Composition control of tin-zinc deposits using experimental strategies

The robust electroplating settings of a direct-current (dc) plating mode for the co-deposition of Sn-Zn deposits with their composition close to the eutectic point (i.e., Sn-9Zn) from the chloride solutions were achieved and investigated by using experimental strategies, including the fractional factorial design (FFD) and central composite design (CCD) coupled with the response surface methodology (RSM). The temperature of the plating bath, pH, and the metallic ion ratio (i.e., Sn⁴⁺/Zn²⁺ ratio) were found to be the key factors affecting the composition of Sn-Zn deposits in the FFD study. The effects of pH and temperature of the plating solution on the composition of Sn-Zn deposits were examined using a regression model in the CCD study. This model, represented as contour plots, showed that pH 5.0 and temperature = 78 °C were the robust electroplating settings for the co-deposition of the eutectic Sn-Zn alloys, which was independent of the substrates. In addition, based on the robust plating settings, the composition of Sn-Zn alloys could be precisely controlled and predicted by adjusting the composition of the plating baths. From the morphologies and crystalline information, the binary Sn-Zn deposits prepared in this work should belong to heterogeneous alloys.