Abstract: Electrodes used for spot welding of aluminium workpieces are improved by a combination of steps:(a) A roughened surface is formed on the electrode tip, preferably to an average roughness depth of 12 to 30 microns.(b) also an artificial protective coating, e.g. a chromate-based coating or an anodic oxide film, is applied to the workpieces.(c) Optionally the nugget diameter in the initial welding set-up is arranged to be not more than 15% greater than the minimum acceptable.Features (a) and (b) act synergistically to increase the service life of the electrodes, typically to more than 2000 welds.

Abstract: The invention concerns a method of forming a joint between aluminium workpieces. These carry an artifically applied e.g. chromate or anodic oxide coating on their surface. A curable adhesive containing up to 40% by weight of particulate filler having a maximum particle size of 300 microns is provided between the workpieces to be joined. Resistance welding is performed using a welding electrode whose tip has a surface with an average roughness depth of at least 10 microns. This increases electrode life and makes it possible to use lower welding currents than previously recommended.