SECM and EIS Studies of Galvanic Corrosion of Copper/Iron Connected to Automotive Parts in Seawater

The electrochemical behavior of galvanic coupling between copper and iron was investigated in natural seawater by SECM and EIS. The accumulation of metal complexes on the sample prevents the steep decrease in the resistance of film (R f ) and charge transfer (R ct ). It was shown that the film resistance, R f of sample is decreased from 1.37 × 10 4 Ω cm 2 at 1 day to 7.51 × 10 3 Ω cm 2 at 15 days. Similarly, there is a decrease in R ct from 2.95 × 10 4 Ω cm 2 at 1 day to 1.57 × 10 4 Ω cm 2 at 15 days with increase in test time. On the other hand, the double layer capacitance is increased from 157.4 µF at 1day to 977.8 µF at 15 days. Similarly, the film capacitance is also increased from 40.4 µF at 1 day to 123.7 µF at 15 days. The Fe 2+ ions at + 0.60 V Cu + ions + 0.34 V are detected. The tip current at iron is 14.8 nA at 1 day (light pink) and reached 6.0 nA at 15 days (greenish yellow). This indicates that the deposition of metal complexes at the sample slows down the iron oxidation further. After corrosion testing, the enrichment of corrosion products of Cu and Fe at the sample was analyzed by SEM/EDX. FIB-TEM analysis confirms the rust layer containing Cu and Fe in the rust. The corrosion protection performance has been enhanced by nanoscale corrosion products deposition on the sample. Graphic abstract