Hybrid laser welding of dissimilar aluminum alloys: welding processing, microstructure, properties and modelling

Hybrid laser-arc welding of aluminum alloys has been receiving more and more attention in academic and industrial communities. The outstanding mechanical and fatigue properties of laser-arc welded joints with similar Al alloys have been demonstrated in literatures. Very few studies, however, reported the microstructures and properties of laser-arc welded joints with dissimilar Al alloys, while they are increasingly applied in modern engineering structures. Here, we study laser-arc welding of two dissimilar Al alloys, AA5083 and AA7N01. Their weldability, microstructures and properties are particularly investigated. Results show that sound welded joints of dissimilar Al alloys can be obtained via adjusting welding parameters. Microstructural characterization via SEM, EBSD and TEM reveals that microstructure in the fusion zone (FZ) is featured by large precipitates, low dislocation density, and coarsened grains with an average size of 66 +/- 57 mu m. The tensile strength of FZ of coarsened microstructure is degenerated to 230 MPa, which is the lowest among the three zones. The fatigue strength of the joints is 110 MPa, about 40% of their tensile strength. Pores and inclusions are the main sources for the deterioration of fatigue strength, as evidenced from SEM observations. In addition, a strength model is successfully built and utilized to simulate the yield strength, strain rate hardening and work hardening behavior of fusion zone.