One problem you might encounter with this project is that if you heat the aluminum to approximately 500 deg F or above . . . any heat treatment in the frame will be gone. In other words . . . any aluminum in the heat affected zone will be soft. I have tested 6061-T6 @ 500 deg. Other alloys might react differently.
I was involved years ago in the manufacture of an aluminum-framed bike formed with .065 sheet aluminum. The aluminum alloy used was 6061-T0 [zero]. Once it was formed and welded . . . it was sent to a heat-treat plant and was brought up to T6 condition to make it strong enough. Any welding done later would have ruined the frame.
YMMV.
DON