1. Electroplating and electroless plating
Electroplating is to deposit a layer of other metal coatings on the surface of aluminum and aluminum alloys by chemical or electrochemical methods, which can change the physical or chemical properties of the surface of aluminum alloys, 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; while 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 also improves its decorative properties.
In order to solve this problem, aluminum can be deposited in an aqueous solution containing zinc compounds, and the zinc immersion layer is an important bridge to connect aluminum and its alloy matrix and subsequent coating.
After galvanization, electroplating can also form a thin porous film on the surface of aluminum, and then electroplating.
Electroless plating refers to the film formation technology of depositing metal coating on the metal surface by autocatalytic chemical reaction in a solution coexisting with metal salts and reducing agents, among which electroless plating Ni-P alloy is widely used.
Zinc and aluminum alloy surface treatment Compared with the electroplating process, electroless plating is a relatively low-pollution process, and the obtained Ni-P alloy is a good subsistence for chromium plating. However, there are many process equipment for electroless plating, large material consumption, long operation time,
cumbersome process, and the quality of the plating parts is not good. For example, Feng Liming et al. studied a process specification for electroless nickel plating phosphorus alloy that only includes pretreatment processes such as degreasing, zinc dipping and washing according to the composition of 6063 aluminum alloy.
The experimental results show that the process is simple, the electroless nickel plating layer has high gloss, strong bonding, stable color, dense coating, phosphorus content between 10%-12%, and the hardness of the plating state reaches more than 500HV, which is much higher than that of the anode hard oxide layer.
In addition to electroless Ni-P alloy, there are other alloys, such as Ni-Co-P alloy studied by Yang Erbing and others, whose thin films have high coercivity, small remanence and excellent electromagnetic conversion characteristics, and can be used in high-density disks and other fields
The method of electroless plating of Ni-Co-P can obtain uniform thickness and magnetic alloy films on any complex shaped substrate, which has the advantages of economy, low consumption and easy operation.
2. Oxidation treatment
Oxidation treatment is mainly anodizing, chemical oxidation, and micro-arc oxidation. Xu Lingyun et al. conducted three different surface treatments on A356 aluminum alloy: chemical oxidation, anodizing and micro-arc oxidation.
Through SEM technology, wear test and corrosion resistance test, the surface morphology, oxide layer thickness, friction resistance and corrosion resistance of aluminum alloy after three surface treatments were analyzed and compared in detail. The surface treatment results of zinc-aluminum alloy show that
the surface of aluminum alloy can form oxide films of different thicknesses after different surface treatments, the surface hardness and friction resistance are significantly increased, and the corrosion resistance of the alloy is also improved to varying degrees. In terms of overall performance, micro-arc oxidation is much better than anodizing, and anodizing is much better than chemical oxidation.