Role of Si element in the IMC formation and tensile-shear property of the laser welding-brazing steel-Al dissimilar joints

•The addition of Si could improve the tensile-shear property of steel-Al joints.•Si changed interface microstructure from brittle Fe-Al IMCs to ductile Fe-Al-Si IMCs.•Fe-Al-Si IMCs resisted crack propagation, guaranteeing the qualified joint strength. A comparative investigation was conducted to explore the role of Si in the intermetallic compound (IMC) formation and tensile-shear property of steel-Al joints fabricated via laser welding-brazing (LWB) technique. Three filler wires including ER5356, ER4043 and ER4047 were employed to join the DP780 steel and 5754 Al alloy. The results exhibited that the presence of Si could improve the tensile-shear property of steel-Al joints. With increasing the Si addition, the failure locations of the joints changed from the interface, weld metal to Al alloy base metal. For the joints fabricated with ER5356 filler, the IMCs consisted of Fe2Al5 and Fe4Al13. On the contrary, Fe4(Al, Si)13 and Al8Fe2Si was detected for the joints prepared with ER4043 and ER4047 filler wires. The Si could suppress the generation of brittle Fe2Al5. In addition, Fe4(Al, Si)13 and Al8Fe2Si could resist the crack propagation, guaranteeing the qualified tensile-shear strength of the joints.