Nickel Sulfamate plating on Aluminum Q&A

A. 8% silicon is not the best alloy to plate onto! In fact it is quite difficult. I do not know what you mean by "bulb" but assume the deposit has blistered. I notice you haven't mentioned a zincate treatment; this is essential in plating aluminium. Personally I do not like electroless nickel directly onto such high alloy aluminiums as there is always the risk of heavy oxides and other non-conducting things on the surface and these are often not conducive to good electroless coating. High silicon alloys need a good etch followed by a chloride-free metal eletrodeposit. This will reduce the chance of choride attacking the aluminium; you should be able to find a bromide based electrolyte from a reputable supplier.

A. First of all you need an alkaline etch prior to the HF with nitric acid.

Your electroless nickel is a home brew which is not stabilised. Why is it base on Nickel chloride?

Why 1 hour in EN? 5-10 minutes will do!

Your Nickel Chloride in the sulphamate is too high! 7 g/l will do. Nickel bromide is better.

A. Interesting article in "Plating and Surface Finishing" November 2004 about plating onto aluminium-silicon alloys. It suggests using a cleaner, followed by an etch with HNO3 and NH4HF2. It is then suggests double zincating with an etch between the two. Electroless nickel is then put down, followed by electrolytic nickel. Have a look. I agree with Sara's comments and would like to add that the pH for sulphamate nickel seems a bit low to me, try 3.7-4.5. Also, why use 8g/l nickel chloride in sulphamate? This is courting disaster as the chloride will go for any exposed aluminium. If you are not using sulfur depolarised nickel, then add nickel bromide. If you do have sulfur nickel, in theory you don't need any halogen salts, although you can still use some if you are really unhappy about not having them. The presence of chloride will certainly induce tensile stress, which could be a problem to you.

A. Ziba. I think the article in Modern Electroplating is wrong. If you use a high chloride nickel solution for plating on casting aluminum alloy, this will happen: the chloride will dissolve some alloying elements in the casting, and nickel deposit will begin to build some bridges over the pits, and some acid will stay left in the pits and lift the deposit from the aluminum. This can also happens when you over-etch aluminum.

Regards

A. Run your electrolytic nickel at about pH 3.8-4.5. If you must use a nickel halogen salt, DO NOT use chloride, but bromide. Also take note of the earlier comments above.

A. Zorivi,

To electroplate or chemical plate on Al-Si if the Si as a alloying element is too high, I prefer cleaning in a non-etching cleaner first. Etch the part for a short time in an alkaline solution only to obtain a black film on the part. This film must be removed in ammonium bifluoride acid. Rinse in water. Etch in sulfuric deoxidizer solution up to one minute. Rinse in water. Desmut in a nitric acid for a few seconds. Rinse and go to the zincate up to 30-60 seconds. Use an alkaline EN solution up to 10 micron or a neutral EN solution up to 10 micron. Or you can use an alkali copper solution as a strike. A nickel sulphate is only good enough to plate on Clean aluminum parts.

This is one and must easier method to get a uniform plating on aluminum and this alloys. To really get the best plating deposit you must let us know the other elements in the alloy.

Regards,

A. Zorivi,

The aluminum alloy from the 300 series contains a lots of Mg in the a nitric acid the Mg will be passive like magnesium nitrate and you must use a sulfuric acid to make it active to magnesium sulphate who are more easy to dissolve. I know the pretreatment steps for you are one of the problems.

Regards,

A. 400 microns is quite thick for electroplating and needs to be treated as if it was electroforming. Otherwise you may get into problems with irregular and nodular growths. I therefore suggest you use electroforming conditions for your deposit.

A. Higher filtration rates, better local current density control, more controlled deposition rates. Basically eerything you need for good electroforming. It is not just the solution you use for electroforming, its the way you do it. There are lots of textbooks around that explain in quite some detail about electroforming.

A. Dear Sir,
Chloride is too high and increase the concentration of Nickel Sulphamate to 600g/l. Use 2g/l Nickel chloride and use S Nickel as anode.