Minimizing defects and controlling the morphology of laser welded aluminum alloys using power modulation-based laser beam oscillation

Abstract

Due to sensitivity to heat, laser welding of aluminum alloys is always accompanied by serious defects such as porosity and cracks, which restricts their wide application for structures of lightweight applications. Beam oscillating welding can potentially eliminate these defects to a large extent but with shortcoming of low heat utilization rate. For better solution, a Full Domain Power Modulation (FDPM) system was promoted to conduct bead-on-plate welding tests of 6061 aluminum alloys using circular oscillation. The impact of three welding modes (traditional Laser Welding, Constant Power (CP), Gradient Power (GP)) and oscillation frequency on the weld morphology, porosity, and microstructure was examined by Optical Microscopy (OM), Electron backscatter diffraction patterns (EBSD) and industrial Computed Tomography (CT). The results demonstrated that at the same frequency, the weld depth-to-width ratio in GP mode exceeded the CP mode. The strong stirring effect promoted the pores to escape and increased the heterogeneous nucleated particles of the molten pool, which yielded the lowest weld porosity and the largest equiaxed crystal ratio in GP mode. The mechanism of porosity removal and grain refinement was determined based on the calculated energy distribution. This study provides a brand new approach for porosity inhibition and microstructure optimization of laser-welded aluminum alloys.