Plating On 356 Aluminum Alloy

Q: We are having a difficult time plating on a casting made from 356 aluminum alloy. Blistering and peeling are a constant problem. We are double zincating using an in-house formulation. The process use works well on other aluminum alloys. Do you have any suggestions as to how we can solve our problem? L. M.

A: Aluminum alloy 356 is sensitive to the preparation cycle prior to plating. One of the things that comes to mind is that your zincate may be too heavy for this particular base material. There are two things I would suggest: One is to operate your zincate bath at a temperature of 60–65°F, and the second is to get rid of your “homebrew” zincate solution and start using one of the proprietary ternary alloy zincates. Proprietary zincates are available from a number of different suppliers. Vendors of ternary alloy zincates can be found in the supplier database on http://www.pfonline.com/ or in the PRODUCTS FINISHING DIRECTORY AND TECHNOLOGY GUIDE.

You should also evaluate your rinse cycles between the various steps in your process.