i did some messing with the aluma weld or muggy stuff its stronger then you think it is . takes some work to get it to stick but doing some hammer test and beat the living shit out of it the plate gave up before the weld did . as for the rim what there made from .....
a zamc alloy of one of many mixes
A356 "industry standard" for casting aluminum
or some cheap bargain alloy from the plant .
about the only way you could find out is to talk to some one who was in charge of casting them or find some one who can do a assaying (spelling?) where you send in a chunk and have it tested .
or maybe if the scrap yards around you are high tech they may have one of the id guns where they can point and pop it and it will give you a basic break down of its make up .