Electrodeposition of Zn with Mg was tried using the rotating cylindric cathode in sulfate solutions containing Zn2+, Mg2+ and quaternary ammonium salt at 60°C under galvanostatic conditions. Mg was codeposited with Zn when the Zn deposition was significantly suppressed by the addition of stearyle benzyl ammonium chloride (C18-Benzyl) to the solution. The content of Mg in deposits was increased with an increase in the polarization of Zn deposition by additive C18-benzyl. The content of Mg in deposits was related to the content of C18-benzyl in deposits. XPS spectra of the deposits showed that Mg element in the deposits existed in bivalent state at low flow rate. However, in the deposits at high flow rate, the peak of Mg2s spectrum existed between bivalent and metallic Mg, suggesting that the chemical state of Mg may be changed depending on the flow rate. The duration to red rust occurrence in salt spray corrosion test was five times longer in Zn-0.4%Mg electroplated steel sheet than in electrogalvanized steel sheet.
