In-depth characterization of an aluminum alloy welded by a dual-mode fiber laser

Abstract

The power distribution of laser beam is an important parameter in laser welding in that it is closely related to the state of melt pool. In this study, a dual-mode fiber laser providing various beam power distributions by individual adjustments of the center and ring power was used for the butt-welding of an aluminum alloy, and the in-depth characterization of the welds produced by these power distributions was carried out. The ratio of the top to bottom bead width increased with an increase in the heat input (or ring power) because the ring beam only participated in the melting of the upper part of the workpiece. Voids were mostly not produced when ring power lower than the center power was used at a relatively high welding speed, and smooth bead surface was obtained at relatively high ring powers due to the gentle distribution of the temperature across the melt pool. It was found that the weld zone (WZ) consists of many columnar and few equiaxed grains. The average grain size of the WZ tended to increase with the ring power due to increased heat input and resultant low cooling rate. The mechanical strength of the WZ decreased with an increase in the ring power due to decreased grain size. However, this trend was not clearly observed when relatively low welding speed was used. It was observed that the fracture surface of weld joints was the typical ductile type.