Powder Coating Billet Aluminum

I was reading an article in a trade magazine last week and thought I would pass this on. Many of you probably know this, but if you choose to powder coat billet aluminum, you need to pay careful attention to bake temperature. If you get to 410F, it will change the structure of the aluminum, making it very brittle. Make sure that whatever powder you are using will set well below 410F so that the part is not adversely effected.

 

[40 Bud]

Great point Pat. Reminds me of something I was told some years ago. I had to powder coat many different aluminum castings during the rebuilding of food processing equipment. At that time I was told that application of high heat to cast aluminum was a cummulative thing. Anybody know if that is true?

 

[Mark Worthington]

Wouldn't this really be dependant on the type of aluminum allow and prior heat treating employed?

As for cumulative effects, I doubt it; you either get to a temperature at which the crystals can re-arrange themselves in the solid matrix or not. Then again, I'm no metallurgist.

 

[Bill Musarra]

I understand the idea you are talking about, but wouldn't it be simpler, and probably look just as good, to consider anodising(?). I'm not sure if it has a down side, such as the brittleness factor.
Bill

 

I now have the article in front of me, which states "The Aluminum Association Inc. describes it this way: Heating aluminum alloys above 275F causes granular rearrangement of the metallurgical structure resulting in a significant change of bulk properties. Essentially, the tensile strength of the metal is dramatically lowered, much like a stress relief anneal on a piece of steel would do."

I wonder what I may have done to my rear upright as I ended up putting one of them in the oven in an attempt to get the bearing in?

 

[Chris Duncan]

Most aluminum for fabrication is in a hardened condition, typically a heat treatment.

With an alloy designation say 6061 T6, the "T6" is the hardness. With a zero hardness meaning normal condition.

When you heat an aluminum part to a certain point (I'm not sure what it is but I think 400F is close) it brings the part back to normal condition, or zero.

That's why anodizing is a better way to coat aluminum and hard anodizing is the best anodizing, it's makes the surface harder.

Parts that have lost their hardness due to welding or inadvertent bearing installs <grin> can be re heat treated for a nominal fee, but warpage can occur, that's why parts are usually machined after being hardened.
There is also hardness testing to see if the hardness has been lost.

One of the "to win" series by Carrol Smith has a good chapter on aluminum alloys, there's also some good info on the web, I'm not at home right now or I'd post a link. .