Bonding mechanism of Al/steel interface formed by laser-TIG welding assisted riveting technology

Laser-tungsten inert gas (TIG) welding assisted riveting technology was used to join Q460 high strength steel and AA6061-T651 aluminum alloy. The effect of laser power on the mechanical properties of Al/steel joints was studied. In this study, the welding-riveting hybrid structure was used to weaken the adverse effect of thermal-physical properties differences between aluminum alloy and steel, and the distribution of Fe-Al intermetallic compounds was optimized by adjusting laser power to obtain the joint with the best mechanical properties. Due to the different laser power, there were two fracture modes of Al/steel joints, namely, button-type fracture and pull-out fracture. The failure processes of these two fracture modes were discussed. Under the appropriate welding parameters, the maximum tensile shear load of the joint could reach to 6.3 kN, which was 92.2 % of the Q460 base metal. The Al/steel interface of the joint was mainly composed of Al, Fe4Al13, Fe2Al5, and alpha-Fe phases. When the favorable orientation relationships of the Fe4Al13/Al system, Fe4Al13/Fe2Al5 system, and Fe2Al5/alpha-Fe system in the Al/steel interface were selected, there was a semi-coherent-coherent-coherent matching relationship between these phases. The Al/steel interface growth model of the Al/steel joint was discussed in this study.