Coatings on Resistance Welding Electrodes to Extend Life

TiCP/Ni coating has been deposited onto the electrodes by electro-spark deposition to improve electrode life during resistance welding of Zn-coated steels. However, welding results revealed that molten Zn penetrates into coating through the cracks and then reacts with substrate copper alloy to form brasses. In the present work, laser treatment was performed on the TiCP/Ni coated electrodes to eliminate cracks formed in the as-deposited TiCP/Ni coating. In addition, a multi-electro-spark deposition of Ni, TiCP/Ni and Ni has also been carried out to improve coating quality. On the other hand, a TiB2 coating was also investigated. those coatings were characterized by electro-microscopy, energy-dispersive X-ray analysis, X-ray diffraction and micro-hardness tests. The results showed that cracks within the as-deposited TiCP/Ni coating could be eliminated with the use of laser treatment or a multi-layer deposition process. However, softening of copper substrate after laser treatment was a problem that restricted welding performance. Welding tests showed that the multi-layer Ni/(TiCP/Ni)/Ni coating acted as a better barrier to decrease alloying between the copper alloy and molten Zn as well as pitting (erosion) of electrode. The TiB2 coating demonstrates its potential application on the electrode to further improve the electrode's life.