Study on the creep fracture mechanism of the Mg-Al-Zn extrusion plate during creep forming

Abstract

Both the creep resistance and creep forming of the light-weight Mg alloys involve the interaction between dislocations and second-phase particles. However, current researches have predominantly focused on the steady creep stage while neglecting the analysis of creep fracture behavior. In this study, the creep mechanisms and creep fracture behaviors of the Mg-Al-Zn extruded plate are analyzed, via advanced characterization techniques such as scanning electron microscopy and transmission electron microscopy. The results indicate that basal <a> slip and cross-slip are the dominant creep mechanisms under the creep conditions of 423 ∼ 463 K and 40 ∼ 100 MPa. Furthermore, <a> dislocations not only induce the transition of the dominant texture component from {0001} < 10$\overline{\text{1}}$0 > to {11$\overline{\text{2}}$0}<0001> component, but also contribute to the formation of dislocation networks and the dynamic precipitation of β-Mg₁₇Al₁₂ phase near grain boundaries. Under the combined action of dislocation activation, dislocation networks and β-Mg₁₇Al₁₂ phase, voids and cracks occur near these second phase and are stretched out along the creep direction, and lead to the creep failure, accelerating a theoretical foundation for Mg alloys with creep resistance or creep forming.