Improvement of mechanical properties of DP780 steel/6061 aluminum alloy lap welded joint by introducing laser-modified Zn interlayer

The modified Zn interlayer was introduced to realise the tungsten inert gas (TIG) arc lap welding of DP780 steel (upper plate) and 6061 aluminum alloy (lower plate). The tensile shear force of the joint could be increased to more than 150 N/mm by introducing a modified Zn interlayer with a large hole diameter and hole spacing. The large hole diameter and spacing can regulate the heat conduction effect of the steel–aluminum interface, increase the welding penetration and width of the aluminum side and facilitate adequate metallurgical reactions. Moreover, allowing a certain amount of Zn vapour to escape promptly is beneficial, ensuring the stability of the interfacial melting pool and achieving high-quality welded joints.