The standard electrode potential of zinc is -0.76V, which is a typical sacrificial anode protective coating for steel substrates. Zinc alloy coating is a further development of electro-galvanized coating. By adding nickel, tin, cobalt, chromium and other alloying elements, it not only maintains the sacrificial anode protection characteristics of zinc coating, but also makes the coating The performance, especially the corrosion resistance, can be greatly improved.
Zinc-nickel alloy plating technology is a kind of zinc alloy plating. The zinc-nickel alloy coating containing 25-30% nickel has good corrosion resistance and mechanical properties, but the internal stress is large. The zinc-nickel alloy coating containing 10-20% nickel has good corrosion resistance and mechanical properties, and is resistant to seawater and moisture. It is 6~7 times higher than zinc, and the zinc-nickel alloy coating containing 7~9% nickel can be formed and processed after plating, and is easy to passivate.
Beijing University of Science and Technology has developed the following two types of zinc-nickel alloy plating technology.
Zinc-nickel alloy coated steel sheet has been valued as a highly corrosion-resistant surface-treated steel sheet for automobiles since the 1980s, and high-speed electroplating technology for zinc-nickel alloy coated steel sheet has been developed for this purpose.
The high-speed electroplating technology uses a simple sulfate-based plating solution system to conduct electroplating at a high current density of more than 50 amperes/square decimeter while the steel plate is running at a high speed of about 100 m/s. The current efficiency is over 95%.
The coating contains 10-20% nickel, and the phase structure of the coating is a single γ phase with the best corrosion resistance.
2. Conventional zinc-nickel alloy coating electroplating technology
The zinc-nickel alloy coating electroplating technology developed by the conventional ammonium salt weak acid plating solution system has obtained a national patent. Electroplating is carried out at a current density of 1-5 amps/dm2, the coating is bright and the color tone is similar to that of stainless steel, but the cost is low. The corrosion resistance of the obtained zinc-nickel alloy coating is 5-10 times that of the electro-galvanized coating, and the heat resistance is greatly improved compared with the zinc coating.
Application
As a high corrosion-resistant protective layer for automobile bodies and other mechanical equipment and parts, it can improve the corrosion resistance of original galvanized parts. It can be used as a decorative corrosion-resistant coating imitating stainless steel, as a heat-resistant decorative protective layer for the inner body of a microwave oven, and as a condensation and heat dissipation part of a refrigerator.
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