Electrode worksheet interface behaviour during resistance spot welding of Al alloy 5182

Resistance spot welding of aluminium alloy 5182 with spherical tip electrodes was investigated. Surface interaction between electrode and worksheet was focussed to understand the pitting behaviour of electrode. Both experimental work and finite element analysis were employed. It was found that the interaction between electrode tip and worksheet surface that occurred during the load ‘squeezing’ phase of the welding sequence of resistance spot welding process had a significant effect on the electrode pitting behaviour. At this interface, squeezing caused surface shear stress that strongly suggested the possibility of slip at the periphery of the contact region. This suggestion of slip was consistent with disrupted oxide layer and reduced electrical contact resistance near the periphery of the contact. At the beginning of the current phase, current concentrated near the periphery caused high constriction resistance which resulted in alloying, pickup and eventually pitting of electrode in a ring around the contact centre.