Mechanism of high-strength and ductility of Mg-RE alloy fabricated by low-temperature extrusion and aging treatment

Through studying the effect of initial microstructure on the precipitation behavior, microstructure evolution and mechanical properties of Mg-6Gd-4Y-0.5Zn-0.5Zr alloy, an effective way to fabricate high-strength and ductile Mg-RE alloy was proposed by low-temperature extrusion and aging treatment, where the contribution of various strengthening mechanisms was quantitatively analyzed. The results indicate that the difference of initial microstructures had no evident influence on the precipitation behavior of the Mg-RE alloy. Static recrystallization took place in the alloy with low-temperature extrusion of 300 °C during aging treatment at 200 °C due to relatively higher dislocation density in the deformed grains, which offset the reduction of elongation caused by aging treatment and resulted in the good combination of strength and ductility. In the high-strength Mg-RE alloy, grain boundary strengthening, solid solution strengthening, and precipitation strengthening are the main strengthening mechanisms. As shearable β’ particles by basal slip existed in the Mg matrix, precipitate shear strengthening other than Orawan bypassing strengthening should be utilized in predicting the precipitating strengthening behavior of Mg-RE alloy. [Display omitted] •An Mg alloy with excellent balance of high strength and ductility is fabricated.•The strengthening mechanism of the high-strength Mg alloy is quantitatively analyzed.•Inducing static recrystallization during aging treatment can optimize the ductility of Mg alloy.•Precipitation shearing strengthening is the accurate strengthening mechanism of β′ phase.