Experimental Research on Laser Welding of AZ31B Magnesium Alloy Using Power-modulated Ring-mode Fiber Laser

doi:10.3901/JME.2025.02.151

Abstract

Abstract: Three common issues in magnesium alloy laser welding are poorly formed weld-seams, coarsen grains and deteriorated quality of joints. A novel process to weld magnesium alloys by laser deep melting is proposed, and it synergizes the effect of the circular spot of fiber laser and the sinusoidal modulation of power. The impact of power modulation parameters on surface formation, microstructure, and the mechanical properties of butt joints has been investigated thoroughly, and AZ31B is used as the welding materials in investigation. By comparing the welds from a circular spot laser with constant power, the investigation finds that the proposed process has improved surface collapse in weld seam significantly, the welds are formed uniformly when a circular spot laser with a central beam power modulation is applied. Moreover, a low fluctuation of the speed of molten metal on welded surface has produced more stable keyholes and fish-scale patterns on the welds uniformly. It is found that central beam power modulation also improves the microstructure of welds. By setting a modulation frequency appropriately, the zone with fine equiaxed crystals has been widened in the center of welds, and the zone with coarse crystals in the heat-affected zone has been reduced. However, when the modulation frequency is too high, the zone with equiaxed crystals is eliminated in the center of weld, and it forms numerous coarse crystals and some grains with internal deformation. When the amplitude and frequency of power modulation are as 500 W and 200 Hz, respectively, the tensile strength of joint reaches 233.41 MPa, and the corresponding elongation rate is 9.52%; these welding properties are approximately 82.3% and 76% of the base material, respectively. The failure modes are primary ductile fractures globally and secondary intergranular fractures in locally.

Key words: laser welding, AZ31B magnesium alloy, ring-mode laser beam, power modulation, microstructure and performance

CLC Number:

TG456

ZHANG Mingjun, LI Chenxi, ZOU Jianglin, CHENG Bo, ZHANG Jian, TONG Yonggang, HU Yongle, CHEN Genyu. Experimental Research on Laser Welding of AZ31B Magnesium Alloy Using Power-modulated Ring-mode Fiber Laser[J]. Journal of Mechanical Engineering, 2025, 61(2): 151-161.

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