Effects of ultrasonic peening treatment on surface quality of CMT-welds of Al alloys

The porosity number and porosity area percentage of weld beads close to the weld surface reduce after ultrasonic peening treatment. The grains are refined significantly in severe deformation layer and transition layer. The refined grain size is approximately 200 nm on the surface of weld bead after ultrasonic peening treatment. The loads on severe deformation layer and transition layer are larger than those on weld beads without ultrasonic peening treatment with the same indentation displacement in nano-indentation tests. After ultrasonic peening treatment, the elastic modulus of the weld bead surface increases slightly due to the decrease of porosity fraction. The hardness values of severe deformation layer and transition layer increase, which leads to the enhancement of wear resistance of welded joints.