One-step acid washing activating plating pre-processing technique for magnesium alloy surface

Abstract

The pickling and activating surface treatment process for magnesium alloy workpiece before electroplating is one simplified environment friendly process including the surface treating steps of alkaline washing, pickling and activating, and zinc dipping. In the pickling and activating step, the pickling and activating solution including sodium phosphate in 22-65 g/cu dm, phosphoric acid in 31-86 g/cu dm, and potassium permanganate in 10-30 g/cu dm is adopted. The present invention features the combined pickling and activating step, the pickling and activating solution without harmful chromium compound and fluoride, the obtained zinc dipping layer with homogeneous and compact structure suitable for electroplating and chemical plating, and capacity of reaching excellent coating.

Description

technical field [0001] The invention belongs to the field of metal corrosion and protection, and in particular relates to a surface treatment method before one-step pickling and activation electroplating or electroless plating of magnesium alloys. Background technique [0002] Magnesium alloy is known as the green metal structural material in the 21st century. It has low density, high specific strength and specific stiffness, and excellent damping, machinability, and casting performance. It has been increasingly widely used in the automotive industry, aerospace industry, and electronics industry. application. Magnesium is rich in raw materials and ranks eighth among natural resources, but as a structural material, its poor corrosion resistance restricts its wider use. [0003] The standard electrode potential of magnesium is -2.34V, which has high reactivity. In air or solution, magnesium alloy will quickly form a very thin passivation film, which will lead to the metal coa...

AI Technical Summary

Problems solved by technology

Most of these pretreatment processes include four main steps: degreasing, pickling, activation, and zinc immersion. The process is relatively cumbersome and complicated. The plating solution contains highly toxic cyanide, and the waste liquid treatment costs are high.

[0005] In order to overcome the disadvantages of complex process, researchers have developed a direct electroless nickel plating method, such as Mizunari [4] In the invention patent JP Pat, 2003073843, chromic anhydride is used to etch the magnesium alloy, and the electroless nickel plating is performed after the fluoride is activated. The electroless nickel plating solution is adjusted with ammonia water to make it weakly alkaline, and good bonding force and corrosion resistance have been obtained. Highly resistant electroless nickel layer, Li Degao [5] etc. In the patent CN 1699634A, a magnesium alloy electroplating method adopts deflocculation → chemical degreasing → light emission → neutralization → activation → pre-galvanizing process to obtain a better pre-galvanized layer, and the pre-galvanized liquid is cyanide-free and non-toxic. poisonous, harmless, Yang Yi [6] In the patent CN 1737205A, the magnesium alloy is directly electroplated with aluminum after pickling with concentrated hydrofluoric acid (11%) to obtain a relatively good aluminum coating. Chinese patent [7] CN1641075A has done a detailed description of the surface or activation treatment method and surface plating method of magnesium and magnesium alloys. Although these processes have all broken away from cyanide electroplating, the treatment process before electroplating is mostly based on the improvement of the DOW process, pickling and activation The solution contains chromium ions and fluoride ions that are harmful to the human body and the environment. For this reason, Li Yuanfa [8] In the patent CN 1584127, a new magnesium alloy surface activation process was invented, but no specific electroplating example was found. In addition, the activation process was complex and included three steps: mechanical roughening, electrolytic degreasing, and chemical activation solution activation. The coarsening step requires a special grinding fluid to increase the processing difficulty, and the electrolytic degreasing increases the production cost

Zhou Wanqiu [9] People such as patent CN 1084145A in the method for zinc plating on magnesium alloy directly carry out galvanization with the pretreatment process of chromium-free alkali etching after hydrofluoric acid activation, obtain better galvanized layer, but still use in this activation process A large amount of highly toxic hydrofluoric acid