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| Zinc-nickel is the most popular zinc alloy used today. A typical deposit will have between 6-10 % by weight nickel. Higher concentrations of nickel will prevent the coating from being chromated. A deposit with a concentration of nickel above 15% by weight will be more passive than the base material and will not offer galvanic protection. Zinc-nickel deposited from an alkaline bath will have a columnar structure which provides for superior formability as compared to baths that are acid based. Acid baths produce a laminar structure which will not perform well after forming. Zinc-nickel has the highest corrosion resistance of all the zinc alloys except in the presence of sulfur dioxide. When sulfur dioxide is in the corrosion environment tin-zinc is the better coating. Zinc-nickel has a high resistance to heat and will retain its corrosion resistance even after being exposed to elevated temperatures. Normal zinc plating and other zinc alloy plating will have the corrosion resistance compromised when exposed to elevated temperatures. Zinc-nickel can be safely used as a substitute for cadmium on steel fasteners when they are to be in contact with aluminum. |