Effect of energy ration on residual stresses in laser-MIG hybrid welding of aluminum alloys

Objective The purpose was to investigate residual stress distribution law and mechanism of laser-MIG hybrid welding of 7075 aluminum alloy under different energy ratios. Methods Welding heat cycle at different positions of workpiece was measured in the welding process, residual stress distribution of laser-MIG hybrid welded joints was measured by X-ray diffractometer after welding, and change rule of residual stress of welded joints under different energy ratios was analyzed. Results The results showed that when the total heat input was unchanged, with the increase of laser power and the decrease of MIG power, welding penetration ability was enhanced, penetration of weld gradually increased, and width of weld gradually decreased. When energy ratio coefficient was too large, quality of weld formation decreased. Residual stress showed overall bimodal distribution in the direction perpendicular to weld, tensile stress presented near the weld area, and compressive stress presented in the base material area. In the direction parallel to weld, residual stress manifested a “compression-pull-pressure” trend. Conclusion Because laser energy was more concentrated, peak temperature of heat-affected zone showed an obvious upward trend with the increase of energy ratio coefficient. Therefore, with the increase of laser power ratio, a higher temperature gradient was formed, which led to the increase of residual stress in the concentrated heating area. At the same time, due to the reduction of MIG power ratio, residual stresses in the weld and the area outside heat affected zone showed a significant decreasing trend.