Aluminum polished to mirror finish?

[treborly]

Is it possible to get a true "mirror finish"?


Also, what's the thermal expansion ratio of aluminum?

[treborly]

well, nvm. Just found out.




http://metku.net/index.html?path=mod...ttle/index_eng

[imagineer]

Thermal Expansion for aluminum = .000,013" (microinches) per degree F.

Keep in mind, not all aluminum alloys will polish equally. I work with extrusion and 6061 alloy won't polish nearly as well as 6063, which does not polish as easily as 6005 or 6463.

[treborly]

Thermal Expansion for aluminum = .000,013" (microinches) per degree F.

Keep in mind, not all aluminum alloys will polish equally. I work with extrusion and 6061 alloy won't polish nearly as well as 6063, which does not polish as easily as 6005 or 6463.

Thanks.

Ya, i got to look into what aluminum is best to get a mirror finish.

[treborly]

Wont aluminum oxidize very quickly though? I cant imagine a mirror finish lasting very long at all.

i`m working on a project where i need to polish alum to a mirror finish, problem is i cant put any clear coat to protect the finish.

My first choice was using Tin instead of alum , then i looked up the price of Tin............





EDIT
Well i was looking some stuff up and apparently the aluminum oxide can be highly transparent. If thats the case, why do telescope mirrors get re-aluminized every 6-12 months?

[enlpck]

Well i was looking some stuff up and apparently the aluminum oxide can be highly transparent. If thats the case, why do telescope mirrors get re-aluminized every 6-12 months?

Dust is a big reason (the mirror is directly exposed to the elements when in use). Also, the layer of Al is tremendously thin (so as to keep the shape of the glass), and as the oxide grows over time (it slows down, but never really stops) I wouldn;t be surprised if the oxide growth causes distress in the underlying coating.

On material where you don't need perfection to 1/8 of a wavelength of light (0.05 micron or so, which is about 2 millionths of an inch), all the oxide layer will do is protect the surface. It is tough. It is sapphire (one of the hardest materials short of diamond)

Tin would be a bad choice. The oxide is in no way transparent, and isnt very adherent to the base metal, either.

[treborly]

How fast does the oxide form on a fresh piece of aluminum? IS there somewhere where i can find the "growth rate" of aluminum oxide?


I need to sand and then polish it to a mirror finish. I need to know how long i can wait after i sand, before the oxide will form.

[Tux_Rules]

Probably not the best info, but a start:

http://en.wikipedia.org/wiki/Aluminium

[ptsideshow]

The oxide starts as soon as you stop removing it, It is slow acting for the most part, But depending on the conditions it is placed in corrosion(oxidation) can happen faster if the combination of moisture and trace elements (salts, etc) temperature are right!