Improvement of aluminium alloy and polymer single sided coaxial resistance spot welded joint with steel cover plate

A reusable steel cover plate was introduced into the aluminium alloy/nylon dissimilar materials single sided coaxial resistance spot welding process, to address the alloying between the electrode welding surface and aluminium alloy workpiece, which limited the continuous increase in heat input, thus further limited the serviceability of the welded joint. Three-dimensional numerical simulations were employed to investigate the variations in current conduction, heat generation and heat distribution during the welding processes with and without the introduction of the steel cover plate. With the introduction of the steel cover plate, the main heat production area changed from the copper electrode/aluminium alloy workpiece interface to the steel cover plate and the copper electrode/steel cover plate interface, and the temperature distribution on the aluminium alloy workpiece presented a more uniform state. Nylon melted and spread more on the aluminium alloy surface, thus accordingly, the average peak tensile shear load was expanded from 2.6 kN to 4.1 kN, with an enhancement of 57.7% at a welding current of 7.5 kA.