Substantial electrode life enhancement in resistance spot welding of galvanised steels through nanolayered multi-layer CrN/(Cr,Al)N coating

Abstract

The short electrode life is one of the most important problems associated with resistance spot welding of galvanised steel sheets. In this study, a nanolayered multi-layer CrN/(Cr,Al)N coating was deposited on the tip of the electrode by applying the cathodic arc physical vapour deposition process with the layer thickness of about 30 nm and an overall thickness of 1.1 µm. The electrode life test confirmed that the coating could extend the electrode life up to 125%. The coated electrode showed a significantly lower growth rate (∼0.3 µm per weld), in comparison to the un-coated one (∼1 µm per weld). The degradation of the electrode could be subdivided into two subsequent steps: the degradation of the electrode periphery and the degradation of the electrode tip. The CrN/(Cr,Al)N coating could effectively protect the electrode tip periphery from zinc adhesion and postpone the first stage electrode degradation which delayed the second one.