Electroless nickel plating (no electrolytic nickel plating) usually has very good corrosion resistance, which includes resistance to salt spray (or brine spray). Salt spray is an environmental test that simulates corrosion in the ocean and other environments with high salt content. It is often used to assess the protection of metal coatings and coatings against corrosion.
Electroless nickel plating layer is usually composed of pure nickel and a certain percentage of phosphorus, this nickel-phosphorus alloy layer can form a dense, uniform protective layer on the surface of the substrate, thus providing excellent corrosion protection. The content of P will affect the structure of nickel coating, which has obvious influence on its corrosion resistance and mechanical properties. A higher phosphorus content (typically 8-12%) will give the nickel layer an amorphous structure, providing better corrosion resistance, but may reduce hardness.
However, the salt spray resistance of electroless nickel plating is also affected by the thickness of the nickel layer, the density, the substrate and the specific composition of the plating solution. In general, thicker coatings will provide longer protection. In addition, if the substrate beneath the coating is a metal that is prone to corrosion (such as iron or copper), a thicker layer of nickel plating may be required to ensure adequate protection.
In practical applications, in order to test the salt spray resistance of the electroless nickel plating layer, it can be placed in the salt spray test chamber for a standard salt spray test, such as ASTM B117, and then observe the corrosion of the nickel layer after a certain time. The coatings of Bigely high phosphorus electroless nickel plating process can withstand 168 hours of neutral salt spray testing without showing signs of corrosion. For more demanding applications, electroless nickel plating can also be followed by follow-up treatment, such as gold plating, chrome plating or corrosion resistant coating to further improve corrosion resistance.
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