sheets were produced by hot extrusion (HE) and subsequent hot rolling (HR) at different temperatures. The results indicate that microstructures of these final-rolled sheets are inhomogeneous, mainly including coarse deformed grains and dynamic recrystallized (DRXed) grains, and the volume fraction of these coarse deformed grains increases as the rolling temperature increases. Thus, more DRXed grains can be found in R-385 °C sheet, resulting in smaller average grain size and weaker basal texture, while the biggest grains and highest strong basal texture are present in R-450 °C sheet. Amounts of dynamic precipitation of β phase which are mainly determined by the rolling temperature are present in these sheets, and its precipitation will consume the content of Gd solutes in matrix. As a result, the lowest number density of β phase in R-450 °C sheet is beneficial to modify the aging hardening response. Thus, the R-450 °C sheet displays the best aging hardening response because of a severe traditional precipitation of β' (more) and β H / β M (less) phases densely, which resulting in a sharp improvement in strength, i.e. ultimate tensile strength (UTS) of ~ 518 MPa and yield strength (YS) of ~ 438 MPa. However, the elongation (EL) of this sheet reduces greatly, and its value is ~ 2.7%. By contrasting, the EL of the peak-aging R-385 °C sheet keeps better, which decreases from ~ 4.9% to ~ 4.8% due to a dislocation-induced novel chain-like precipitates, which is good for keeping good balance between strength and ductility.