Zincate formulas for plating on aluminum

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

on eBay or

AbeBooks

or Amazon

(affil links)

A. Hi Nash Shafique.
2nd question first because it's important; you shouldn't use flammable materials like kerosene to do the cleaning! The generally accepted way to clean aluminum is with a non-etching alkaline cleaner (with ultrasonic agitation added if it helps with the particular parts). If you can't buy a proprietary, and don't want to spend a great deal of time in research about inhibitors, you can see how a mild sodium hydroxide [affil links] mixture works, but you must limit the immersion time.

Wernick, Pinner & Sheasby suggests that 23 g/l sodium carbonate ⇦this on eBay or Amazon] and 23 g/l of trisodium phosphate ⇦this on eBay or Amazon [affil links] operated at 60-80 °C might be an adequate cleaner ⇨

Regarding the first question, yes 40-50 g/l zinc oxide ⇦this on eBay or Amazon [affil links] and 400-450 g/l sodium hydroxide [affil links] can be used. Ramanan Natarajan, in the earliest post in this thread apparently feels it can be improved by adding ferric chloride and Rochelle Salt ⇦this on eBay or Amazon [affil links] , and it seems that Wernick, Pinner & Sheasby ⇨
feel it's an improvement -- but only one of numerous possible ones ⇨
Ghulam Fareed offers a formulation further down this page.

If a library near you can get you the book I've been quoting, it's over 1200 pages and covers such subjects exhaustively.

We've certainly said this before, but please do your best to test each individual step before committing to it :-)
Luck & Regards,


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

A. Hi Saed,
In brief: non-etch cleaning, etching, desmutting, zincating, a 1st layer of plating compatible with zincate, and final layers of plating.
Luck & Regards,


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

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

on eBay or

AbeBooks

or Amazon

(affil links)

A. Hi Ramanan, hi Adarsh.

I am not experienced in zincating of evaporated thin films, but zincating of aluminum as a preparatory step to electroplating on aluminum is a very popular and mature industrial process, at least for large parts. Thousands of miles of aluminum bus bar has been zincated then copper plated; hundreds of thousands (maybe millions) of aluminum automobile and truck bumpers have been zincated then copper-nickel-chrome plated; tens of millions of aluminum die castings and electronic parts have been zincated then plated.

So a lot of research has been done. Here are some good papers by David Lashmore that focus on what is happening at the molecular level, and which may be helpful to your studies:

• "Immersion Deposit Pretreatments for Electroplating on Aluminium - Literature Review", Plating & Surface Finishing, Apr. 78.
• "Progress in Plating onto Aluminium", Plating & Surface Finishing, Jan 80.
• "Plating on Aluminium - A Review", Plating & Surface Finishing, June 85.

General conclusions seem to include the observations that:
- Proprietary mixed metal zincates (such as Macdermid/Canning/Gumm's Bondal) really do work better, and
-The common procedure of zincating followed by stripping with nitric acid and re-zincating (commonly called double zincating) is essential to a fine grained deposit on some types of aluminum.

As for pretreatment, the same steps used for anodizing and chromate conversion coating (clean, etch, de-smut) are fine. Your evaporated films may, of course, not sustain the robust pretreatment used in industrial electroplating onto aluminum.

A. The use of zincate is well established as an adhesion layer for Al. Developed a process for plating Ni and Au on very thin films of Al on power devices using zincate as an activation layer. It was a technology used to fabricate flip chips

A. Yes, that formulation doesn't have much to recommend it, except that it won't violate any patents, and you did not have to ply a formulator with strong drink to get it:-0

Die castings will take an uneven zincate, due to the exposed grain structure, but you might want to try degreasing the part with an alkaline cleaner and aluminium etch for your next experiments. A blotchy zincate could mean that the part was dirty with grease or oil too.

Proprietary formulas will do a much better job.

A. As Tom mentioned, your preplating process is not good enough. You need to degrease, etch and desmut before the zincate. Using only Hydroxide with zinc oxide will give you an unstable zincate layer. (By the way, you have to use a double zincate). A proprietary zincate will be far better.

A. Zincate is best double-dipped but not necessary. We have a great zincate that uses a combo of zinc, copper, nickel and iron. The advantage of so many complexes is that they can attach to different sites on the alloy. 5 to 1 ratio is best for your zinc to hydroxide formulation, but try to add 10% sodium cyanide, 5% nickel carbonate, 3% ferric chloride, 6% copper cyanide. That's the best the industry can offer and is very forgiving in its nature.

Regards and good luck

sandra

A. Hi, Renar.

We can't say when or if Sandra will return to clarify her response, but the Metal Finishing Guidebook offers this (strong) formulation: NaOH 67 oz./gal
ZnO 13 oz./gal
FeCl.6H20 0.3 oz./gal.
Sodium Potassium Tartrate ⇦this on eBay or Amazon [affil links] 1.3 oz. gal

So, combining this information with Sandra's, one way of following her suggestions would seem to be approximately:

NaOH 67 oz./gal
ZnO 13 oz./gal
FeCl.6H20 0.3 oz./gal.
NaCN 1.3 oz./gal
NiCO3 .6 oz./gal
CuCN 0.6 oz./gal

Please note that this is a very strong formulation, and it should be possible to very significantly reduce the NaOH and the ZnO as long as they are reduced proportionately, maintaining roughly a 5 to 1 ratio. Also note that this formulation includes cyanide and should not be used unless you are already familiar with cyanide-based processes and their dangers.

Regards,

A. There are many different formulations that can be used to make-up a zincate solution. The two you have are good and there are many others depending on what alloy you are using and what you would like your adhesion to be like. You can get the various recipes from literature, books and the internet.

A. 1 - 245,100 L AGUA [water]
2 - 005,400 KG GLUCONATO DE SODIO [sodium gluconate] (DISSOLVINE NG C)
3 - 004,200 KG CLORETO FERRICO [ferric chloride ⇦this on eBay or Amazon [affil links] ]
4 - 138,000 KG SODA CAUSTICA [caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] ] 99 / 98 % RAYON GRADE S/ CARB
5 - 020,400 KG OXIDO DE ZINCO [zinc oxide]
6 - 006,900 KG ACIDO SALICILICO [salicilic acid]

A. To call it a cyanide zincate is probably a bit of an overstatement. A zincate or alloy zincate that contains a trace amount of cyanide would be a much fairer answer. When I was actively in plating, I never came across a plater that did not say that it had better adhesion. Harder to control and it does require special haz waste procedures for that tank and rinses. Not all that difficult. Very few platers use it because a normal double zincate will suffice for nearly all work.

A. Yes cyanide zincate is used. I think there are non-cyanide zincates that have been developed. I don't know what process you use other than zincate and nitric acid to strip before copper strike/electroless nickel strike.

A. Hi Pari. We appended your inquiry to an earlier thread. Please see above, which will refer you to some excellent investigations about zincating. Good luck. Regards,

Yes, old issues of P&SF can be hard to find at present, Ken, which greatly limits the value of my answer. But per the exec director's report at Sur/Fin, AESF is planning to put their old issues on line.

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

A. Formulation of zincate:

Sodium Hydroxide 400-500 gm/l
Sodium Cyanide 5-7 gm/l
Zinc Oxide 20 gm/l
Rochelle Salt 50 gm/l
Sodium Nitrate 1 gm/l
ferric chloride 2 gm/l
copper sulphate ⇦this on eBay or Amazon [affil links] 10-15 gm/l

A. Proprietary zincate solution are usually considered better, and the technical support may be useful. For do-it-yourself solutions, see ASTM B253, 'Standard Guide for Preparation of Aluminum Alloys for Electroplating.'

A.
1. You do not need "tri-acid" for the wrought alloys you listed, just use plain nitric acid without the ABF.
2. Select a "dilute" zincate from any reputable supplier.
3. My experience has found no reason for double zincate.
4. Strike first in an alkaline electroless nickel, then rinse, dip in ammonia ⇦this on eBay or Amazon [affil links] rinse and go on into the acid electroless nickel. The expensive acid EN will last longer by not "seeing" the zinc, and the alkaline EN has far more tolerance for the zinc.

A. Hi Dale. We appended your inquiry to a thread which addresses most of your inquiry, except that the previous posters seemed more interested in zincate as an immersion pretreatment for aluminum rather than as a plating solution. Are you trying to make acid, cyanide, or alkaline non-cyanide plating solution? Are you a hobbyist or are you an experienced zinc plater and this is for production use?

Luck & Regards,

A. Hi Muhtar. Numerous formulas are on this page we appended your question to, along with suggestions that proprietary zincates will probably outperform them. Good luck.

Regards,

A. Old zincate formula according to Hewitson patent (1926.) -
1,000 water,
50 parts of zinc chloride,
150 parts of sodium hydroxide, and
40 parts of sodium silicate solution.

Hope it helps and good luck!