Among zinc-based alloys, zinc-nickel alloy coatings are a new type of excellent protective coating for use in harsh industrial environments and harsh marine environments. The corrosion resistance of zinc-nickel alloy with nickel content of 7~9% is more than three times that of zinc coating; the corrosion resistance of zinc-nickel alloy coating with nickel content of about 13% is more than 5 times that of zinc coating, which has the best corrosion resistance
Due to its high corrosion resistance, low hydrogen embrittlement, weldability and machinability, zinc-nickel alloys have attracted great attention and have been widely used. Zinc-nickel alloy coating has high melting point and is suitable for electroplating of automobile engine parts. It is small in hydrogen embrittlement and suitable for electroplating on high-strength steel. It can be used as cadmium-plated coating and is mostly used in military products.
Zinc-nickel alloy plating baths are mainly divided into two types: one is a weak acidic system, and the plating solution is simple in composition and high in cathode current efficiency (generally above 95%). The plating solution is stable and easy to handle. The other is alkaline zincate plating solution, the main advantages of which are: good dispersion of plating solution, uniform proportion of coating alloy in wide current density range, uniform thickness of coating, less corrosion to equipment and workpiece. The process is stable, easy to operate and of low cost.
Corrosion resistance. Zinc and zinc-nickel alloys are used as functional coatings. Zinc-nickel alloys are far superior to galvanizing in corrosion resistance, which is the main reason why researchers spend a lot of time developing zinc-nickel alloys. After being passivated by color passivation, the zinc-nickel alloy coating layer can easily pass through 1000 hours without neutral rust under neutral salt spray, and the galvanized layer can pass through color passivation and pass for 120 hours. The zinc-nickel alloy coating after white passivation can pass through 400 hours without neutral rust under neutral salt spray, while the galvanized layer after blue and white passivation can pass for 96 hours.
Appearance. In general, the zinc-nickel alloy color passivation layer is not as bright as the galvanized layer, especially when the nickel content in the alloy coating is high; the zinc-nickel alloy after white passivation color is not as white as the galvanized layer. However, people's understanding of things is often preconceived, as is the color of the product. With the increase in zinc-nickel alloy products on the market, people have been able to accept the difference in color between the zinc-nickel alloy passivation layer and the galvanized passivation layer.
Production costs. Since the zinc-nickel alloy coating contains about 13% of nickel, the price of nickel is much higher than that of zinc, so the electroplated zinc-nickel alloy is much more expensive than electrogalvanizing.
Process maintenance. Alkaline zincate galvanizing has now been widely accepted in the market, and the zinc-nickel alloy process as a "new" electroplating process has not yet been widely used. In fact, zinc-nickel alloy has been used in the market for more than 20 years and is developing rapidly. The process is now quite mature and its stability is even better than galvanizing.