Interfacial microstructure and mechanical properties of laser-welded 6061Al/AISI304 dissimilar lap joints via beam oscillation

Oscillating laser welding of 2-mm-thick 6061-T6 aluminum alloy and AISI304 steel in overlap configuration was performed under various oscillation amplitudes of 0, 3, and 5 mm. The experimental results indicated that the welding window of Al/steel dissimilar joints was improved with increasing oscillation amplitudes. The beam oscillation broadened weld width and interfacial bonding width while reducing weld depth. In the joint produced under 0-mm oscillation, a multi intermetallic compound (IMC) layer formed with a thickness of about 90 μm. In the joint produced under 3-mm oscillation, the IMC layer with the compositions of η-Fe2Al5+block-shaped θ-Fe4Al13) was obtained and its corresponding thickness reduced to 20 μm. When the oscillation amplitude further increased to 5 mm, only a η-Fe2Al5+little θ-Fe4Al13 layer with a thickness of 5 μm generated. Simulation results for the temperature history indicated that an oscillating laser beam would disperse laser energy, restraining the steel penetrating. Besides, dispersed heat energy depressed the melting of lower aluminum sheets and interfacial element diffusion. Thus, the formation of IMCs was suppressed. The limited IMCs and increased bonding width led to an improvement in the tensile–shear properties. The maximum fracture load of the joint under 5-mm oscillation was 185 N/mm, which was twice higher than that of joints welded without beam oscillation. Less Al atoms dissolved into the fusion zone under beam oscillation, resulting in lower microhardness and better toughness. Fracture locations changed from the fusion zone to the interface due to weakened steel penetration and improved toughness.