Electrodeposition and characterization of tin-zinc alloy coatings

This paper reports the electrodepostion of tin-zinc alloy coatings from a non-cyanide alkaline stannate/zincate bath formulation containing a complexing/stabilizing agent. The bath also comprises addition agents which considerably improve the coating properties and give a semi-bright finish. The effects of variables of the process on deposit composition were studied. The 25 +/- 5% zinc (balance tin) alloy coatings offer excellent corrosion protection with no obvious white corrosion product. The deposit offers protection which is better than cadmium, zinc and zinc-nickel alloy coatings for equal thicknesses. The tin-zinc deposit obtained from the stannate/zincate bath is fine grained, semi-bright, and shows considerable improvements over the tin-zinc deposit from the previously used cyanide plating process. Election microscopy and X-ray methods reveal microstructural information and structure-corrosion properties of these alloy coatings.