Aluminum heads are made of cast aluminum alloy. Working from memory, the chemistry is somewhere around 11% silicon, 3% copper with the rest aluminum.

Clean aluminum to the secondary market generally means all other metals and nonmetals are stripped from the aluminum piece. The most important metal to remove is steel. Iron is considered a poison to aluminum alloys. Small amounts can drastically reduce the desirable material properties of an aluminum alloy. Most foundries try to limit the composition of their secondary aluminum to one percent iron.

Removing steel is very difficult on an aluminum head. The valve guides and valve seats are pressed into the head. Anything done to remove the steel will help raise the quality of the scrap. If the aluminum goes through a shredder and magnetic separator, it may not matter.

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95 E320 Cabriolet, 169K