Effect of heat treatment on microstructure and mechanical properties of extruded ZM61 magnesium alloy

The effects of T5 and T6 heat treatments on the microstructure and mechanical properties of extruded Mg–6Zn–1M n alloy were investigated in the present study. The results showed that T5 and T6 treatments could markedly improve the strengths of extruded ZM61 alloy, and the precipitate strengthening effect of double aging was better than that of single aging. The precipitates formed in the T6 treatment were much finer and more dispersive than the ones in the T5 treatment, resulting in stronger precipitation strengthening effect. However, due to additional grain size refinement strengthening effect, the T5 treatment could improve ductility without sacrificing strength over the T6 treatment. Scanning electron microscopy observation and tensile test indicated that different cooling methods after extrusion, such as air cooling and water quenching, had no obvious influence on the microstructure and strengths of extruded and subsequent heat treated Mg–6Zn–1Mn alloys. In addition, the Mn element mainly existed as fine Mn phase particles, which were well dispersed in the matrix. Dispersed Mn particles could be found in rod-like precipitates, but not in the disc shaped precipitates.