Deformation mode and strengthening mechanism of Mg-Gd-Er-Zn-Zr alloy with different LPSO morphology

Abstract

Figuring out the effects of LPSO morphology on the deformation mode and strengthening mechanism of Mg-RE alloys is helpful to improve their formability and mechanical properties. In this work, the Mg-8Gd-1Er-1Zn-0.6Zr (GEZ811) alloys with monolithic block LPSO (B-alloy) and lamellar LPSO (L-alloy) phase were respectively prepared by different heat treatment route. The effects of the monolithic LPSO morphology on deformation mode and strengthening mechanisms during high strain rate multidirectional forging (HSMDF) were analyzed. Results showed at the initial stage of HSMDF, twinning was the dominant deformation mode for B-alloy while non-basal slip was for L-alloy. With increasing forging pass, kink band of grains became primary for B-alloy, whereas kinking and breaking of the lamellar LPSO phase was dominant for L-alloy. The optimal UTS, YS and EL of the HSMDFed B-alloy and L-alloy at 12 P were 381.6 MPa, 324.1 MPa, and 8.8 %, and 358.4 MPa, 295.0 MPa, and 5.5 %, respectively. The difference in strength between B-alloy and L-alloy resulted primarily from the contribution of grain boundary strengthening and stacking fault strengthening, while the better plasticity of B-alloy was attributed to its lower deformation activation energy and the formed kink band of grains. Retaining the block LPSO phase as much as possible in the alloy before deformation is beneficial to enhancing the mechanical performance of Mg-RE alloys.