Study of fatigue crack growth characteristics of TIG welded AZ31B magnesium alloy joint based on laser bionic treatment.

It is crucial to obtain better fatigue property for the safe application of materials, while nature provides new structural design ideas for effectively improving fatigue property. In this study, a "soft‐hard" alternating bionic structure was fabricated on the surface of TIG welded AZ31B Mg alloy joints by laser bionic treatment (LBT). Microstructure of welded joints was tailored by LBT, resulting in fine equiaxed grains with random orientations and increased microhardness. The fatigue crack growth threshold of the welded joints with bionic structure is increased by more than 40%, and crack growth rate was lower. LBT could significantly affect crack growth behavior and presented obvious crack deflection, resulting in a rougher fracture surface and more second cracks and branches. LBT significantly improved the fatigue crack growth resistance, inducing a series of strengthening mechanisms. The present work opens a new alternative to improve the fatigue properties of welded joints. Highlights: "Soft‐hard" alternating structure was formed in joints by laser bionic treatment (LBT).The refined grains coupled with coarser grains provide the ideal microstructure.Fatigue crack growth resistance of welded joints was improved significantly by LBT.Strengthening mechanisms induced by LBT were discussed. [ABSTRACT FROM AUTHOR]