1. Electroplating and electroless plating
Electroplating is to deposit a layer of other metal plating on the surface of aluminum and aluminum alloy by chemical or electrochemical methods, which can change the physical or chemical properties of the aluminum alloy surface, such as silver plating and gold plating of conductors on aluminum electronic components can improve the conductivity of their contact parts or surfaces; Copper, nickel or tin plating improves the weldability of aluminum alloys; Hot-dip tin plating or aluminum-tin alloy can improve the lubricity of aluminum alloy; Generally, chrome or nickel plating is used to improve the surface hardness and friction resistance of aluminum alloys; Chrome or nickel plating can also improve its decorative properties.
In order to solve this problem, aluminum can be deposited in an aqueous solution containing zinc compounds, and the galvanized layer is an important bridge between the aluminum and its alloy matrix and the subsequent coating.
Feng Shaobin et al. studied the application and mechanism of the galvanized layer on the aluminum matrix, and introduced the new technology and application of the galvanized impregnated process. After galvanizing and then plating, a thin porous film can also be formed on the surface of the aluminum, and then electroplated is performed.
Electroless plating refers to the film-forming technology in which a metal coating is deposited on the metal surface by an autocatalytic chemical reaction in a solution coexisting with metal salts and reducing agents, among which electroless plating Ni-P alloy is widely used.
Compared with the electroplating process, the surface treatment of zinc-aluminum alloy is a relatively low-pollution process, and the obtained Ni-P alloy is a good chromium coating. However, there are many process equipment for electroless plating, which consumes a lot of materials and takes a long time to operate.
The process is cumbersome, and the quality of the plated parts is not good. For example, according to the composition of 6063 aluminum alloy, Feng Liming et al. studied a process specification for electroless nickel-phosphorus alloy that only includes pretreatment processes such as degreasing, galvanizing and washing.
The experimental results show that the process is simple, the electroless nickel plating layer has high gloss, strong binding force, stable color, dense coating, phosphorus content between 10%-12%, and the plating hardness reaches more than 500HV, which is much higher than the anode hard oxide layer.
In addition to electroless plating of Ni-P alloy, there are other alloys, such as Ni-Co-P alloy studied by Yang Erbing et al., whose thin film has high coercivity, small remanence and excellent electromagnetic conversion characteristics, and can be used in high-density disks and other fields.
The method of electroless Ni-Co-P can obtain uniform thickness and magnetic alloy film on any matrix with complex shape, which has the advantages of economy, low consumption and convenient operation.
2. Oxidation treatment
Oxidation treatment is mainly anodic oxidation, chemical oxidation, and micro-arc oxidation. In the study of the mechanical properties and corrosion resistance of A356 aluminum alloy, Xu Lingyun et al. carried out three different surface treatments: chemical oxidation, anodic oxidation and micro-arc oxidation.
Through SEM technology, wear test and corrosion resistance test, the surface morphology, oxide thickness, friction resistance and corrosion resistance of aluminum alloy after three kinds of surface treatment were analyzed and compared in detail. The surface treatment results of zinc-aluminum alloy show that
After different surface treatments, oxide films of different thicknesses can be formed on the surface of aluminum alloys, the surface hardness and friction resistance are significantly increased, and the corrosion resistance of the alloy has also been improved to varying degrees. In terms of overall performance, micro-arc oxidation is much better than anodizing, and anodic oxidation is much better than chemical oxidation.