Effects of Ti addition on the microstructure and mechanical properties of Mg–Zn–Zr–Ca alloys

Replacing the RE element with Ti can reduce the cost.New ternary phase is formed at grain boundary.Ti can be used to refine α-Mg grains in the Mg–Zn–Zr based alloy.The alloy containing 0.80 wt.% Ti can be developed to serve at elevated temperature as engine block.

The effects of Ti additions (0, 0.4, 0.6, 0.8, 1.0, 1.2 wt.%) on the microstructure and mechanical properties of as-cast and aging Mg-0.4%Zn-1.0%Zr-1.5%Ca (wt.%) alloys were investigated. The results indicated that minor Ti can effectively refine grains, while excessive Ti addition resulted in the grain coarsening. When the content of Ti was 0.8 wt.%, the as-cast alloy exhibited the finest grain size of 39 μm which contributed to the optimal mechanical properties with Brinell hardness of 57.9 HB, ultimate tensile strength of 145 MPa and elongation of 3.2%. After T6 heat treatment, the continuous net-like Mg2Ca and Mg6Zn3Ca2 phases changed to uniform massive T phases (ternary Mg–Zn–Ca phases) and dispersive halo-like precipitates (Mg2Ca and Mg6Zn3Ca2 phases). The ultimate tensile strengths of the alloy at room temperature (RT), 175 °C and 200 °C were correspondingly improved to 182 MPa, 169 MPa and 141 MPa, respectively.