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Zinc Phosphate and Protecting Aluminum

How well does zinc phosphate protect aluminum?
We have an aluminum product (bezel) that has been powder coated on one side (users side). The side to the interior of the box is not powder coated. Up until recently, Alodine process has been used to protect the aluminum.
It has been suggested to us to use zinc phosphate as that is friendlier to the environment. According to a google search and letter no. 1070, zinc phosphate may not give a good corrosion protection. Depending on the thickness or weight.
Our instruments are mounted on helicopters. Some users are near the ocean or gulf.
Another question - what measurement system is there for zinc phosphate?

Matt Sample
electronics - Pensacola, Florida, USA
2006

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First of two simultaneous responses --

Not very good. It is ok as a paint base, but not much good as a stand alone. One major problem with it is that you can not do a visual check as it looks like a bad etch rather than a color like the chromate you are used to.
search the site for (Navy's new) trivalent chromium chromate. Avoids hexavalent and the Navy is satisfied with it.

James Watts
- Navarre, Florida
2006

Ed. note: The four current licensees of this Navy TCP process are CST-Surtec, Henkel, Luster-On, and Metalast.

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Second of two simultaneous responses -- 2006

Matt,

Are you the design authority for the part? If not STOP! Any changes to the design has to be authorised by the design authority. If you make changes without the design authority say-so you incur the wrath of both your customer and the FAA.

If you are the design authority you could consider trivalent chromate conversion. The performance, as I understand it, is not quite as good but it may well be good enough for what your looking for.

If you were to use zinc phosphate (zincate is another way you will hear it described) then you need to use a supplementary treatment such as a lacquer or a paint primer. These will greatly increase the corrosion resistance of the part.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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2006

Thanks for the response describing the trivalent chromate. We will investigate this process.

Brian - I appreciate your concern about design authority. A person or company does need to remember that part of this business. Therefore, I assure you, that is in the process - as every other "T" to cross and "I" to dot is being considered.

Again, to all, thanks for possible solutions.

Matt Sample
Electronics - Pensacola, Florida, USA

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There are processes available in India & US which are meant for Aluminum specifically. These products are totally (100%) Chrome free. You can freely search for such products on the www.

Regards,

Anurag Kanaujia
- New Delhi
2006