Tin-Manganese Alloy Electrodeposits

Abstract

The corrosion performance of tin-manganese alloy electrodeposits either immersed in a quiescent sodium chloride solution or exposed to neutral salt spray (NSS) was studied. The results obtained were then compared with those for conventional pure zinc and zinc-nickel alloy electrodeposits with or without chromate passivation treatment. It was found that tin-manganese alloy electrodeposits provided much longer sacrificial protection against the corrosion of mild steel substrates than zinc-nickel alloy coatings, although they were inferior to pure zinc coatings. The prolonged sacrificial property was attributed to the high polarization resistance of tin-manganese alloy electrodeposits as revealed by linear polarization resistance techniques, which would only allow the corrosion and the consequent ennoblement of these coatings to proceed at a slow rate. The result of NSS tests indicated that tin - manganese alloy electrodeposits, with a time to red rust of about 1200 h, were as good as chromated zinc-nickel alloy coatings but far outperformed pure zinc coatings and nonchromated zinc-nickel coatings. The high corrosion resistance of tin-manganese alloy electrodeposits without any passivation treatment suggests that they may be an environmentally friendly replacement to zinc alloy coatings, which need toxic chromate conversion coatings for corrosion-resistance enhancement. (c) 2007 The Electrochemical Society.