Effect of tensile strain rates on flow stress for extruded AZ31 and AZ61 magnesium alloys

Abstract

Aluminium-Zinc (AZ) is a popular series of magnesium alloy and is used in automobile components and structures. In this regard, the AZ series is subject to high velocity and impact loads during accidents. Thus, it is essential that the effect of tensile strain rates i.e., low and intermediate strain rates, on flow stress of extruded AZ31 and AZ61 magnesium alloys is investigated. In this study, tensile test under low strain rates were fixed at 1×10^-4 , 1×10^-3 , 1×10^-2 and 1×10^-1 s^-1 , while tensile tests under intermediate strain rates were fixed at 100, 200, 400 and 600 s^-1. The tensile test specimens were prepared with a gage length and diameter of 10 mm and 3 mm, respectively. Flow stress was determined by averaging the values of yield stress and tensile strength of the alloy. The results showed that the flow stresses of both extruded magnesium alloys were strain rate dependent. This is believed to be due to the increasing dislocation density in the materials. Thus, the resistance to deformation increased with an increasing volume of dislocation density for extruded AZ31 and AZ61 alloys. Moreover, the flow stresses of both alloys were strain rate dependent; the activation of critical resolved shear stress (CRSS) of non-basal slip systems for magnesium alloys significantly influenced the deformation mechanism of the materials. Additionally, flow stresses of both magnesium alloys increased at increasing strain rate due to the large numbers of twinning in alloys. Hence, tensile strain rates significantly affect the flow stress and failure mechanism of magnesium alloys.