The effect of laser beam intensity distribution on weld characteristics in laser welded aluminum alloy (AA5052)

The distribution of laser beam intensity can play a key role in laser welding, since it is deeply related to the temperature gradient and cooling rate of the melt pool. In this study, aluminum alloy butt welding was conducted using a normal Gaussian beam and modulated beams with various intensity profiles, produced with a diffractive optical element (DOE). Their effect on the weld characteristics was investigated. Welding with the modulated beams generally required larger heat input for full penetration compared with the Gaussian beam welding (GBW) since laser energy was spread by the core and ring beam combination. This laser energy spreading reduced weld defects and produced a funnel-shaped weld cross-section in the modulated beam welding (MBW). Microstructure analyses found that the GBW and MBW had different grain growth behaviors based on the shape of the melt zone boundary. A straight melt zone boundary formed along the vertical direction induced columnar grain growth along the horizontal direction in the GBW. For the MBW, it grew along the diagonal direction, because the melt zone boundary had a slanted shape. The highest tensile strength (208.2 MPa, which corresponded to similar to 91% of the tensile strength of the base material) was obtained with the MBW, owing to reduced average grain size. It was found that the re-crystallization process induced by laser welding significantly increased the grain size of the original material.