Fatigue properties and fracture behavior of Al/steel butt joints fabricated by laser-MIG welding-brazing

Robust 2-mm 6061-T6/SUS304 butt plates were obtained using laser-MIG hybrid welding-brazing technology. The fatigue properties and fracture behavior of Al/steel welding-brazing joints were first discussed. Due to the change in the fracture mechanism, the weld reinforcement improved the fatigue strength, which was higher than that of the Al/steel joints using the solid-state welding method. This strengthening effect was very different from traditional fusion welding joints with reinforcement. The fatigue test results showed that the fatigue strength of the Al/steel joints with reinforcement reached about 105 MPa at 10(6) cycles. After removing the weld reinforcement, the fatigue strength of the Al/steel joints reduced significantly to 55 MPa. The existence of reinforcement also led to different fatigue fracture behaviors. In the Al/steel joints with reinforcement, the fatigue fracture mode changed with increasing cyclic stress load, and the fatigue crack initiation zone was inclined to begin at the weld toe and then propagated along the weld at a lower stress load. Fatigue crack initiation sites moved to the aluminum weld near the interface and spread along with the IMC layer and the aluminum weld at higher stress loads. After removing the weld reinforcement, only the interface fracture mode was found.