Microstructure and mechanical properties of ZK60-Er magnesium alloys

The effects of Er addition on the microstructure and mechanical properties of ZK60 alloy were investigated. Cast ZK60-Er (0, 0.5, 1, 2 and 4 wt%) ingots homogenized at 350 °C were extruded at 400 °C. It was found that Er primarily existed in the form of Mg-Zn-Er intermetallic particles instead of Er-containing α-Mg solid solution. Due to the formation of Mg-Zn-Er particles, the dissolution of Zn solutes in homogenized billets decreased with increasing Er modification. Typical fiber textures along with dynamically precipitated spherical Mg-Zn compounds were developed during the extrusion process. Mg-Zn precipitates gradually decreased with the increasing Er level. Er addition slightly decreased the elongation and scarcely increased the tensile strength of the extruded bars. The extruded alloys with different Er contents shared similar microstructural evolutions in the subsequent heat treatment. No Er-bearing precipitates were found in the heat treated bars. Mechanical strengths decreased but the plasticity increased by increasing the solutionization time from 1.5 h to 12 h at 400 °C. Upon further aging at 200 °C for 10 h, there was no significant change in the optical microstructure while Mg-Zn compounds statically precipitated. The plasticity could be compensated by the decrease of defects caused by the static precipitation of Mg-Zn compounds.