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Aluminum Finishing Suggestions

2006

Hello,
I am a sculpture student and am looking to have some small aluminum castings finished. I am looking for a bright finish, but am not sure where to start. I am interested in having the castings electropolished or plated, is this possible?
The parts are very complex and would be impossible to polish manually, also the alloy is 319.1 if that makes a difference.

Giles Hefferan
GVSU Student - Grand Rapids, Michigan

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First of three simultaneous responses -- 2007

You could have them Electroless nickel plated, but they will fingerprint.
I would look at finding an anodizer that has a bright dip tank which should be able to make the entire statue bright and then follow with a anodize finish and then have a real professional give it a clear coat.
Before you contract with a shop, give them some scrap metal to see if they can give you what you are looking for.This can save both of you a lot of arguments and pain.

James Watts
- Navarre, Florida

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Second of three simultaneous responses --

It is possible- but maybe expensive.Aluminum can be chemically polished too(43% phosphoric acid,10%hydrochloric acid,22% nitric acid and 25% water mixture,be careful -add acid to water never vice versa,use goggles ⇦ this on eBay or Amazon [affil links] and rubber gloves ⇦ this on eBay or Amazon [affil links] !) Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia
2007

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Third of three simultaneous responses --

Giles,
There are electropolishing solutions for Al alloys and zincating processes for Al to plate a variety of metals. If it is affordable to you, bring the parts to a plating shop and tell them what you want. It is not advisable that you try to accomplish this in the home. Good Luck!

Mark Baker
Process Engineer - Syracuse, New York
2007

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2007

Giles,
The alloy matters. For bright anodizing (chemical or electropolishing, + anodizing), use a relatively pure Al-Mg alloy such as 514.2 (Al-4%Mg-max 2% others) rather than 319.1 (Al-3.5Cu-Fe-6Si-2% others). Casting Kaiser Aluminum, 3rd Edn., describes mechanical and anodized finishes on 319 as only fair [with yellow from the Cu & gray from the Si, I expect brownish anodize], while 514 "takes an excellent polished finish" and "Anodized appearance and protection are excellent."

Also, the Al-Mg-7Zn alloys 771.0 & 771.2 polish to "a fine chrome-white finish...anodizes to a satin white finish and dyes brilliantly...retain the chrome-white color under corrosive conditions, an advantage for architectural and ornamental castings that are exposed to the atmosphere."

If mechanical polishing is too difficult and chemical or electropolishing processes are unavailable in your area, try lightly glass bead blasting.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.