The similar and dissimilar resistance spot weldability of 6061-T6 and 7075-T651 aluminium alloys was investigated in this study. Resistance spot weldability of commercial and aged samples in different variations was examined. The microstructure, microhardness, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electron probe micro-analyses (EPMA) were conducted to study the effects aging heat treatment had on similar and dissimilar resistance spot welded (RSW) joints. In addition, tensile shear tests were performed to determine the mechanical properties and fracture behaviour of welded joints. The tests concluded that pre-weld aging heat treatment improves mechanical properties. (c) 2012 Elsevier B.V. All rights reserved.