Enhancement of Mechanical Properties and Ignition Resistance of Mg-6zn-0.6zr Alloy Through Co-Addition of Ca and Y

Abstract

Based on the ZK60 (Mg-6Zn-0.6Zr, wt.%) alloy, this study designed two new ignition-resistant magnesium alloys, ZKX602 (Mg-6Zn-0.6Zr-1.6Ca, wt.%) and ZKXW6001 (Mg-6Zn-0.6Zr-0.6Ca-1.0Y, wt.%), and investigated the effects of a single addition of Ca and co-addition of Ca/Y at equal mass percentages on the microstructure, mechanical properties, and ignition resistance. Both as-cast alloys exhibited dendritic structures with continuous mesh-like second phase. The ZKX602 alloy contained Ca2Mg6Zn3 phase, while the ZKXW6001 alloy had both Ca2Mg6Zn3 and W-phase, with finer phase sizes. After homogenization, a few Ca2Mg6Zn3 phases dissolved in both alloys, while the W-phase in ZKXW6001 alloy was completely retained. After extrusion, both alloys exhibited a bimodal grain structure, with the retained phase fragmented into granular and banded morphologies, and MgZn nanoparticles dynamically precipitated in the matrix. The ZKXW6001 alloy showed superior mechanical properties, with ultimate tensile strength of 408.3 MPa, yield strength of 383.8 MPa, and elongation of 11.3%, due to its fine grain size, uniformly distributed phases, strong texture, and high-density residual dislocations. Additionally, the ignition point of the ZKXW6001 alloy reached 1056 °C due to a denser, thicker Y2O3-CaO-MgO-ZrO2 composite oxide layer. This finding emphasized the effectiveness of co-addition strategies in synergistically enhancing the mechanical properties and ignition resistance of magnesium alloys.

Keywords: Mg-Zn-Zr-Ca-Y alloy, Mechanical properties, Ignition resistance, Oxide layer