Crack propagation path deflection induced by α-Mg / LPSO interface and its effect on the fracture toughness of cast Mg-RE-Zn alloys

• Heat treatment regulates the morphology of LPSO to achieve different α-Mg / LPSO interfaces. • The α-Mg / LPSO interface affects crack initiation and propagation. • To improve toughness, it is necessary to control the size and distribution of blocky LPSO while avoiding lamellar LPSO. The poor fracture toughness limits the widespread application of high-strength cast Mg-Re-Zn alloys. Regulating the alloy microstructure, with phases such as α-Mg, blocky LPSO (long-period stacking order), and lamellar LPSO, offers various possibilities to enhance ductility by casting and heat treatment. This study categorizes different interface types concerning crack initiation, propagation, and ultimate fracture toughness. It distinctly presents the results of interface modulation related to alloy composition and heat treatment, elucidating the influence on crack initiation and propagation paths. Consequently, it proposes structural configurations rule and relevant heat treatment processes that can optimize and improve alloy fracture toughness. Blocky LPSO should have appropriate dispersion and size while avoiding lamellar LPSO.