Effects of reduced extrusion temperature on microstructure and mechanical properties of Mg–6Zn–0.5Zr alloy

Improving the strength of the commercial ZK60 alloys plays a key role in promoting their wide applications. In this work, a ZK60 alloy was prepared by conventional direct extrusion at an obviously reduced temperature of 180 °C. Compared with ZK60 alloys directly extruded at high temperatures (>300 °C), the studied alloy has finer dynamic recrystallized (DRXed) grains with the average size of ∼1.7 μm, stronger typical fiber texture and more profuse lath-like sub-grains. In addition, the ultra-low extrusion temperature increased dynamic precipitates (rod-like Mg4Zn7 and MgZn2) in DRXed grains. After aging, a great many of nanosized precipitates formed in both DRXed grains and non-recrystallized grains, and relatively coarse MgZn2 particles precipitated on sub-grain boundaries. As a result, the aged ZK60 alloy exhibit significantly high ultimate compressive strength of ∼675 MPa on the basis of high yield strength of ∼310 MPa, indicating a significant strain hardening capability. Meanwhile, it has excellent strength-ductility balance and a weakened tension-compression yield strength asymmetry under owning a high TYS in order of ∼400 MPa.