finishing.com -- The Home Page of the Finishing Industry

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
The world's most popular metal finishing site, and striving to be the internet's friendliest corner

topic 17772

Anodizing polished aluminum


A discussion started in 2002 but continuing through 2019

2002

Q. I have a need for anodizing a near-mirror polished aluminum (6061) part without degrading the polish, or say, with minimum degradation. The surface needs to be electrically non-conductive, and the depth of anodizing to be at least a few microns (> 0.0001"). Is it possible?

Mandar Sunthankar
- Fort Collins, Colorado


"Surface Treatment & Finishing of Aluminium and Its Alloys"
by Wernick, Pinner & Sheasby
from Abe Books
or
info on Amazon

2002

A. Your anodizing thickness is on the thin side for corrosion resistance, but it could be alright if the potential for corrosion isn't bad. Millions upon millions of reflectors for internal use (dentist lights, indirect lighting sconces) and external use (highway and city lighting) have been built of aluminum. Although 6061 is a good alloy for anodizing, the purer alloys would give a purer (and thus more transparent and smoother) anodized coating.

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


2002

A. Yes, it is possible...although the silicon content in 6061 may cause you to lose some of your mirror finish. If I were you, I'd change your alloy to one with less Si (5052 comes to mind). And, obviously, keep your coating thickness to the bare minimum. Another option would be to electropolish the Al just prior to anodizing (but again, the 5000 series of Al is more conducive to EP than the 6000 series).

Marc Green
Marc Green
anodizer - Boise, Idaho


2002

Q. Ted and Marc, thanks for the info. Is there a particular name to this process (hard, clear) or specific chemical (chromic, sulphuric), any temperature, etc., as general info to get it done from an anodizing shop ? Is this a specialty process or most anodizing shops could do it ?

Mandar Sunthankar
- Fort Collins, Colorado

2002

A. "Clear" is an okay description, Mandar; "sulfuric acid anodizing" is fine too; or "Type 2"." Yes, virtually any anodizing shop will be able to do the anodizing.

But if you decide that a chemical "bright dip" is appropriate after your mechanical polishing--or an electrolytic polishing as Marc mentioned--then you will find that many anodizing shops lack that capability.

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


2002

A. In regards to the topic of material choices. What is this part shaped like? Is it a solid block of billet 6061? Is it plate or sheet? The reason I'm asking is because I'd like to know its uses more than just what was stated originally. As Ted said earlier and Marc followed up with, there are potentially more suitable alloys for a bright finish depending on what your part is shaped like and what it is being used for.

3003 polishes to an incredibly bright finish, and it chemically polishes very well also. But its downside is that its a very very soft alloy compared to the others they suggested, not to mention its only available in sheet/plate type structures that I know of.

IF your part is cosmetic in nature, and its capable of being made from 3003 sheet or plate. I'd seriously suggest you look into it. Its used extensively in the reflector category that Ted talked about.

Not to mention I think 3003 gives a beautiful colored anodize finish also. Outside of the pure base aluminum alloys, its what I would choose above and beyond the others if my project allowed for it.

Matthew Stiltner
plating company - Toledo, Ohio


popcorn machine parts
December 24, 2012

Q. Would anyone be able to tell me what kind of or grade of aluminum that would have been used in the late 40s as cast decorative or trim pieces. In particular an old popcorn machine. The parts originally had a brushed appearance and were anodized with what I'm assuming was clear. The parts had dulled and grayed considerably. Not realizing that the parts were anodized I tried buffing and buffing and buffing with zero to little affect. Man that stuff is hard! Finally figured out the problem and with a combination of blasting and sanding I removed the anodized layer and was able to polish them quite nicely. I'd like them to stay that way for awhile. Thought about clear coating with paint, nickel or chrome plating, or re-anodizing. I've heard paint tends to yellow over time. Opinions and thoughts please. Thank you.

Doug Porter
Hobbyist Restorer - Washington State, USA


December 26, 2012

A. Hi Doug. It's hard to guess what aluminum alloys would have been used.

Most clear coats won't yellow much, especially if not in sunlight (UV rays). Easiest would be the one-component types, which are quite thin.

adv.
You might try Everbrite [a finishing.com supporting advertiser], which is a single-component clearcoat.

Two-component automotive clearcoats are more difficult to apply, but thicker and probably don't need redoing for many years.

It is possible to anodize such parts but, particularly if they are castings, you'll probably lose much of the effort that you put into polishing them. (Anodizing converts the aluminum on the surface to aluminum oxide, which is essentially transparent, but aluminum alloys have other materials in them like silicon and copper, which turn gray or black in the anodizing process).

Regards,

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


December 26, 2012

thumbs up signThanks Ted. I appreciate your insight and quick response. The machine won't be exposed to UV so think I'll give the clear paint a go. At least that way if I screw up it'll be a lot easier to remove than plating or anodizing. Thanks again

Doug Porter
- Washington State, USA



Polishing anodized aluminum

October 7, 2016

Q. Greetings,

I am looking for a method to polish anodized aluminum to a mirror quality reflection (no distortions, no discoloring) and was wondering what the options would be for such an undertaking. I have used mirrored polished aluminum in works in the past and they 1) are extremely scratch-prone and 2) oxidize very readily when touched by an ungloved hand, and am looking for a viable solution (anodizing, coatings, etc.) Thank you so much in advance for your assistance.

Best,
Kim

Kimberly Kraczon
- Berlin, Germany


ASM Metals Handbook
0-15V 0-5A

October 2016

A. Hi Kimberly. Mirrors and reflectors are made by polishing the aluminum, then anodizing it...

You need to use a fairly pure aluminum that anodizes well, and keep the anodizing as thin as possible while still meeting your needs. The ASM Metals Handbook has an excellent chapter on the topic, with suggestions on aluminum grades, thicknesses, polishing methods, etc.

Regards,

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



August 25, 2019

Q. Hi

Planning on polishing a piece of aluminium to act as a mirror, however it will be placed outside under my front porch. As it will be outside facing the elements, I need to find a way to stop it from oxidising/tarnishing.

The purpose of this polished mirror is to reflect near infrared radiation, so the technique of reducing or stopping oxidation should not absorb much of the IR.

I could polish stainless steel, however polished aluminium reflects IR much better than stainless steel.

Would polishing aluminium to a mirror finish and then anodising it be a better option?

Thank you

Phong Tran
- Victoria, Australia


September 2019

A. Hi Phong. The best approach would be gold plating the reflector, but it might be prohibitively expensive. A thin anodizing on the polished surface should be fine, but some alloys make better reflectors than others, and electropolishing or brite dipping would be better than hand polishing (see topic 3584, "Aluminum reflectors: alloy selection and finishing" please).

Regards,

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

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2019 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.