Abstract: The present study investigates the enhancement of fracture toughness in Mg-RE-Zn alloys through a dual strategy: control of crystallographic texture and tailored distribution of long-period stacking ordered (LPSO) phase. Alloys with identical texture types but varying intensities and LPSO morphologies were fabricated via thermomechanical processing. Apparent fracture toughness was evaluated through three-point bending tests, with crack propagation aligned parallel to the basal plane - a direction known for poor fracture resistance in textured magnesium (Mg) alloys. Crystallographic parameters, including twist angle φ, tilt angle θ, misorientation angle α, and geometrical compatibility factor mʼ, were extracted from EBSD data to analyze their roles in crack deflection and propagation. Results revealed that the strip-shaped LPSO phase significantly promotes crack path deflection and secondary crack nucleation, whereas the blocky LPSO phase was less effective. Moreover, twist angle φ showed a strong linear correlation with fracture toughness when LPSO volume fraction remained below 8 % and grain size exceeded 20 µm. A predictive model based on twist angle φ and mʼ was proposed to estimate the fracture resistance of textured Mg alloys. This work offers critical insights into microstructural design principles for enhancing the toughness of lightweight structural materials.

Key words: Mg-RE-Zn alloy, Fracture toughness, Crack propagation, Microstructure, Texture