Electrical Motor filler metal for laminated stacks
That is the rotor of a squirrel-cage induction motor. The aluminum makes the shape of a squirrel cage to form the electrical conductors in the rotor. The material must be pure enough so that the resistance is not too high. However it may contain something to increase the strength.

Here is a specification that I found:



Malcolm Burwell  et al, Improving the High Speed Efficiency of xEV Induction Motors, Society of Automotive Engineers of Japan, Inc.