Alloy Steel 7075 - widely used in the Aerospace industry

A four-digit numerical designation system, developed by the Aluminium Association, is used to designate wrought aluminium and aluminium alloys. The first digit defines the major alloying element in the 2xxx through 8xxx alloy series, the second digit in the designation indicates the alloy modification. When the second digit is zero, it indicates the original alloy. The numbers 1 through 9, assigned consecutively, indicate modifications of the original alloy. Explicit rules have been established for determining whether a proposed composition is merely a modification of a previously registered alloy or if it is an entirely new alloy. The last two of the four digits in the 2xxx through 8xxx series have no special significance but serve only to identify the different alloys in the series.