Effect of pulse overlap rate on the microstructure and mechanical properties of laser welds of thin AZ31 magnesium alloy

Abstract

In order to improve the quality of pulse laser welding on magnesium alloy, the effect of pulse overlap rate on the microstructure and mechanical properties of the welds is studied. A Nd:YAG pulsed laser welding machine is used to carry the butt welding experiments on AZ31 magnesium alloy (1 mm), and the pulse overlap rate (10%, 30%, 50%, 70%, 90%) is varied by adjusting the welding velocity. The experimental results show that with the increases of pulse overlap rate, the sensitivity of the solidification cracks and pores decreases. The grain size of the columnar grains at the fusion boundary (FB) and the equiaxed grains in the center of the welds increases and then decreases and reach the maximum value of 114.72 ± 3.06 μm and 74.08 ± 5.87 μm, respectively, when the overlap rate is 70%. The percentage of the ductile fracture in the fracture of tensile specimens is proportional to the pulse overlap rate. With the increases of the pulse overlap rate, the tensile strength and maximum force show a trend of decreasing first and then increasing, and both reach the maximum value of 94.583 MPa and 1.135 kN when the overlap rate is 90%. Besides, the microhardnesses of the welds decrease first and then increase, which the maximum value is 86 HV0.2. In summary, the welds with better surface morphology can be obtained at the pulse overlap rate of 70%, while the mechanical properties of the welds are better when the overlap rate is 90%.