Optical Coating on Aluminum 6061-T6 Base Material

Get in touch with Eastman Chemicals - sound like what you need could best be made from one of their Cellulose acetobutyrate resins. They are excellent especially at light resistance. They will probably refer you to one of their clients in your neck of the woods.

Look up Cellulose acetobutyrate on the web.

seems to me that paint would be your best option.

it meets all of the above criteria

You do not mention the reflectivity and wavelength requirements of the mirror. Bare aluminum is rarely used in optical systems as a reflector. The reason being that silver and gold have much higher reflectivity in general than aluminum. The substrate is generally polished and then coated with silver or possibly gold depending on the wavelength requirements. The reflective film is then overcoated with a dielectric material to protect the fragile reflective surface. Again, the choice of dielectric is determined by the wavelength requirements of the mirror. This is the best way to insure a good optical reflector.

Aluminum is poor reflector compare to gold and silver. Gold is best but to protect gold you may need coating which is transparent to light and Eastman Kodak is good place to get resin for Cellulose family and work with them

"1.1.2. No gold, silver, aluminum or other metallic reflector layer material shall be exposed to atmosphere."

Sounds like the OP is making a common mistake of referring to the base metal as the top layer. This happened all the time to me in a past life. The inexperienced engineer comes in to the lab and says, I need a paint that sticks really well to Al. Then he shows up with an Al box already coated/painted with some material. The typical response is, "well, the box is aluminum."

So, the question is, what will the coating come in contact with, when the object is coated? If it is Al, remember that as soon as the object comes in contact with the atmosphere, oxides will form that must be removed prior to coating. Coatings don't stick well to aluminum oxide.

Hi,

if you need a solar concentrating reflector then you may polish the 6061 directly and then overcoat by a very thin clear anodising.

If you need the very best reflection available, then you have to choose a better alloy ("Reflectal") in former times, same protection by anodising.

If you need an optical imaging system with strict requirements on quality you will have to:

1. stress relieve your Al6061

2. cut by diamond turning or fly-cutting the desired shape

3. polish to required residual surface roughness (if below 15nm)

4. Overcoat with pure Al (minimum 99.99% purity) by vacuum evaporation or sputtering or ion plating.

5. Overcoat by anodising or vacuum (any transparent material) if reflection of 92% is sufficient, overcoat Ca- or Mg-fluoride if near one wavelength a better reflection is required, by multiple layers (high and low refractive index) if at 2 or more wavelengths a much better reflectance is needed.

Think in advance about mounting stress and deformation.

Have a look into the book: Musicant, "Optical Materials".

Try and learn or go and buy or both.

RHABE