We manufacture Aviation gearboxes, we use ( castings ) CC601 heat treated to T6. We cast, fettle, rumble, heat treat to T6, involves bringing the castings to nearly melting for I think about 16 hours then quench . Then some other process after at about 200 degrees for a few hours. This is done by Heat Treatments in NZ. The castings post heat treating are very strong and machine well. I did talk to Heat treatments about treating an alloy frame after welding and was told by rights it should be taken back to T0 ( whole frame ) then re heat treated to T6 again. This would probably distort the bearing housings already machined, so I didn't bother.