Zincating on Aluminum: Problems with 6000 series

A. Use 30% Nitric Acid instead of HF and Sulfuric Acid.

The way you are racking, if there is any floating soil on the rinses, you will pick it up and re-deposit something that will interfere with adhesion.

An alternate idea that would skip the nickel strike. Use a proprietary alkaline zinc plating solution, put the aluminum in and wait 30 seconds before slowly and lowly turning on the current, zincate will start then gradually turn up the current and you can build up enough zinc to support the addition of tin.

A. The main problem with zincating aluminum for pre-plating purposes is that aluminum forms an oxide extremely quickly which hampers plating. Typically, I have never had good results with a single zincate cycle. I would suggest a double zincate which allows for a finer deposited zincate, and more sites for subsequent adhesion. Also, to be noted is that do not, repeat do not allow the parts to become dry at anytime. As you can gather, any staging in rinses through-out the pre-plating cycle, or any delay in the pre-plating cycle can allow aluminum oxide formation. Further, any delay in the plating cycle up to whatever your strike is will cause you problems. The other issue with aluminum finishing of any kind is the cleaning cycle, which is undoubtedly the most neglected part of any aluminum finishing, especially if one is a plater and not an anodizer. An excellent resource would be to contact the manufacturers of zincate products as they will have recommended zincate and cleaning cycles for aluminum.Be sure to let them know what your zincate formulation is, as some zincate formulations are to be used for different types of plating, such as electrolytic nickel, vs copper, vs electroless nickel vs copper, etc.

A. There should not be a noticeable difference between the tempers, however your problem is most likely due to the alloying constituents. Alloys which are more difficult to zincate such as higher silicon containing alloys definitely require a double zincate. Also, depending upon the alloy types one needs to use different acid etching or pickling solutiuons. One good one for high silicon containing alloys is a 75%Nitric/25%hydrofluoric acid etch.This is a dangerous solution to work with and needs special first aid treatments to be available. Another solution which is not as dangerous is an Ammonium Bifluoride/Nitric acid solution as described in the Metal Finishing Guidebook. That solution is used prior to your first zincate, use a 50% nitric Acid to remove the first zincate and then re-zincate. That should fix your problem. You are starting to ask questions which require more than a simple email response. My suggestion would be to access the available literature and get a hold of your zincate solution supplier.

A. Try going in "live" in the tank, it took care of my problems.