Evolution of tension and compression asymmetry of extruded Mg-Al-Sn-Zn alloy with respect to forming temperatures

Substantial strength of as-extruded and as-forged ATZ842 alloys is attributed to precipitation strengthening due to the presence of fine Mg₂Sn and Mg₁₇Al₁₂ particles in the alloys. Because Mg alloys inevitably undergo dynamic recrystallization during the warm forging that is required for their net-shape processing, it is important to examine microstructural evolution in as-forged samples. The appropriate forging temperature was found to range from 250 to 300 °C; average grain size started to increase at temperatures over 350 °C due to abnormal grain growth and a reduction in the fraction of second-phase particles. The ATZ842 alloy showed mechanical properties superior to those of the AZ80 alloy, including yield and ultimate strengths in both tensile and compressive deformations. Remarkably, the tension and compression asymmetry in plastic flow of ATZ842 forged at 250 °C was characterized by a yield ratio of about 1.02, compared to the yield ratio of 0.88 for the AZ80 alloy.