Evaluation and comparison of throwing power in zinc electroplating baths

Uniformity of metal deposition is crucial in electrodeposition processes since it directly influences coating performance, corrosion resistance, and mechanical durability, especially for components with complex geometries. This study evaluates and compares the throwing power (TP) and throwing index (TI) of three commonly used zinc electroplating baths —chloride, sulphate, and acetate- under controlled conditions. A Haring-Blum cell was used for TP measurements, and TI values were calculated from metal distribution ratios across different cathode distances. Potentiodynamic cathodic polarization curves were also recorded to help correlate electrochemical behavior with deposition uniformity. The zinc chloride bath consistently demonstrated superior TP (14.28 – 60.0) and TI (1.33–4.0) across a wide range of zinc salt concentrations, current densities, and pH values, owing to its higher conductivity and enhanced polarization behavior. Sulphate-based baths exhibited moderate TP (5.26–33.33) and TI (1.0–2.32) with significant sensitivity to operating conditions, whereas acetate-based baths exhibited the lowest TP (5.26–14.28) and TI (1.0–1.66), most likely due to limited ion mobility and conductivity. Microstructural and surface characterization confirmed these findings, with the chloride bath exhibiting the most balanced performance in terms of hardness, morphology, and coating uniformity. These results lay the groundwork for improving zinc-electroplating baths to achieve better coating longevity, corrosion resistance, and dependable performance in industrial applications that demand high surface coverage and exact thickness control.