Double-Sided Oscillating Laser Welding on Thick AZ31B Magnesium Alloy Plates

To improve the formation and quality of welds in joining two thick plates with AZ31B magnesium alloy, we proposed the double-sided oscillating welding technique to weld AZ31B plates with a thickness of 5 mm, and we validated the performance of the proposed technique experimentally by investigating the weld formations, microstructures, and mechanical properties of the welds on the joined specimens using metallographic microscopy, scanning electron microscopy, and tensile testing machine. The investigation showed that the proposed technique outperformed traditional single-sided welding in sense that double-sided oscillating welding stabilized the molten pool, achieved full penetration in the weld formation, prevented collapsed, and suppressed pores in the weld. At the overlap of two sequential welds, the remelting effect coarsened equiaxed grains. When the oscillation laser frequency was set to 100 Hz and the amplitude was 1.0 mm, the resulted weld had a tensile strength of 233 MPa and an elongation of 9.6%, these values were equivalent to 82% and 76% of the properties of the base materials, respectively, with a fatigue strain range of 0.142-0.269 mm. Under the same cyclic load, a comparison of the welds by single- and double-sided laser welding showed that the latter had smaller strains and improved the mechanical properties by over 130%. In the tensile test of the weld by the proposed method, the fracture of the specimen was characterized predominantly by ductile fracture together with localized cleavages.