Preparation method of magnesium alloy surface metal plating layer

Abstract

The invention relates to a preparation method of a magnesium alloy surface metal plating layer, which belongs to the technical field of metal corrosion and protection. The method comprises the following steps: (1) carrying out preliminary treatment on the surface of the magnesium alloy; (2) carrying out advanced chemical nickel plating on the surface of the magnesium alloy after the preliminary treatment, wherein an advanced chemical nickel solution is prepared from 15 to 30 g / L of nickel hypophosphite, 5 to 20 g / L of sodium hypophosphite, 8 to 30 g / L of organic coordination agents, 10 to 50 g / L of inorganic coordination agents, 3 to 5 g / L of glycin, 5 to 15 g / L of ammonium hydrogen fluoride, 5 to 10 g / L of sodium acetate, 3 to 5 ppm of potash iodate and 10 to 30 mg / L of dodecyl sodium sulfate, the temperature of the advanced chemical nickel plating is between 50 and 70 DEG C, the pH value is between 7 and 10, and the time is between 30 and 120 min; and (3) carrying out thickening chemical nickel plating or plating other metals on the surface of the magnesium alloy after the advanced chemical nickel plating. The method of the invention improves the combining force of an advanced plating layer and a magnesium alloy base body, and reaches the national standard after the addition of a proper amount of pyrophosphate complexing aids. Metal decorative protective plating layers with strong combining force and high corrosion performance can be obtained after further conventional nickel plating or other metal plating on the advanced chemical nickel plating layer.

Description

Technical field [0001] The invention belongs to the technical field of metal corrosion and protection, and particularly relates to a method for preparing a metal coating on the surface of a magnesium alloy. Background technique [0002] Magnesium alloys have excellent properties and are increasingly widely used in the fields of automobiles, machinery, aerospace, and portable electronic instruments, computers, hand tools and camera parts. However, since the electrode potential of magnesium alloy is relatively negative (the standard electrode potential of magnesium is E 0 =-2.36v), the chemical activity is extremely high, and it will suffer severe electrochemical corrosion in humid air, sulfur-containing atmosphere and marine atmosphere. This prevents magnesium alloy products from exerting their advantages in applications and limits their application scope. So generally take surface protection treatment measures to improve its application performance. At present, more paint coati...

AI Technical Summary

Problems solved by technology

Using zinc-copper cyanide primer method is the earliest process for magnesium alloy to obtain metal coating, but the process is complicated and seriously polluted; recently, American experts and scholars have proposed that direct copper immersion on magnesium alloy (Luanetal, US Patent, 6669997B2) Or immersion zinc (Pearsonetal, US Patent, 0039829A1) instead of immersion zinc-copper cyanide process, although no cyanide is used, the bonding force between the copper layer and the substrate obtained is not ideal; and basic nickel carbonate is used as the main salt electroless nickel plating , although avoiding the use of nickel sulfate and nickel chloride salts to bring SO 4 2- , Cl - The disadvantages of accelerated corrosion of the base magnesium alloy, but the use of basic nickel carbonate needs to be dissolved with HF acid, the pollution is large and the cost is high, and the process is not very stable, especially for the treatment of AZ91D magnesium alloy die castings.

Recently, as China's patent application "magnesium alloy nickel sulfate main salt solution and its electroless plating process" (publication number CN1598053A), "method for electroless nickel-phosphorus alloy plating on the surface of magnesium alloy" (publication number CN101275221A), and "with nickel sulfate The Surface Electroless Ni-P Plating Process of the Main Salt" (public number CN101187020A) all introduces the use of nickel sulfate as the main salt to reduce costs, but in the chemical nickel plating formula, a higher concentration of fluoride is used as a corrosion inhibitor, and in Higher concentration of hydrofluoric acid is used in the pre-treatment pickling and activation stages, so the pollution is more serious, and the process is still not very stable, especially the bonding force of the coating is not good, and the treatment of AZ91D magnesium alloy die castings is not mature enough