How can aluminum be coated?
As soon as uncoated aluminum comes into contact with oxygen, an oxidation process begins. However, this process hinders the coating. Therefore, aluminum workpieces always require pretreatment with an aluminum activator. This removes the oxide layer and, in the same process, creates a zinc layer on the surface of the material. In this way, the activator prevents contact with oxygen and protects against renewed oxidation. To reliably prevent the formation of bubbles under the coating, we offer our customers an aluminum activator with a low viscosity.
However, zinc is not acid-resistant. Therefore, in the next step, you apply a layer of alkaline/basic copper and then a layer of acidic copper plating solution. This creates a stable base for any further layers.
Depending on the aluminum alloy, it may be necessary to etch the surface in the first step before applying the zinc layer with the aluminum activator. The applied zinc layer is etched again and the treatment with the activator is repeated a second time. This is done because the zincate layer becomes relatively rough and the pores close better. Unfortunately, the zincate process can be considered complicated.
The following sequence would therefore be required to chrome or gold plate aluminum:
- Conditioner for etching
- Aluminum activator to create the zincate layer
- Alkaline copper plating solution to obtain an acid-protective copper layer
- Glossy copper plating solution (acidic)
- Nickel plating solution (Free-Nickel), as a diffusion barrier
- Chrome plating solution or gold plating solution as a final layer
