Effects of minor Sr additions on the as-cast microstructure, fluidity and mechanical properties of Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca (wt%) alloy

摘要

Microstructure, fluidity and mechanical properties of Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca (wt%) alloy with minor Sr contents have been investigated. All the alloys exhibited the homogeneous microstructure with equiaxed α-Mg matrix and eutectic compounds distributing along grain boundaries. The as-cast alloys are mainly composed of α-Mg phase, Mg51Zn20phase and T-phase. The fluidity of the Sr-containing Mg alloys was examined by means of the three concentric spirals mould. It was found that the fluidity of Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2 Sr alloy was effectively increased by 122.8% as compared to the quaternary alloy. This could be attributed to grain refinement as well as the reductions of oxides and melt viscosity. The Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2 Sr alloy exhibits the optimum tensile properties with ultimate tensile strength, yield strength and elongation of 144.1 MPa, 114.4 MPa and 4.9%, respectively, which is ascribed to refinement strengthening and dislocation pinning effect of T-phase. Furthermore, the fracture characteristic of Sr-containing alloys is mainly quasi-cleavage.