Electrodeposition of metals on ferrous and non-ferrous substrates is a well known method for providing corrosion protection and for providing improved cosmetic appearance. Heretofore, such electrodeposition has been carried out by essentially two types of electroplating baths.
One such electroplating bath is cyanide-based. However, the use of cyanide electrolytes present significant ecological problems and require expensive waste treatment equipment. Moreover, cyanide baths are toxic and tend to embrittle certain sheets and exhibit low current efficiencies.
In an effort to overcome the deficiencies of the cyanide baths, chloride-based zinc baths of essentially three types were developed. These three types of baths were termed neutral, ammonia based and non-ammonia based. Although these chloride-based baths eliminate the toxicity problem of the cyanide baths, these baths also have other limitations. The neutral and ammonia based baths contain excessive amounts of ammonium ions and/or chelates, thereby making metal removal costly and difficult. The non-ammonia based baths generally result in deposits which are brittle at thicknesses over 0.5 mils and which flake at thicknesses less than 0.5 mils. Furthermore, iron co-deposition, which causes a dull appearance and poor corrosion protection, is a problem with all chloride-based baths.
Examples of such chloride-based zinc baths are discussed in detail in U.S. Pat. Nos. 4,070,256; 3,694,330; Re. 27,999; 3,729,394; 3,730,855; 3,838,026 and 3,855,085 (all incorporated herein by reference). Although the foregoing patents disclose chloride-based zinc baths, they do not disclose a zinc-nickel alloy bath. Zinc-nickel alloy electroplating is advantageous over conventional zinc electroplating in that it provides superior corrosion resistance, minimization of iron codeposition and ductile deposits at thicknesses over 0.5 mils.