Magnesium and magnesium alloys have high electrochemical activity, that is, high oxidation tendency, and most acidic solutions have strong corrosion effect on them, which makes the electroplating of magnesium alloys have a series of characteristics. Zinc and nickel can only be electroplated directly on magnesium and magnesium alloys, and at the same time, it can not be used as the final coating, but only as the base of other coatings. In principle, the preparation of magnesium alloy before electroplating is similar to that of other metals. The first is cleaning to remove pollutants. Cleaning methods include steam degreasing, emulsion cleaning and alkali washing. Secondly, polishing according to the required surface smoothness, spraying glass or plastic, pickling and deburring. Before nickel plating or zinc plating, the surface of the workpiece must also be activated.
Electroless nickel plating process of magnesium alloy: traditional DOW nickel immersion method and direct electroless plating method. The former process is stable, the coating is good, and it is used a lot, but it contains chromium, which is harmful to human body and environment, so it should be used as little as possible or not. The latter process is simple, has little impact on the environment, has simple wastewater treatment and good film bonding, and has become the mainstream process of magnesium electroplating. Before nickel plating, it must be cleaned twice: first with chromic acid-nitric acid solution, then with hydrofluoric acid solution.
Usually, two chemical etchings will produce surface pitting, which provides a good mechanical anchoring point for coating deposition. After plating nickel-based coating on it, the surface of the coating is not as bright and smooth as that obtained by zinc immersion plating, but like zinc plating, this nickel plating can accept any standard electroplating, such as cadmium, zinc, copper, brass, nickel, chromium, gold, silver and rhodium. Electroless plating, such as gold or silver, can also be applied to this initial nickel plating layer.
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