Effect of ultrasonic impact treatment on surface microstructure and fatigue properties of 6082 aluminum alloy butt joint

Effect of ultrasonic impact treatment (UIT) on microstructure and fatigue properties of the aluminum alloy 6082 was studied at room temperature. The change of microstructure on the surface and the grain size after impact treatment was observed by metallographic microscope and transmission electron microscopy, respectively. The residual stress was measured by residual stress tester. The experimental results show that the UIT can lead to obvious plastic deformation layer in the treated surface, and nanocrystals were formed. Compressive residual stress of 50.4 MPa was maximum at the surface after the UIT. With an impact current of 1.0 A and impact time of 2 min, compared with untreated specimens, the fatigue strength of the 6082 aluminum alloy joint increases by about 11.18%. The fracture position for the treated specimen has been changed, the crack initiation is seen in the weld toe surface for the as-welded joint, and the crack initiation in the sub-surface for the treated specimen is comparable to the as-welded joint fatigue.