Influence of Stress Triaxiality on Tensile Properties at Cryogenic Temperature in Mg-3Al-1Zn Alloy

This paper experimentally investigates the influence of stress triaxiality on cryogenic tensile properties and fracture behavior in AZ31 magnesium alloy. Tensile test was performed with notched round bar specimen with static loading speed at two tested temperatures: room temperature and 83 K. A range of stress triaxiality was adopted 0.3 to 1.4 in this study: dimension in smooth bar specimen corresponds to stress triaxial value of 0.3, and that in notched round bar specimen with notch-root-radius of R =1 corresponds to the value of 1.4. Critical plastic strain (i.e., plastic strain at breaking point) based on Bridgman’s equation was calculated. As a result, it was found that a tendency towards large decrease in cryogenic ductility: the decrease of ductility of 13 % for low stress triaxial value of 0.3, and 24 % for high value of 1.4 compared to RT. Below figure shows relationship between critical void growth rate by Rice and Tracy model and stress triaxiality, and indicates also macrophotograph of the fracture behavior at testing temperatures of RT and 83 K. Low critical void growth rate at 83 K is confirmed and unstable rapid fracture manner with a distinct fracture point is observed under cryogenic temperature.