Passivation on Electroless Nickel Plating

According to MIL-C-26074E Coatings, Electroless Nickel. The minimum coating for aluminum alloys is 26 Microns (0.026 mm). This specification doesn't require any passivation but only various heat teatments for various uses such as improved adehesion etc.

I know MIL-C2607E specification for electroless nickel plating I have work on it many years ago. As far as I know there is no need to a passivation for nickel plating. We were using very low concentration of chromic acid for to keep the color of nickel plating lasts long and do not darken. For adhesion, only factor is to make the pretreatment of the main metal very well. Any fault in pretreatment causes problem that hardly can be recure. Most important part is to control the phosphate content of the cauting. All the characteristics of the eletroless nickel cauting depends to nickel/phosphate ration. As far as I can remember, Specification gives only the hardness of the electroless nickel. Heat treatment can give that hardness depending the phosphate ratio. You need to contact with your elecroless couting chemical supplier for more information because there are many different methods and chemical compositions that electro plating chemical manufacturers. I was using German Compschoulte process( I think they are no more avaible) and passed the tests without any difficulties.

Hope my old experiances can halp a little.

Regards

i always thought that passivation was strictly used on Stainless Steel.

http://www.electrohio.com/Finishing/Passivation/Passivation.htm

Passivation improves the corrosion resistance properties of components made of precipitation-hardened, austenitic, ferritic and martensitic steels. Passivation treatments improve the surface condition of stainless steel by dissolving iron that has been imbedded in the surface during forming or machining. If allowed to remain, the iron can corrode and give the appearance of rust spots on the stainless steel.

Passivation, which consists of immersing stainless steel components in a solution of nitric or citric acid without oxidizing salts, will dissolve the imbedded iron and restore the original corrosion-resistant surface by forming a thin, transparent oxide film.

Aluminum is also passivated. The purpose is to promote a thin (passive) film of aluminum oxide to help protect the surface of the metal. I can't remember the last time I saw a callout for this.

Most of our aluminum work is anodized.

I dunno?

We may be talking semantics, but i don't think I've ever heard/seen of Aluminum being "Passivated" .

Besides Anodize, Iridite is commen (although that word in itself is a brand name that belongs to MacDermid Inc for a chromate coating) as a protectant against oxidation for aluminum alloys.

Anodizing is an electrical insulator while iridite is not.

I am using chromic acid to passivate the Nickel surface that can prevent the surface change yellowish or darken after long storage time. At the same time, I have problem with the environmental regulation and my waste water treatment system is not capable to treat the Cr6. Do you have any better option for the same application?

As advised on a previous post, 5-8 microns is insufficient to protect porous cast aluminum. Even 26 microns will not even begin to protect against any standard salt spray test. Depending on the severity, you will need at least 100 microns and probably 200-300. Reactivate the nickel and add more (if you can allow the increased/decreased dimensions on the part). Plating suppliers often require 50-100% margin on the plating thickness, so contact one first before specifying your finish.

Good Luck!

Dear Tom,

As my friends mentioned before, passivation of nickel electroless or electro plating has no affect to corrotion. Nckel plating usually have low corrition resistance. This is why we usually prefer a cupper plating under Nickel plating. For electroless nickel as far as I know corrotion resistance depends mostly to the Nickel/ p2o5 ratio. As the p2o5 content increases corrtion resistance and hardness increases also. As my friens says 5-8 micron is not enough for any corrotion resistance unless there is a thick cupper plating under it. You can sellect eaither electroless cupper or electrolitik cupper for to get a better salt spray. I think, 5-8 micron electrless nickel has no affect to any of the benefit of electroless nickel plating, it can only makes a hard and decorative plating and would let you use some additives like teflon to decrease friction coefficient of the surface. I was plating the center of the clucks with additive of teflon to decrease and the wearing of the opposite working part by adding teflon to electroless nickel.

It was long time ago, please correct if I have any mistakes. You should contact with your electroless nickel plating chemical supplier for the additives and rest of the specifications. There are many different methods for elecroless nickel so it changes which method you sellect for to control the plating composition.