Painting exposed aluminum tubes on an ultralight - which paint?

Purely for appearance I am thinking of painting exposed aluminum tubes on a ultralight a pale golden yellow. To save weight I suppose spraying would be best. What paint would be best? Will any paint stick to exterior aluminum for long? Do the "paint plus primer in one coat" products add any value?

 

You have to conversion coat the aluminum first, this removes the non bonded oxide layer on the surface of the aluminum and replaces it with something that is bonded to the aluminum. Then you can paint that.

 

Never tried ther paint-plus-primer stuff, but painted a lot of aluminum. Paint on aluminum as it sits has a life measured in minutes, almost. Aluminum forms a skin of oxide that offers little "tooth" for bonding. (Oxides are often created by some types of cutting fluids, and the oxide acts as a super-slippery lubricant in machine work.) That oxide needs to be removed, usually by acid-etching, and to futher protect the metal it is then treated with alodine to form an impermeable barrier to oxygen. The acid leaves microscopic pits in the metal for the primer to mechanically bond to. The paint bonds to the primer. Zinc chromate is the usual primer for aluminum, as the zinc will act as a sacrifical element to preserve the aluminum.

Yellow? Excellent choice. All other colors are wannabes. But today's yellows are nearly transparent because they no longer use lead in the pigments. Paint the surface white first, and the yellow will be brighter and you'll use less of it.

 

Mist some spray can self etching primer on and do the same with the paint. If it's more than a cover dusting, you are putting too much on. If it looks really pretty, it has too much paint on.

 

Try anodizing. You can do that yourself, and make it just about any color.

 

'Pretty' anodising seriously reduces the fatigue life of Al.

 

Thanks Dan. With these key concepts I can find what is needed.
This is the kind of clear and detailed help that is the best of the HB forum.

 

Let me add something else to the list for your consideration:

https://www.aircraftspruce.com/catalog/cspages/prekotesurface.php

Dale
N319WF