Research On Corrosion Resistance Of Several Kinds Of Electric Arc Spray Coatings In Simulated Marine Environment

In recent years,with the development and utilization of a large number of marine resources,various kinds of offshore platforms have been built.They have been exposed to salt spray,moisture and seawater environment for a long time,and are extremely vulnerable to serious corrosion.The commonly used corrosion protection methods include:metal coatings,organic coatings,and electrochemical protections,etc.,among which thermal spraying metal coatings are widely used in marine anti-corrosion environments due to the low cost,high efficiency and significant anti-corrosion performance.At present,the researches on arc spray coatings mainly focus on pure aluminum and zinc aluminum coatings.Compared with pure aluminum coatings,5000series and 6000 series aluminum alloys have the advantages of high hardness,good corrosion resistance and good wear resistance.However,there are only a few reports on aluminum alloy coatings,and there is still a lack of systematic research.In this paper,pure aluminum coating,5083 aluminum alloy coating,6061 aluminum alloy coating and Zn15Al coating were prepared on the surface of EH36 steels by arc spraying technology,as well as 2205 stainless steel coating and 2507 stainless steel coating for comparison,to evaluate the corrosion resistance of each coating.The salt spray tests were used to simulate the marine atmospheric environment,and the full immersion tests simulated the seawater immersion environment.The corrosion resistance of six coatings were contrastively studied by SEM,XRD,physical property tests and electrochemical tests.As a result,the 5083 aluminum alloy coatings and Zn15Al coatings were screened out as test coatings for in-depth corrosion mechanism analysis.The results of corrosion loss in simulated marine atmosphere show that the corrosion rates of 5083Al alloy coating are significantly lower than those of Zn15Al coatings.The analysis and characterization results show that the corrosion products of 5083 aluminum alloy coatings are mainly Al（OH）₃,and the corrosion products are dense and blocky.The corrosion products of Zn15Al coatings are mainly composed of Zn（OH）₂ and Zn₅（OH）₈Cl₂·H₂O,which present loose fine needles.EI tests show that the 5083aluminum alloy coatings have higher impedance film value than the Zn15Al coatings,which is consistent with the results of corrosion weight loss.In simulated seawater immersion environment,the corrosion behaviors of the two coatings show that,the initial corrosion rates of 5083 aluminum alloy coatings are higher than those of Zn15Al coatings,and the corrosion rates in long-term corrosion are lower than that of 5083 aluminum alloy coatings.In the early stage,due to the large potential difference between the inclusions and the matrix in 5083 aluminum alloy coatings,the corrosion rates of 5083 aluminum alloy coatings are higher,whereas,Zn15Al coatings generate a large number of corrosion products rapidly in the early stage of corrosion,so as to protect the coating matrix.With the extension of corrosion time,by the observations of cross-sectional morphologies and the theoretical calculations of corrosion product constant,it can be obtained that 5083 aluminum alloy coatings are more inclined to form dense corrosion products layers.On the contrary,the surface corrosion products layers of Zn15Al coating are less protective.