A novel process for improving fatigue properties of TIG welded AZ31B mg alloy joints by laser bionic treatment

Abstract

It is crucial to obtain better fatigue life for the safe application of materials, and nature provides a new idea for effectively improving fatigue property. A ‘soft-hard’ alternating structure imitated biological morphology was fabricated on the surface of welded joints by laser bionic treatment (LBT) for improving the fatigue property of TIG welded AZ31B Mg alloy joints. After LBT, the grains in the weld zone were refined with the average grain size about 5.55 μm and decreased by 76.1%, resulting in an increase of hardness of 12.0% to about 60.12 HV0.1, and formed a ‘soft-hard’ structure on the surface of welded joints. By adjusting the distribution angle of laser bionic stripe, the high cycle fatigue strength of welded joints was increased by 129.4% at most. The fracture morphology of welded joints was changed by LBT. The weld zone of bionic welded joints was deformed by twinning and slip, while the laser-treated zone was only deformed by slip. The mechanisms of strengthening fatigue properties were discussed based on the microstructure and structural characteristics from EBSD analyze.