Effect of multi-directional forging in a closed die after extrusion on Gd and Y added AZ61 Mg alloy

Abstract

In this study, 0.5 and 1 wt.% Gadolinium (Gd) and Yttrium (Y) rare earth elements were added to the AZ61 magnesium alloy. The alloys were exposed to extrusion at 375°C, followed by multi-directional forging in a closed die at 400°C. The microstructural changes and mechanical properties of the alloy were examined. The addition of rare earth elements and the applied mechanical processes led to a significant reduction in grain size in the AZ61 cast alloy. The addition of Gd and Y promoted the formation of the Al₂(Y,Gd) intermetallic structure, which contributed to heterogeneous nucleation and increased hardness. The extrusion and multi-directional forging processes further contributed to a fine-grained, equiaxed microstructure. As a result of the grain refinement, notable improvements in the mechanical properties were observed. In mechanical tests, samples with 0.5% Gd and 0.5% Y achieved the highest tensile strength (290 MPa) and hardness values (113 HV). In contrast, a slight decrease was observed with 1% additions, indicating that the optimal rare earth element content is 0.5%.