Performance of resistance spot weld caps coated with Ni and Fe aluminide alloys by electro spark deposition on hot dip galvanized steel

Resistance spot welding (RSW) is widely used as a main joining technique in industry and the electrode caps are frequently replaced because of the degradation during service. In this study, the G type copper RSW electrode caps were coated with Fe and Ni based Fe3Al, FeAl, Ni3Al, NiAl alloys by Electro-Spark Deposition (ESD), providing resistance to hot deformation, oxidation and Zn evaporation from sheet metal. The ESD coated electrode caps were tested in-situ on a hot dip galvanized steel in order to assess the performance of RSW electrode caps. For this purpose, three different coating voltages were selected for each coated electrode, and 12 different cap coatings were produced in total. Fifty resistance spot welds were consecutively manufactured with the same parameters for each type of coating electrodes. Hardness measurements, macrostructural examination, Ultrasonic Testing (UT) and chisel tests were performed on welded samples produced. In addition, effects of different coatings on RSW electrode caps were investigated on microstructural development, hardness variations and deformation capacity of resistance spot welds. Results showed that chisel tests and cross section thickness values of the welded sample made with the caps that were ESD coated with the Ni3Al electrode produced better results than the other caps. The cross-sectional thickness of nuggets was lower in all 158 V coated caps. The performance of aluminide coatings on RSW electrode caps can be listed from the best to the worst in the order of Ni3Al, NiAl, Fe3Al, and FeAl.