Research On Galvanic Corrosion Behavior Of Ship Typical Materials

Seawater is recognized to be strong corrosive media for metal. With application of new materials on ships, galvanic corrosion between different materials with different electrochemical properties cause great financial loss. Therefore, the study of galvanic corrosion behaviors and protection methods in the marine environment is of great significance.Three couples comprised of 921A, B10 (90:10cu/ni alloy) and TA2 are studied in seawater with different dissolved oxygen content and different temperature at different area ratio. The galvanic corrosion behavior is investigated with dynamic polarization method, electrochemical impedance spectroscopy (EIS),galvanic corrosion monitoring and weight loss experiment, together with environmental scanning electron microscopy(ESEM) to observe Surface morphologies of the samples and XRD to analyze corrosion products.The research shows that 921A corrosion isn't accelerated when coupled with TA2, due to insignificant cathode effect of TA2 caused by high oxygen overpotential. The corrosion mechanism of 921A/B10 is the same as 921A/TA2, so is the corrosion rate of the two couples. It is found that the galvanic effect can be neglected in seawater with low dissolved oxygen content; The corrosion rate of anode increases with dissolved oxygen content and temperature. Increase of temperature accelerates oxygen diffusion ,at the same time, it will reduce oxygen solubility and promote formation of calcium deposits, the corrosion rate of 921A/B10 shows extreme value at 45℃. The limited area ratio value for 921A/B10 and 921A/TA2 is 400.When surrounding is aerated with gas, the passive film of low potential difference couple (B10/TA2) behaves unstable and has low capability of self-repairing. Dissolved oxygen content and temperature have no appreciable impact on B10/TA2. and the corrosion will not be aggravated if the area ratio is suitable.Combining coating with aluminum sacrificial anode protection can achieve better protection effect. Sacrificial anode can reduce galvanic potential, give effective protection to the anode of couples. But the changing regularity of cathodic protection current as same as the layout and dosage of electrode still need further research.