I was looking around on the web the other day and as a fan of Cobra cars having had the opportunity to drive a real 427 Cobra back in the 60's, body damage requires a special technique for aluminum and I found this video that really says it all. It's well worth watching.
It took him several hours to fix that fender and I bet the repair was not cheap. I don't know what alloy that car was made of. Many of these aircraft alloys do not take well to heating and welding. If you anneal the metal it will still be soft when you finish the repair although the amount of cold work he did with the hammering will harden the metal to some extent. He did not also have flammable stuff around the metal.
I did enjoy the video though. Nothing like seeing a true craftsman work.