Metal finishing Q&As since 1989

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Gold plating of aluminum advice needed

March 7, 2008

I am just about to plate Aluminium for the first time. I am quite efficient in decorative plating SS but my stores needs have changed. I have a lot of money invested in this and need good results fast.
I would appreciated it if someone would just double check to make sure I am going to be doing this right.
1st Bead blast the Aluminium
2nd Dip in Zincate until dark grey colour
3rd Clean well with water
4th dip in nitric acid 15-20 sec's
5th Dip into zincate
6th Wash with water
7th E.N plate
8th Activate
9th Proceed with gold plating

Is that correct? Also could someone tell me if after zincating the part is it possible to selective plate or does it have to be done in a tank. Reason I am asking is I do have some small parts and it would make life a lot easier.
Thank you,

Davie Scott
Plating shop employee, Store owner - Glasgow, Scotland

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Hi Davie,
First we most know the aluminium alloy to get you a answer on your question.
Second to activate a electroless nickel is a problem, because phosphorus. The pretreatments step you describe is not the right steps, but maybe you can get adhesion.

Regards

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
March 27, 2008

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First of two simultaneous responses --

I think that you are in step 2 --too long.
Step 4 time depends on the concentration of the nitric and it's "use age".
Go immediately from the EN to the rinse and immediately into the gold.
It would be my preference to use an Alkaline EN strike followed by EN if you need the build up and then gold.
Activation of EN is problematic. Big time.

James Watts
- Navarre, Florida
March 27, 2008

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Second of two simultaneous responses --

Assuming you are not doing cast aluminum, your process is standard. But here are some ways to improve. Be sure the beads are designated aluminum-only and that we are not pounding any iron or brass into the soft Kleenex-like aluminum surface. You may be able to use only a single zincate, but make the final one as light as possible, like 30 to 45 seconds. Rinse off the zincate in 4 oz/gal sodium carbonate. Strike in ALKALINE electroless nickel, then plate anything you want to.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

March 27, 2008