Edge cracking mechanisms in extruded AZ31 alloy thin-walled components considering friction effects

High-performance magnesium alloy thin-walled components are highly desirable for the lightweighting of next-generation advanced weaponry and equipment. During the hot forming of these components, interfacial friction induces the evolutionary reconstruction of surface micro-morphology and microstructural gradients, which subsequently triggers surface crack initiation. In this study, the edge cracking behavior of Mg alloy thin-walled components under varying friction conditions and deformation amount is systematically investigated through backward extrusion experiments coupled with finite element method (FEM) simulations. The results indicate that with increasing deformation, the stress state of the components transitions from pure compression to tension or a complex tension–compression state. By combining electron backscatter diffraction, in-grain misorientation axis analysis and two-beam diffraction, the synergistic mechanisms between grain size and dislocation slip during crack propagation are elucidated. Under lubricated conditions, plastic deformation is primarily accommodated by deformation twinning. Conversely, under unlubricated conditions, crack initiation is intimately associated with incompatible grain boundary sliding. At low deformation amount, crack propagation is predominantly twin-induced, whereas multiple slip systems are synergistically activated at higher deformation amount. Ultimately, this work establishes a fundamental framework for understanding the cracking mechanisms in Mg alloy thin-walled components.