Effect of Strain Rate on Tensile Strength and Work Hardening for Al–Zn Magnesium Alloys

Abstract

The effect of strain rate on mechanical behavior of Al–Zn magnesium alloys was investigated at room temperature under tensile loading with a wide range of strain rate. The quasi-static tensile test was performed in four different strain rates to obtain their effect on tensile properties, work hardening rate, strain hardening exponent, and strength coefficient using a round shape tensile specimen. Two types of Al–Zn magnesium alloys were used in this study i.e., AZ31 and AZ61 magnesium alloys. The yield stress and tensile strength of AZ31 were found to be the strain rate dependent but not so clear for AZ61. The elongations of AZ31 were approximately 15 % for all strain rate levels. The elongation for AZ31 was slightly decreased with increasing strain rate, while that for AZ61 was significantly decreased. For all strain rate levels, the work hardening rate of AZ61 was higher compared to that of AZ31. The strain hardening exponent was decreased with increasing strain rate. In contrast, the strength coefficient was increased with increasing strain rate for both alloys. The change in the fracture mode as observed from the fracture surface implies that the fracture mechanisms in AZ31 change as the strain rate increases. Mechanical properties of AZ61 and AZ31 in this study were relied to the grain size, presence of precipitate, twinning and alloying addition. While, the strain rate dependency of AZ31 and AZ61 tensile strength might be due to the critical resolved shear stress (CRSS) of slip systems.