Development of thermal spray coatings with corrosion protecting and antifouling properties

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For the purpose of development of thermal spray coatings with both corrosion protection and antifouling properties, aluminum-copper coatings, aluminum-zinc coating and zinc coatings are sprayed onto a steel substrate and are immersed in the sea. Some of the substrates are treated with an aluminum under-coat prior to the spraying of the above-mentioned coatings(top-coats). While barnacles adhered to the aluminum-copper alloy coatings of copper content lower than 20 mass% and to the aluminum-copper blend coatings of the copper content lower than 40 mass%, rusting of the steel substrates occurred in the case of the coatings of higher copper content. The zinc coatings and aluminum-zinc coatings containing more than 50 mass% zinc possess both corrosion protection and antifouling characteristics. It was found that the application of the aluminum under-coat promotes the corrosion of the top-coats themselves. In this case, the corrosion started on or near the top-coat/under-coat boundary or the under-coat/substrate boundary. The corrosion product(s) lift the top-coats and are also accumulated on the top-coats.