Influence of Er addition and extrusion temperature on the microstructure and mechanical properties of a Mg–Zn–Zr magnesium alloy

Abstract

Mg-1.5Zn-0.6Zr alloys with 0–4 wt.% Er addition were prepared by semi-continuous casting and extruded. The effects of Er addition and extrusion temperature on the microstructure evolution and mechanical properties were examined. The results showed that Er had a moderate grain refinement effect on the Mg-1.5Zn-0.6Zr alloy. The grain size was refined to ∼62 μm when adding 2 wt.% Er. Moreover, the addition of Er inhibited the formation of the divorced Mg–Zn binary eutectics and led to the formation of thermal stable Mg–Zn–Er intermetallics. The volume fraction of these intermetallic particles increased with increasing Er addition. Er was found to promote a higher degree of recrystallization and more homogenous microstructure when extruded at lower temperature of 350 °C. At higher extrusion temperature of 420 °C, Er effectively suppressed the grain growth; the Er-containing alloys demonstrated fine and uniform recrystallized grains of 4–6 μm in size. The comprehensive mechanical properties were greatly enhanced by the addition of Er. After extrusion at 420 °C, the 1 wt.% Er-containing alloy exhibited the best ultimate (305 MPa) and yield strength (285 MPa), with a large tensile elongation of 25%. The improved microstructure and mechanical properties could be ascribed to both the dissolved Er in the α-Mg solid solution and the thermal stable Mg–Zn–Er intermetallics.