[mickmate]

Copper has been described already to anneal or soften. The key is in the cooling process. Copper is cooled slowly gradually reducing the heat. Aluminium is heated to a temp close to melting, be careful because it doesn't get red hot it goes glub. A good indicator is bar soap rubbed on it and when it burns or turns black it is cooked. It can be easily heated with a plumbers torch or a mapp gas torch. The big difference is in the cooling you dunk aluminium in water to cool it rapidly. Both make good gaskets and have high thermal conductivity to sink the heat away, if you have a real nice metallic match on both surfaces I would consider just the HiTemp RTV. You'll make it work they don't have much back pressure to worry about!
Cheers Nick