Micromechanisms of edge cracking in rolled ZK60 magnesium alloy sheets under multi-coupling effects

The industrial application of ZK60 magnesium (Mg) alloy sheets is limited by edge cracking during the rolling process. This study systematically investigates the edge cracking behavior of the magnesium alloy sheets under different reduction ratios through multi-pass hot rolling experiments and finite element (FEM) simulation. Furthermore, by employing electron backscatter diffraction (EBSD), combined with in-grain misorientation axis (IGMA) analysis and twin analysis, the synergistic mechanism of slip and twinning on crack propagation is elucidated. The study found that no edge cracks were observed at a 30 % reduction rate, while higher reduction rates promoted the formation of 45° shear cracks. Both the length and number of cracks increased significantly with greater reduction. These observations align with the FEM-predicted stress distributions. Microstructural analysis reveals that damage accumulation and void coalescence are closely associated to crack initiation. At lower reduction ratios, crack propagation was dominated by the intergranular mode, primarily associated with the incoordination of grain boundary sliding. With the increase in reduction ratios, multiple slip systems are activated synergistically. The twin type at the crack tip transitions from compression twins and complex twins to being dominated by {10–12} tensile twins. Correspondingly, the crack propagation mode gradually evolves from an intergranular-dominated mode to a mixed intergranular-transgranular mode. This study provides a microstructural basis for subsequent investigations into the mechanisms of edge crack during Mg alloy rolling. • Reveals the evolution of crack propagation from intergranular to mixed modes with increasing reduction. • Identifies slip-system incompatibility at grain boundaries as the root cause of intergranular crack initiation. • Proposes the “minimum energy principle” to explain crack-path selection between brittle interfaces and plastic channels. • Establishes a multi-scale mechanism linking macroscopic stress, microscopic deformation, and crack evolution.