Effect of laser bionic treatment on fatigue crack growth behavior of TIG welded AZ31B magnesium alloy joint.

• Grains of weld joint has refined by laser bionic treatment (LBT). • Fatigue behavior was correlated with 'soft-hard' alternating structure formed by LBT. • Roles of LBT in fatigue resistance improvement were discussed. In this study, laser bionic treatment (LBT) was utilized to improve the fatigue crack growth behavior (FCGB) of AZ31B magnesium alloy welded joints. After LBT, fine equiaxed grains with random orientations were achieved on welded joints. Meanwhile, gradient structure and surface strengthening layer with 'soft-hard' alternating structure were achieved on welded joints, and fatigue crack growth threshold was significantly increased, and fatigue crack growth rate was significantly decreased. LBT results in changes of FCGB and fracture mode, and can affect all stages of crack growth. In addition, the mechanism of strengthening fatigue was analyzed based on microstructure, fracture and structural characteristics. [ABSTRACT FROM AUTHOR]