I recently purchased a Questus self-leveling radar mount off of Ebay.
Unfortuantely this unit was designed to be mounted on a backstay, and my
boat (a Freedom 40/40 with a carbon fiber mast) doesn't have one. I've
designed an adapter for it, which I will machine out of 3" round Al stock.

It seems that there's primarily 2 types of Al stock available: T6511 and
6061. The part will be painted. Which of these (or some other varient)
should I use considering the salt water marine environment?

-- Thanks, Geoff