Surface modification of resistance welding electrodes by electro-spark deposited coatings

To improve electrode life during resistance welding of Zn-coated steels, TiCP/Ni coatings were deposited onto the surface of electrodes by electro-spark deposition. In addition, laser treatment was performed to eliminate cracks formed in the as-deposited TiCP/Ni coating. Properties of the coatings were characterized by electro-microscopy, energy-dispersive X-ray analysis, X-ray diffraction and micro-hardness tests. The results showed that cracking occurred within the as-deposited TiC P/Ni coating. The cracks of the coating could be eliminated with the use of a multi-layer deposition process using Ni and TiCP/Ni layers. Although laser treatment of TiCP/Ni coating could eliminate cracks, the softening of copper substrate after laser treatment was a problem that restricted welding performance. Welding tests showed that alloying between copper alloy and molten Zn as well as pitting (erosion) of electrode were significantly reduced due to the barrier action of the coatings, especially with multi-layer Ni/(TiCP /Ni)/Ni coating on the electrode surface.