The dynamic resistance has been investigated during small scale resistance spot welding (SSRSW) of Ni sheets. Electrical measurements have been correlated with scanning electron microscope images of joint development. The results show that the dynamic resistance curve can be divided into the following stages based on physical change in the workpieces: asperity heating, surface breakdown, asperity softening, partial surface melting, nugget growth and expulsion. These results are also compared and contrasted with dynamic resistance behaviour in large scale RSW.

The effects of Au plating on joint formation and joint strength in small-scale resistance spot welding (SSRSW) of Ni sheets have been investigated using tensile-shear testing, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The results show that the mechanisms of the joint formation during the welding of Au-plated Ni sheets involve solid-state bonding, brazing, and fusion welding. The comparison between SSRSW of Au-plated Ni and bare Ni sheets and large-scale resistance spot welding (LSRSW) of Zn-coated steels is also discussed.

The resistance weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding (SSRSW) was studied. The effects of electrode materials and process parameters on joint strength and nugget size were investigated. The welding current ranges for SSRSW of the sheet metals were determined based on the minimum current that produced a required nugget diameter and maximum currents that did not result in electrode-sheet sticking or weld metal expulsion. A qualitative analysis indicated that resistance weldability of the metals is not only determined by their resistivity (or thermal conductivity) but is also affected by other physical properties (such as melting point, latent heat of fusion and specific heat).

The effects of Au plating on dynamic resistance during small-scale resistance spot welding of thin Ni sheets have been investigated. Compared to the small-scale resistance spot welding of bare Ni, the Au-plated material showed much lower initial static resistance, and the contribution of constriction resistance to overall dynamic resistance reduced to a negligible value very early in the welding sequence because of the low softening temperature and its lack of surface oxide film. For the same reason, the asperity heating and surface breakdown stages during resistance spot welding of bare Ni were not observed during resistance spot welding of Au-plated Ni. Furthermore, the partial surface melting stage was replaced by the solid-state bonding and brazing stages.Step increases in the sheet-to-sheet dynamic resistance curves of Au-plated Ni were shown to be due to the peripheral unzipping of a prior solid-state bond caused by uneven local thermal expansion. The electrode-to-electrode dynamic resistance curve when welding Au-plated material is not useful for monitoring the state of nugget formation.