Porosity formation and its effect on the properties of hybrid laser welded Al alloy joints

Laser-arc welding is increasingly applied for joining aluminum alloys. A critical issue in laser-arc welding Al alloys is the existence of pores which can significantly influence the in-service properties of the welded joints. How to control the porosity, therefore, is of importance in both academic and industrial worlds. In this paper, effects of welding parameters on the degree of porosity in welded joints were investigated. The distribution and size of pores were characterized by X-ray and synchrotron radiation X-ray detection methodology. It was found that the porosity was successfully controlled by adjusting welding parameters. Specifically, the macropores were reduced dramatically by increasing arc currents and decreasing laser powers. Macropore-free joints were obtained with some welding parameters. The mechanism of controlling macropores was presented. Moreover, the results from mechanical testing showed that the pores did not obviously influence the mechanical properties for low percentage of porosity in the range of near 0 to 4%, but decreased the fatigue strength of the joints. EBSD results illustrated that the grain size of the fusion zone was about 74 ± 58 μm, and no obvious texture was found within the fusion zone.