Study of corrosion behaviour of polyurethane-ZnO/Zn composite coatings in NaCl solutions

Abstract

In order to evaluate the corrosion performance of polyurethane-ZnO/Zn coatings for LY12 aluminium alloy sheets in 3.5 % NaCl solution. Firstly, the composite coatings were prepared and the optimum stick-fill ratio was obtained. Secondly, the corrosion characteristics were characterised by SEM, EDS and electrochemistry for different immersion times and the electrochemical behaviour was investigated by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and kinetic potential polarisation curves (PP). The results show that the coating with a viscosity-fill ratio of 1:4 has a uniform distribution, the corrosion potential Ecorr is more positive, the corrosion current density icorr is the smallest, |Z|0.01Hz maintains the highest, and the coating has a good anti-corrosion performance. After soaking in 3.5 % NaCl solution for 20 days, the coating reaction resistance increased from 1.71 × 104 Ωcm2 to 6.59 × 1017 Ωcm2, and the self-corrosion current decreased from 5.12 × 10−5 A/cm2 to 5.01 × 10−7 A/cm2, indicating that the corrosion resistance of LY12 aluminium alloy sheet in the solution increased.