Electrochemical Performance and Corrosion Protection Efficiency of Zinc-Based Protective Coatings on Mild Steel

Abstract

Corrosion of mild steel remains a major challenge in industrial and marine environments due to its adverse effects on structural integrity, maintenance costs, and service life. This study investigated the electrochemical performance and corrosion protection efficiency of electrodeposited zinc coatings on mild steel in a 3.5 wt.% NaCl solution. Mild steel specimens were electrodeposited with zinc under controlled conditions and evaluated using Open Circuit Potential (OCP), potentiodynamic polarization (Tafel), and electrochemical impedance measurements. Corrosion potential (Ecorr), corrosion current density (Icorr), polarization resistance (Rp), corrosion rate, and coating protection efficiency were determined to assess coating performance. The electrochemical results demonstrated that zinc electrodeposition significantly enhanced the corrosion resistance of mild steel. The corrosion current density decreased from 18.5 µA cm⁻² for bare mild steel to 4.8, 2.6, and 1.7 µA cm⁻² for Zn-10, Zn-20, and Zn-30 coatings, respectively. Simultaneously, polarization resistance increased from 420 Ω cm² for the uncoated substrate to 1650, 2840, and 3980 Ω cm², while the corrosion rate decreased from 0.214 mm year⁻¹ to 0.056, 0.031, and 0.020 mm year⁻¹, representing an overall reduction of approximately 90.7%. The coating protection efficiency increased progressively from 74.1% for Zn-10 to 85.9% for Zn-20 and reached a maximum of 90.8% for Zn-30. The open circuit potential shifted towards more negative values with increasing coating quality, confirming the sacrificial anodic behaviour of zinc. The improved corrosion resistance was attributed to the combined effects of galvanic protection, barrier action, and the formation of stable zinc corrosion products that inhibited electrochemical reactions at the steel/electrolyte interface. Overall, the Zn-30 coating exhibited the best electrochemical performance, demonstrating that optimized zinc electrodeposition is an effective and economical corrosion protection strategy for mild steel used in aggressive industrial and marine environments.