Planetary laser welding system induced equiaxed and refined grains in 2A12 aluminum alloy weldments

In this paper, a novel welding technology realized by planetary system laser was proposed. The crystal orientation and growth features in the fusion zones were studied and compared to the result of single laser welding. The single laser welding produced conventional columnar and equiaxed growth of alpha-Al dendrites in the fusion zone. These two regions both possessed newly nucleated tiny grains and overgrown huge grains. The planetary system laser welding enhanced the free nucleation procedure and promoted the columnar to equiaxed transformation. Compared to a single laser, the average grain misorientation was increased while the aspect ratio and grain size were decreased. Also, the entire orientation distribution exhibited a considerably dispersed fashion. In summary, the planetary system laser welding presented stirring force and disordered heat diffusion during solidification process. The former directly broke up the protuberant tips of trunks and multiplied the number of existing dendrites. The latter reduced the high throughput heat diffusion and produced a relatively lowtemperature gradient, thus elevating the supercooling and radial overgrowth of dendrites.