Failure analysis of TiB2–TiC composite-coated electrodes for spot-welding galvanised steel plates

Abstract

In order to improve the lifespan of electrodes used for spot-welding galvanised steel plates, electrodes coated with TiB2–TiC composite were studied. Scanning electron microscope and X-ray diffraction were employed to analyse the failure process of TiB2–TiC composite-coated electrodes when they were used for spot-welding galvanised steel plates. The analysis results show that the influence of mechanical force and welding heat, along with other factors, could lead to the generation of cracks in the originally complete TiB2–TiC composite coating. The developed cracks weave into a mesh, which enhances the extent of alloying between the TiB2–TiC composite-coated electrode and the zinc coating of the galvanised steel plate. Because of the influence of local alloying, the coatings tend to peel off in pieces, resulting in a higher level of alloying and the final failure of TiB2–TiC composite-coated electrodes. Failure of TiB2–TiC composite-coated electrodes is the result of both alloying and plastic deformation.