Mixing more than 1 elemental Mineral , molten, in a Metal is called alloying . Industry assigns Numbers to differentiate what is in the Alloy Mix.

The common designation for Chrome Moly Steel .. is 4130.. Trade marked Products have other names they chose.

Aluminums also have Numbers.. 6065 is specific as is 7001 the first number of the group tells you the largest % of non aluminum added.

the 1000 group is pretty much all aluminum OTOH 7000 adds Zinc.

GENERAL ALUMINUM INFORMATION from Aircraft Spruce