The spot weldability of zinc vapor-deposited steel sheets (VZ) and galvannealed steel sheets (VZA) was investigated. Weldability lobes of VZA are approximately equal to those of hot-dip galvannealed sheets, and broader than those of VZ or hot-dip galvanized sheets. Electrode life depends on both welding conditions and surface conditions, but is independent of both the coating process, (i.e., zinc vapor deposition, hot-dip galvanizing, electro-galvanizing) and the alloying process. Electrode life increases with increasing welding current and electrode tip diameter, but decreases with increasing welding time and coating weight. Electrode life in the welding of VZA is 1.4-1.6 times longer than in the case of VZ. Γ phase (Fe
3Zn
7), γ phase (Cu
5Zn
8) and β phase (CuZn) are observed at the electrode faces for welding both VZ and VZA, γ phase is so brittle that its growth rate affects electrode wear. A high rate of growth of γ phase and a narrow weld current range both contribute to short electrode life when welding VZ and heavy coated VZA.
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