Effect of extrusion parameters on microstructure and mechanical properties of Mg-7.5Gd-2.5Y-3.5Zn-0.9Ca-0.4Zr (wt%) alloy

Abstract

As-cast Mg-7.5Gd-2.5Y-3.5Zn-0.9Ca-0.4Zr (wt%) alloy was indirectly extruded using different parameters. The microstructure, texture and mechanical properties of the as-extruded alloys were investigated. Hot extrusion effectively refines the microstructure and fragments the coarse phases in the as-cast alloy. The alloys extruded at 400°C exhibit bimodal microstructure comprising fine dynamically recrystallized (DRXed) grains with weak basal texture and coarse worked grains with strong basal fiber texture. DRX process is promoted by increasing extrusion ratio. Extrusion at high temperatures of 450°C and 500°C leads to complete DRX and weak basal fiber texture. In addition, DRXed grain growth occurs and an unusual texture with basal planes perpendicular to extrusion direction appears. The alloy extruded at 400°C and ratio of 10:1 shows the tensile yield strength of 345MPa, ultimate tensile strength of 405MPa and elongation to failure of 8.8%. The strength decreases but elongation increases with increasing extrusion ratio and temperature, while the strain hardening capacity is improved due to the higher concentration of solute atom dissolved in the matrix, fewer dislocations and larger DRXed grain size.