Effects of aluminum content and strain rate on strain hardening behavior of cast magnesium alloys during compression

The aim of this study was to identify the effects of aluminum content and strain rate on the compressive strain hardening behavior of AZ31, AZ61 and AZ91D cast magnesium alloys. The yield strength (YS) and ultimate compressive strength (UCS) of the alloys increased but the strain to failure decreased with increasing aluminum content, due to the presence of an increasing number of β-Mg17Al12 particles. The YS increased slightly with increasing strain rate, while the strain-rate dependence of the UCS and the strain to failure was basically absent, leading to a decreasing hardening capacity. The strain hardening exponent and strength coefficient evaluated via four equations of Ludwik, Hollomon, Swift, and Afrin et al. showed a similar increase with increasing strain rate in the AZ31 alloy, but were nearly independent of strain rate in the AZ61 and AZ91D alloys. The strength coefficient increased with increasing aluminum content based on all the four equations. The three alloys exhibited stage III hardening followed by stage IV hardening. AZ31 alloy had the longest stage IV hardening and the highest strain to failure, followed by AZ61 and AZ91D alloys.