Laser-arc hybrid welding of AZ31B magnesium alloy by newly-designed beam oscillating pattern

To solve the uneven weld formation caused by the lower internal energy distribution of laser in circular beam oscillation, an inscribed double-circle oscillation was proposed for the laser-arc hybrid welding of magnesium alloy. Compared with the circular oscillation at frequency of 250 Hz, the inscribed double-circle oscillation not only improved the uniformity of laser energy distribution by 1.9 times, but also increased the stirring intensity of laser keyhole on the molten pool by 25 %. The difference between the upper wide flow and lower narrow flow existing in circular oscillating hybrid welding pool was reduced by promoting turbulent flows at their boundary via inscribed double-circle oscillation. Due to these improvements, the rough surface formation and uneven penetration depth existed in circular oscillating hybrid weld was suppressed, and the fracture area during tensile tests transferred from the weld center to base metal. The corresponding ultimate tensile strength and elongation of the magnesium alloy weld reached 241 MPa and 9.7 %, showing an increase up to 11 % and 115 % respectively.