Toward understanding the fractured mechanism in laser welded–brazed Al/steel interface by in–situ SEM tensile observations

In laser welded–brazed Al/steel dissimilar joints, interfacial metallic compound (IMC) had a determined effect on the joint strength. Dynamics interfacial fractured behaviors and generated condition for the IMC which was most beneficial for joint strength (aimed IMC) were hardly defined. This research investigated interfacial fractured behaviors for the joints obtained different laser manufacturing parameters (pure Al, AlSi5, AlSi12 filler metals and different laser powers). In−situ tensile SEM observations was adopted to provide a dynamics observation for the interfacial fractured behaviors. Then fractured behaviors for the joint obtained under coupling parameters of filler metals and laser powers were compared and summarized. It was discovered that aimed IMC was 2–3 µm τ5–Fe1.8Al7.2Si. Then numerical simulation was carried out to calculate the interfacial thermal cycles in order to define its generated thermal condition. Based on this, activity coefficient variations of Fe–Al–Si ternary system due to the addition of alloying element were calculated so as to define its generated metallurgy condition. Experimental results and numerical simulations proved that adding 12 wt% interfacial Si content, maintaining 968°C–1003 °C interfacial peak temperature and keeping 1.64–2.63 s time interaction at high temperature were the metallurgy and thermal conditions for the generation of 2–3 µm τ5–Fe1.8Al7.2Si. This research hoped to provide a reference for determination of interfacial regulation aim in other dissimilar materials joints.