They may be further strengthened by strain hardening procedures, or by cold working. A system of letters and numbers to indicate temper have been approved by the American Standards Association. In this system the basic temper is designated by a letter, whereas modification of the temper is indicated with a number. T Heat treated T indicates the heat treatment and the number that follows T indicates the modification on the heat treatment process. Pure copper is alloyed with many other elements to produce minor changes in properties.
Pure copper is a single phase alloy.
Copper and its alloys may be classified in many different ways.