Role of Al content on the microstructure, texture and mechanical properties of Mg-3.5Ca based alloys

Abstract

Effects of Al addition (0.0, 0.5, 3.0, 7.2 wt%) on microstructure, texture and mechanical properties of Mg-3.5Ca based alloys were investigated. Our results revealed that the addition of Al to the as-cast Mg-3.5Ca alloy resulted in the transformation of precipitated secondary phase from Mg2Ca to (Mg, Al)2Ca, Al2Ca and even Mg17Al12 phase. Moreover, the as-cast microstructure evolution influenced dynamic recrystallization and texture formation in the subsequent extrusion process. As Al content increased from 0.0 to 7.2 wt%, the elongation to fracture (EL) of as-extruded Mg-3.5Ca alloy was monotonously increased from 1.9% to 9.8% in tension, while counterparts were changeless in compression. As-extruded Mg-3.5Ca-3.0Al alloy showed higher yield and ultimate strength increased by about 42.2 MPa and 71.4 MPa than those of extruded Mg-3.5Ca alloy in tension, respectively. Moreover, when Al addition was up to 7.2 wt%, both tensile yield strength and ultimate tensile strength were in steep decline. The effects of Al addition on compressive mechanical properties (compressive yield strength and ultimate compressive strength) were similar to that in tension. Especially, significantly deteriorated tension-compression asymmetry (TCA) of Mg-3.5Ca-7.2Al alloy was ascribed to grain coarsening and secondary phase transformation. Besides, Al addition also had a significant impact on the hardening capacity (Hc) and strain hardening behavior of Mg-3.5Ca alloy. In particular, as 7.2 wt% Al was added, the hardening capacity of the Mg-3.5Ca alloy was significantly increased from 0.09 to 0.56 in tension. As a result, proper Al addition to Mg-3.5Ca alloy could improve the comprehensive mechanical performance, whereas excessive Al addition not only significantly decreased the strength, but also deteriorated the TCA performance.