A method for improving resistance spot weldability is proposed based on creating a differential surface resistance between the sheet surfaces. The differential in surface resistance is achieved by an anodizing technique. Relationships between electrode life, differential surface resistance and differential oxide thickness have been established. Under the conditions used, optimum electrode life is achieved with a differential oxide thickness of some 330Å. This corresponds to a differential in surface resistance of approximately 50 × 103 micro-ohms. The treatment also produces an improvement in the consistency of weld performance. Although the method has so far only been tested and evaluated on a laboratory scale it is felt that the results offer sufficient insight into the mechanisms of aluminum spot welding to merit publication. The possibility of developing a commercial process based on these findings for the production of improved autobody sheet is under investigation.