Corrosion life evaluation of organic/zinc composite coatings in water-saturated acid soil using electrochemical impedance spectroscopy

The corrosion behaviour and service life of organic/zinc composite coatings in water-saturated acid soil were investigated using electrochemical impedance spectroscopy (EIS) and open-circuit potential (OCP) measurements. For the duplex system, the service life of the organic topcoat (Lf) was determined to be 1050 days, and that of the underlying zinc coating (Lz) was 390 days. Based on these results, a two-step life prediction method is proposed: Lc = k(Lf + Lz), where the empirical constant k ranges from 1.5–2.3. This yields an overall accelerated lifetime of 2160–3312 days for the organic/zinc composite coating. The proposed method offers an efficient framework for evaluating the durability of organic/metal composite systems.