We build subsea machinery, and whenever we build them out of aluminum, the ongoing corrosion issues are overwhelming.
Aluminum "disappears" very quickly in salt water due to corrosion. Special post-construction surface treatments such as anodizing are fine for objects no larger than a car, but what about all the miles of welds and crevice corrosion locations on/in the boat.
If something breaks or leaks, drive to the nearest port and you'll likely find a shade tree welder-maybe even a crew member-enough to fix the welded steel together. aluminum? Special machine. Special filler. Being able to perform structural welding on aluminum is not a skill that is very common around the world. Being able to perform pressure welding is very rare.
A shift in this direction may be possible in the future, but the infrastructure required is a tricky proposition.
