Microstructure evolution and mechanical properties of Mg−Gd−Zn alloy with and without LPSO phase processed by multi-directional forging

Abstract

The homogenized Mg−5.6Gd−0.8Zn (wt.%) alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered (LPSO) phase. Subsequently, multi-directional forging (MDF) experiments were carried out. The microstructure and mechanical properties of different regions (the center, middle and edge regions) in the MDFed alloys were systematically investigated, and the effect of LPSO phase on them was discussed. The results show that the alloys in different regions undergo significant grain refinement during the MDF process. Inhomogeneous microstructures with different degrees of dynamic recrystallization (DRX) are formed, resulting in microhardness heterogeneity. The alloy with the LPSO phase has higher microstructure homogeneity, a higher degree of recrystallization, and better comprehensive mechanical properties than the alloy without the LPSO phase. The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties, with an ultimate compressive strength of 488 MPa, yield strength of 258 MPa, and fracture strain of 21.2%. DRX behavior is closely related to the LPSO phase and deformation temperature. The kinked LPSO phase can act as a potential nucleation site for DRX grains, while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.