Microstructure and porosity characteristics of 5A06 aluminum alloy joints using laser-MIG hybrid welding

5A06 aluminum alloy plates with thickness of 6.9mm are welded by KUKA Robot with a fiber laser of IPG YLS-6000. The laser-metal inert gas (MIG) hybrid welding method is adopted to provide high overall productivity in this paper. To investigate the joints microstructure and porosity distribution, optical microscope observation, scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) detection are conducted. The pores of laser-MIG hybrid welding joint are mainly metallurgical pores which are caused by the dissolved gases and evaporation of Mg element. This metallurgical pores are densely populated in the upper area of weld joint. Besides, the micro-hardness along the weld center line and perpendicular to the weld center line are separately analyzed. The joint softening can be evidently observed near heat affected zone (HAZ) and in weld bead (WB), where the grain enlargement or pores problem exist. It claims that the formation of pores has a much greater influence on the joint softening than grain enlargement. In order to get a low-porosity weld joint, as well as owning a high level of micro-hardness, the porosity and micro-hardness in different laser-MIG hybrid weld joints are analyzed comprehensively. The welding speed of 3m/min is more suitable to be applied in laser-MIG hybrid welding for the 6.9mm 5A06 aluminum alloy.