Improvement of tensile and deforming abilities of Al/steel laser welded-brazed joints by addition of Si

Al/steel structural parts have significant potential for application in electric vehicles (EVs). 6061 aluminum alloy jointed to DP590 steel in butt configuration successfully using laser weld-brazing with filler wires of varying Si content. Si can participate in interfacial reactions, inhibiting the bonding of Fe to Al and reducing the formation of brittle IMCs. Meanwhile, Si can replace the Al atoms in Fe-Al IMC, forming a less brittle Fe-Al-Si phase and reducing the thickness of IMC. Increasing the si content improves the joints’ tensile strength and bending properties. The Si substitution behavior of Al was clarified using first-principles calculations based on density functional theory. The computational results revealed that substituting Al atoms with Si atoms resulted in lower formation enthalpies and binding energies, indicating enhanced thermodynamic stability. Furthermore, the introduction of Fe-Si covalent bonding and the Si substitution behavior reduced the covalency of the IMCs, leading to a softening effect and reducing the hardness of the interface. Depending on the hardness of IMCs, the joints exhibited different fracture behaviors in the tensile and bending tests. The joint produced with AlSi12 filler wire demonstrated superior tensile strength and bending properties, achieving values of 143.1 MPa and 40.8°, which were 45.7 % and 57.5 % higher than those of the joint produced with pure Al filler wire (98.2 MPa and 25.9°).