Structural and mechanical characteristics of Mg-4Zn and Mg-4Zn-0.4Ca alloys after different thermal and mechanical processing routes

This work studied as-cast, T4 heat-treated and ECAPed Mg-4Zn and Mg-4Zn-0.4Ca alloys using light, scanning and transmission electron microscopy, as well as X-ray diffraction, differential scanning calorimetry and mechanical testing. The as-cast alloys consisted of α-Mg dendrites, MgZn and Ca2Mg6Zn3 phases. The T4 heat treatment led to the dissolution of the MgZn phase, but the Ca2Mg6Zn3 phase was not significantly affected by this treatment. The process of ECAP resulted in significant structural refinement, fragmentation and the precipitation of intermetallic phases. Hardness, compressive and tensile yield strengths were significantly increased by the ECAP process. Moreover, the addition of Ca had a positive effect on the mechanical properties of the magnesium alloy. The maximum ultimate tensile strength of the ECAPed Mg-4Zn-0.4Ca alloy was 250 MPa. Mechanical tests at elevated temperatures and after heat treatments revealed that the ternary Mg-4Zn-0.4Ca alloy exhibited better thermal stability than the binary Mg-4Zn alloy. Differences in the mechanical behaviors of both alloys were discussed in relation to structural variations.