Plating on Aluminum Again

Q: Our plating shop does a lot of plating on aluminum. We always seem to have problems with blistering. When we remove some of the blisters to examine the defect, it appears that the zincate layer is at fault. Do you have any suggestions on how we can improve our zincating process? P. W.

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A: Your e-mail does not state what type of aluminum you are plating nor does it give much information on the process steps you are using. If your parts are primarily castings, the blistering is probably caused by porosity. Sadly, the porosity problem with castings has been around since “the year one.” In my experience, there is no single or complete solution to this problem. Thorough rinsing can help you to some extent. Sometimes a heavy copper plate after the zincating step can partially solve the problem.

For those of you who are not into the plating on aluminum, one of the key steps in the process is using what a zincate process step. This particular step requires taking the aluminum after it is removed from the aluminum soak cleaner and placing it in a solution that contains zinc and other metal ions. The end result is a very thin layer of zinc on the surface of the aluminum. If the zincating is done properly, you will now have the surface that can be plated.

Investigating your zincate process step will no doubt yield some worthwhile information. You did mention in your e-mail that the zincate bath you are using is a homebrew. I personally do not believe in a homebrew process baths in most situations. In the case of zincate baths this is particularly so. There are a number of commercially available zincate baths that are actually alloys made up of copper/nickel/zinc or copper/nickel/iron/zinc. Yes, these commercially available baths are more expensive than your homemade bath but they do perform better. You should also consider using a double zincate process that basically consists of zincating followed by stripping and zincating a second time.

You can find a lot of worthwhile information on the whole process of plating on aluminum by doing a search of www.pfonline.com. Another site, www.finishing.com, also has worthwhile information on the process.