Improvement of the electrical conductivity between electrode and sheet in spot welding process by direct laser interference patterning

The effort of automotive industry is the increasingly use of aluminum alloys to reduce the weight of the car. Regarding the lifetime of electrodes and the process reliability resistance, spot welding is not applied for joining of aluminum sheets. Instead, more expensive processes must be used, like riveting with supplementary component. This is caused by the electric isolating oxide layer at the sheet surface. This layer normally shows an irregular topography, causing a locale temperature increase and therefore high electrode wear. In this study, a new concept to increase the electrode lifetime and process reliability is reported. Using Direct Laser Interference Patterning, periodic surface patterns are produced at the contact area between the electrode and the sheet for influencing the contact resistance. The resulting topography and morphology are analyzed by confocal microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The electrical resistance between the contact partners copper and aluminum is measured during spot welding tests and contact resistance studies. A reduction up to 50% of the electrical resistance by treating the electrodes or an increase of more than 100 times by treating the sheets can be achieved compared to the untreated references.