The effect of bath pH on electrodeposition and corrosion properties of ternary Fe-W-Zn alloy platings

As a new trial to improve the corrosion resistance of the Fe-W alloy platings, Fe-W alloys incorporating a small amount of Zn, namely novel ternary Fe-W-Zn alloy platings, are prepared by constant current electrolysis using citrate-ammonia baths. In this study, the effects of bath pH on elemental composition, morphology, plating structure, and corrosion resistance of the electrodeposited ternary alloy platings are investigated. The W content of the electrodeposited alloys showed a maximum of 31.5 at.% at pH 8.0 and an inverse correlation was observed between the W content and current efficiency in the investigated pH range. The Zn content tended to decrease with increasing bath pH, and the structure of alloy platings gradually refined along with the increase in the amount of Zn incorporated into the Fe-W alloy. Potentiodynamic polarization test results reveal fine granular structured ternary Fe-W-Zn alloy prepared at pH 8.0, containing approximately 1.6 at.% of Zn, which showed distinctly enhanced corrosion resistance in a 1 M H2SO4 solution compared to binary Fe-W alloy and ternary alloys prepared at pH 6.0, 7.0, and 9.0. It has been found that the bath pH has a great influence on the elemental composition of the ternary alloys, which significantly affects the plating structure and corrosion resistance of the alloy platings.