Why is old aluminum scrap often used to make casting alloys?

"Old" aluminum scrap—which is generated from discarded consumer products like automobiles or lawn chairs—is frequently used to produce casting alloys because of its composition and condition. Unlike "new" scrap, which is typically well-defined and can be returned to primary producers to be remade into the same alloy, old scrap is often dirty and consists of a mixture of many different alloys.1

Because this mixture of materials makes it difficult to isolate specific chemical compositions, the scrap is ideally suited for casting alloys, which naturally contain higher levels of various alloying elements. These casting alloys are designed to incorporate such elements to achieve specific metallurgical properties, such as strength, ductility, or wear resistance, making them a practical and efficient destination for recycled material.12