An experimental study was carried out to detail the effects of coating Fe content on electrode life in the resistance spot welding (RSW) of galvannealed (GA) steel sheets. Scanning electron microscopy (SEM), energy dispersive X-ray (EDS), X-ray diffraction, and micro-hardness tests were employed to characterize the microstructures and property of the GA coatings and failure electrodes. The results showed that the total electrode life of the GA coating with an 11.4 wt% Fe was increased by 110% compared with a coating containing 9.6 wt% Fe. However, the total electrode life was similar when Fe content in that of coating was in the range of 7.0 to 9.6 wt%. For coating containing 11.4% Fe, microstructure composition is ? phase, ?_1 phase and continuously 5 phase. Its contact resistance is higher than for coating containing 9.6% Fe with 5 phase and ? phase and for coating containing 7.0% Fe with 5 phase, ? phase, and ? phase. Therefore, in order to obtaining the same button size, the welding current for coating containing 11.4% Fe GA steel is lowest and for coating 9.6 and 7.0% GA steel are highest. Increasing coating Fe content, the thickness of adhesion layer on the electrode surface increases. At the end of life, for coating 11.4% Fe content the thickness of adhesion layer increased to approximation 80-100 ìm with the main FeZn alloy layer formation present. During the process of spot welding, the Fe-rich alloy layer can be as a barrier layer to prevent the Cu transport from electrode face to sheets, so the growth rate of the electrode tip face may be slowly. The saw-toothed ? phase on coating surface of coating steel, then expedite alloying of the Cu and Zn and promote the tip face wear at the earlier stage.
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