Strain Hardening and Strain-Rate Sensitivity of an Extruded Magnesium Alloy

The strain-hardening behavior and strain-rate sensitivity of an extruded AZ31B magnesium alloy were determined at different strain rates between 10⁻² and 10⁻⁵ s⁻¹ in relation to the thickness of specimens (2.5 and 4.5 mm). Both the common approach and Lindholm’s approach were used to evaluate the strain-rate sensitivity. The yield strength (YS) and the ultimate tensile strength (UTS) increased, the ductility decreased, and the brittle fracture characteristics increased with increasing strain rate. The thinner specimens exhibited a slightly higher UTS, lower ductility, higher strain-hardening exponent, and strain-hardening rate due to smaller grain sizes. The stage III strain-hardening rate linearly decreased with increasing true stress, but increased with increasing strain rate. In comparison to the common approach, the Lindholm’s approach was observed to be more sensitive in characterizing the strain-rate sensitivity due to larger values obtained. The thinner specimens also exhibited higher strain-rate sensitivity. As the true strain increased, the strain-rate sensitivity decreased.