I have a cousin who uses a wheelchair, it seems unfortunate, but now they have a wide variety of formats to meet specific needs for their users, so it's not as bad.
My brother, who died in 1998, used a wheelchair that was heavy and hard to use.  Today, you are right, there are many more lightweight options.
I'm sorry to hear about your loss. Yes they are lightweight now and have specialized seating adaptions, individualized controls, and other features to help efficiency and ease of use.
Are there any that are aluminum and foldable?
I don't know for sure, but I would certainly imagine so. I know they even have ones specific for activities like sports wheelchairs, so I'm sure aluminum foldable ones exist.
Right now I'm looking for an aluminum and foldable wheelchair ramp for my mother.  Everything related to wheelchairs take up a lot of space.
That's true they are kind of a large apparatus, are you looking to build a permanent, semi-permanent, or portable ramp?