Effect of Ca content on mechanical properties and ignition resistance of Mg−Zn−Zr−Ca alloys
The ignition vulnerability of magnesium alloys restricts their deployment in high-temperature aerospace and railway applications. This study investigates the influence of calcium content (0, 0.6, 1.2, 1.8 wt.%) on the microstructure, mechanical properties, and ignition resistance of gravity-cast and hot-extruded Mg−6Zn−0.6Zr alloys. Calcium addition promotes the formation of Ca2Mg6Zn3 phases while suppressing MgZn2 precipitation in the as-cast condition. Homogenization dissolves most MgZn2 phases but retains numerous Ca2Mg6Zn3 particles. Subsequent extrusion fragments the Ca2Mg6Zn3 phases and precipitates nanoscale MgZn2 within the matrix. The synergy of fine grains and high-density precipitates substantially enhances strength. The Mg−6Zn−0.6Zr−1.2Ca alloy achieves optimal mechanical performance, with ultimate tensile strength of 380.1 MPa, yield strength of 360.1 MPa, and elongation of 10.4%. The ignition point increases from 556 °C for the Ca-free alloy to 824 °C for the 1.8 wt.% Ca alloy, attributed to the formation of a dense CaO−MgO oxide layer. These findings demonstrate that calcium alloying offers a cost-effective, rare-earth-free pathway to simultaneously improve mechanical integrity and ignition resistance in magnesium alloys.