The thickness of coating is about 0.1mic, after the salt test, the color changed from pink to yellow. We found the content of Cu on the surface has decreased compared with inner content.
Taken as isolated, the gold-copper layer could be expected to present a fairly good corrosion resistance to chloride-containing aqueous salt solution, and selective leaching of copper should not progress to any significant extent. As this seems not the case, I suggest to carefully consider the substrate’s type of stainless steel. It is, possibly, not entirely isolated from the solution, considering also that microscopic continuity defects may possibly occur at the very thin coating layer. A widely used type of stainless steel is AISI 304. This austenitic chromium-nickel steel can be corroded by chloride-containing water. This being the case, both substrate and coating layer can be contributing for the observed enhanced corrosion effect. With a convenient type of stainless steel, e.g. AISI 316, better corrosion resistance might possibly be achieved.
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