Copper-nickel plating is divided into electrolytic nickel plating and chemical nickel plating. Electroless nickel plating is to deposit a uniform and compact nickel coating on the cathode (plated part) in an electrolyte composed of nickel salt (called main salt), conductive salt, pH buffer and wetting agent, with metal nickel as anode and direct current as cathode. Bright nickel is obtained from plating solution containing brightener, while dark nickel is obtained from electrolyte without brightener.
The general content of high-sulfur nickel is 0. 12~~0.25%. The electrochemical activity of this nickel is higher than that of copper, copper-tin alloy, dark nickel, bright nickel, semi-bright nickel and chromium. High sulfur nickel coating is mainly used as the intermediate layer of protective and decorative composite coating on steel and zinc alloy substrate. The principle is that the sulfur content of bright nickel in the upper layer is higher than that of semi-bright nickel in the lower layer.
Therefore, the potential difference between the two layers is100 ~140 mv, which makes the double-layer nickel change from vertical corrosion of single-layer nickel to horizontal corrosion, and constitutes electrochemical protection for steel matrix.
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Nickel plating has a wide range of applications, which can be used as a protective and decorative coating to protect the matrix material from corrosion or to brighten and decorate the surfaces of steel, zinc die castings, aluminum alloys and copper alloys. It is also often used as an intermediate coating of other coatings, which is plated with a thin layer of chromium or a layer of imitation gold, which has better corrosion resistance and more beautiful appearance.
In functional application, the thickness of nickel plating on parts in special industries is about 1~3mm, which can achieve the purpose of repair. In particular, it is widely used in the manufacture of continuous casting crystallizer, electronic component surface mold, alloy die casting mold, aero-engine parts with complex shapes and microelectronic components.
References:
Baidu encyclopedia-nickel plating