Influence of pre-deformation on age-hardening response and mechanical properties of extruded Mg-6%Zn-1%Mn alloy

The effect of cold plastic deformation between solution treatment and artificial aging on the age-hardening response and mechanical properties of alloy was investigated by micro-hardness test, tensile test, optical microscopy (OM) and TEM observation. After solution treatment at 420 °C for 1 h, three kinds of pre-deformation strains, i.e. 0, 5% and 10%, were applied to extruded ZM61 bars. Age-hardening curves show that pre-deformation can significantly accelerate the precipitation kinetics and increase peak-hardness value; however, as pre-deformation strain rises from 5% to 10%, there is no gain in peak hardness value. The room temperature (RT) tensile properties demonstrate that increasing the pre-deformation degree can enhance the yield strength (YS) and ultimate tensile strength (UTS) but moderately reduce elongation (EL); furthermore, the enhancement of YS is larger than that of UTS. No twin can be observed in 5% pre-deformed microstructure; however, a large number of twins are activated after 10% pre-deformation. The peak-aged TEM microstructure shows that pre-deformation can increase the number density of rod-shaped β1′ precipitates which play a key role in strengthening ZM61 alloy.