What material does a weld not stick to?

[Gary Fowler]

Copper plate for backing then tack weld it alternating the locations to keep the angle straight. It is going to be a challenge to keep it straight. Bolting the other angle to the one you are welding might help a bit to keep the welds from drawing too much but you still need to weld opposite side from the bend as the previous weld cools it is going to contract and pull the angle.
Shield Arc might can explain it better.

 

[Shield Arc]

Shield Arc might can explain it better.

Oh I don't have the words to explain how to do it. I can show you how tho.
Angle iron, as with square tube is easy to bring back straight after welding.

 

[ray66v]

Copper works fine, unless you are welding copper. :thumbsup: