Investigation on the joining process and strength of laser circle welding between Al5052 and CFRP dissimilar materials

Abstract

Laser welding is an effective approach to joining metal and composite. In the present research, laser circle welding was proposed to join the Al5052 sheet and PA6-CFRP as the first try. A process window was suggested according to the welding results and joint appearance. Single lap shear test was employed to evaluate the mechanical performance of welded joints under different welding conditions. The cross-section and fracture surface were subjected to multi-scale characterizations to subdivide the joining zone and understand the joining process. The result showed that 10 sets in 18 groups of welding parameters can achieve successful bonding. The welding results can be classified into four categories: non-connected, aging-failing, effective-joining and burn-through. The joining zone of laser circle welding was divided into three subregions. The adhesive zone (AZ) presented an interfacial fracture while the local failing passed through plastics basement in cohesive (CZ). The overheating of CFRP generated decomposed zone (DZ). The signal peak of O-C=O bond disappeared in the entire joining zone on CFRP sheet and the intensity of carbide was significant in DZ. The laser circle welded joint presented brittle and ductile fracture modes, which were related to the joining zone component. The joining strength can reach about 656 ± 22 N, 2135 ± 331 N and 3223 ± 257 N under one-circle, double-circle and three-circle scanning, respectively. Increased scanning numbers can decrease the required laser power and improve joining strength by extending heating time, while it also increased the risk of burn-through.