In the electroplating industry, zinc replacement liquid is an important part of the pre-plating treatment of aluminum and its alloys. Although aluminum is widely used for its lightweight and high-strength properties, when it comes to plating other metal layers on its surface, it must first overcome its naturally formed oxide film and low surface activity. This is because the oxide layer significantly reduces the adhesion of the metal layer. The application of zinc replacement liquid is the key to enhance this adhesion.
The zinc replacement liquid consists mainly of a zinc salt (such as zinc chloride), a base (usually sodium hydroxide), and some potential additives such as complex agents and surfactants. Through a carefully designed chemical reaction, the solution forms a thin zinc film on the surface of the aluminum. This process is actually a displacement reaction, in which active zinc ions replace a part of the aluminum surface, thus forming a layer of zinc on the aluminum surface.
The existence of this newly cast zinc film is crucial for the subsequent electroplating process. There are three reasons:
1. Provides a good adhesion base: zinc and many electroplated metals, such as nickel, copper, chromium, etc., are easier to form a strong chemical bond than aluminum. Therefore, the zinc layer becomes a kind of "intermediate layer" between the metal coating and the aluminum substrate, which improves the bonding between the metal coating and the aluminum substrate.
2. Improve the surface roughness: the surface of the aluminum surface formed after zinc replacement is rougher than the original smooth aluminum surface. This slight increase in surface roughness provides more anchorage points and further improves the mechanical adhesion of the coating.
3. Prevent oxidation layer regeneration: Because aluminum is easily regenerated in the air, the existence of the zincized layer can isolate the direct contact between aluminum and air to a certain extent, slow down the oxidation process, and provide a more stable window period for electroplating.
However, the quality of zinc replacement layer depends on the ratio of zinc replacement solution, PH value, temperature and treatment time. Once the operation is poor, the result can be holes in the coating, stripping and other problems with poor bonding. Therefore, Bigley's zinc replacement liquid is needed when aluminum plating is used for zinc deposition.
If you are interested in zinc replacement liquid, please feel free to contact us.
