Cosmic's July '66 Brochure stated "Light Alloy Road Wheels LM6 to B.S, 1490.
Attached Word doc with composition of both LM6 & LM25 Alloys. Pretty much all useful aluminium alloys will have a wee bit of magnesium, and the % of magnesium in, for instance, Cosmic's MK1 & MK2 wheels was very low.
Cosmic Alloy Wheel Composition.docx