If you have a rotary wire brush that fits on an electric drill, that should clean that corrosion right up. Follow that with some wet sanding with #400 sandpaper. (You have to keep it wet or it will clog up the grit almost immediately.)
If the wire brush doesn't take that right off, try #220 sandpaper. Sand lightly, just enough to remove the white stuff and smooth the affected area. Then wire brush, then #400 sandpaper.
Whenever you sand or wire brush aluminum, use a <---> action, not circular, and not left/right and up/down. When you get to the #400 wet sanding, you should begin to see a nice even shine. It is possible to step up to finer grit, but on aluminum that is only productive up to around 800 to 1000 grit. Anything finer is for restoring scratched plastic or polishing up automotive finishes.
I am doing that to those 30# alumninum propane tanks that I found, and they clean right up. They are 38 years old and have a lot of accumulated oxidation and staining.
After you clean it, it is possible to coat or paint the alumninum to prevent further oxidation, but whatever you coat it with will eventually transfer to the awning fabric. Better to rub on a coat or two of automotive wax and buff it off.
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