Electroless ZnO Deposition on Mg-Al Alloy for Improved Corrosion Resistance to Marine Environments

Electroless ZnO (≈900 nm) was deposited on the surface of an Mg-Al alloy (AM60) to reduce its degradation in the marine environment. Uncoated and coated ZnO samples were exposed to an SME simulated marine solution for up to 30 days. The AFM and optical images revealed that the corrosion attack on the ZnO-AM60 surface was reduced due to an increase in the surface hydrophobicity of the ZnO coating (contact angle of ≈91.6°). The change in pH to more alkaline values over time was less pronounced for ZnO-AM60 (by ≈13%), whereas the release of Mg2+ ions was reduced by 34 times, attributed to the decrease in active sites on the Mg-matrix provided by the electroless ZnO coating. The OCP (free corrosion potential) of ZnO-AM60 shifted towards less negative values of ≈100 mV, indicating that electroless ZnO may serve as a good barrier for AM60 in a marine environment. The calculated polarization resistance (Rp), based on EIS data, was ≈3 times greater for ZnO-AM60 than that of the uncoated substrate.