Effect of preheating temperature on the defects in pulsed laser welding of sheet AZ31 magnesium alloy

To suppress the welding defects of thin sheet magnesium alloy by pulsed laser welding, AC-300 W pulsed laser welder is used to weld 1 mm magnesium alloy at different preheating temperatures, and the effect of preheating temperature on solidification cracks, pore and undercut are studied. Preheating temperature is set at 25 ℃, 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300 ℃ and 350 ℃. Results show that preheating increases the peak temperature (1494.14 ℃ to 1785.86 ℃) and reduces the cooling rate (14489.33 ℃/s to 14282.11 ℃/s) of the molten pool, thereby reducing welding defect sensitivity. When preheated at 200 ℃, the solidification cracks and pores disappear, and the undercut depth reaches the minimum value of 0.04 mm.