Investigating the influence of Ni interlayers on Fe/Al laser welded joints: A first-principles study

201 Stainless steel and 5052 aluminium alloy were laser lap welded, both with and without a Ni foil interlayer. The Ni addition enhanced the metallurgical reaction between molten stainless steel/aluminium, resulting in the formation of the Al0.9Ni1.1 intermetallic compound. First-principles calculations estimated the equilibrium lattice and properties of IMCs (intermetallic compounds). A structural model of the interface revealed that the bonding strengths of Al/IMC and Fe/IMC interfaces surpassed those of IMC/IMC interfaces, making cracks prone to initiate and expand at the latter. Joints without Ni reached a max tensile shear strength of 74.5 N/mm, while those with Ni increased significantly to 101.8 N/mm, marking a substantial 36.6% enhancement.