David, wot's it for? Does it require strength, is it going to be wet often, that could create a galvanic effect, causing corrosion. The ideal would be steel angle, but if you are like most of us you just have to use what ever you have.
On one of my hot air engines, it has a copper cooling hopper, and I tryed a bit of extra cooling by puting an aluminium heatsink in the water. After the motor had been running a while I thought about the galvanic effect, so I put the volt meter across the copper, and aluminium, and got .5 volt, with just plain tap water. Ian S C