Increase of electrode life in resistance spot welding of aluminum alloys by the combination of surface patterning and thin-film diffusion barriers

Abstract

When resistance spot welding aluminum alloys, high electrode forces are required to reduce the electrical contact resistances between the electrodes and the sheet metals. The high contact resistances and the resulting thermal load cause extensive degradation of the electrode working faces. Weld spatter occurs after only a few weld cycles, significantly reducing the quality of the weld. Conventional resistance welding machines are limited in terms of maximum electrode force and weld current. As a result, weld quality and electrode life are inadequate. The aim is to increase the achievable electrode life by surface patterning the electrode working faces and creating thin-film diffusion barriers by physical vapor deposition (PVD). Patterning is intended to penetrate the oxide layers of the aluminum sheets and increase the proportion of electrically conductive contact areas. The different influences of patterning by particle blasting and contour turning will be investigated. As a further approach, thin-film diffusion barriers of up to 3 μm are deposited on the electrodes to prevent direct Al-Cu contact. Therefore, metallic coating materials (Ni and W) and an electrically highly conductive ceramic coating material (TiB2) are investigated. The combination of electrode patterning and thin-film diffusion barriers is tested in electrode life studies. It is shown that these modified electrode working faces can limit degradation effects and contribute to an increase in electrode life. In addition, the weld quality can be improved compared to the reference condition.