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Electroplating onto Aluminum

I am looking for a process to electroplate Al to create a solderable surface. I have tried using Ag, Au, and some silicates. It seems that Ni is the best element to use, but the Ni forms spheres and does not adhere to the surface. Is there a method for preparing the surface before the electroplating? Also, are there any better methods to use to electroplate the Al?

Brian M [surname deleted for privacy by Editor]
- State College, Pennsylvania ,USA
2000

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Hi, Brian. Try looking up 'zincate', or its proprietary alternatives like 'Bondal' or 'Alstan'. You must form an immersion deposit of zinc or tin on aluminum before you can proceed with the rest of the plating steps.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000

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As Ted says, you need an immersion deposit of zinc or tin on the aluminium surface. The easiest method is the zincate process, which can be a one or two step process. This is well documented in most good plating books and most supply houses have a suitable system.

There is, however, one other thing to consider, that of the type of alloy being plated. High alloy aluminums are not as easy to deposit metal onto as low alloy systems. The key to successful metal adhesion is good wetting and cleaning. If the wrong cleaner system is used with high alloy aluminums there is a tendency to form smuts that need to be removed before the zincate treatment. Check on your alloy and then talk to your supply house about the best cleaning process. I would suggest a cleaning system that uses both an alkaline etch and an acid clean. The acid usually removes the smut, but you need to ensure it is suitable for the alloy. One of the most common acid treatments is based on nitric acid and hydrofluoric acid, but HF is really nasty and if possible should be avoided. There are some acid cleaning systems around that are based on sulfuric acid, but the exact conditions may vary with the alloy.

One more tip, try to avoid high silicon alloys as whilst they can be electrochemically coated with another metal, they are real pigs to clean and condition to accept a really adherent deposit.

Any supply house that has a zincate system on its books will also have a bespoke cleaning system; - if it doesn't, look for another supplier!

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2000