For hobby car racers it is DIY. The welding equipment is pretty central to their hobby. However they will also have a lift to take the engine out of a car - pretty abnormal for most people
.
Myself I tried soldering alu, following two different processes in the market, and I would not recommend it to anyone. The chances of destroying the soldered items was at 50% or so. If a joint was achieved, it would not be strong. Welding of alu is, of course, done regularly and correctly done joints hold well.