When we say aluminum extrusions’ “temper” designation, we mean that the material has been taken through heat treatment. The heat treatment is meant to enhance the properties of the material for use in aerospace applications or any other specific area. A good example is T6, which starts with solution heat treatment and then artificial aging. The result is an alloy that has the highest strength. For T4, there is no aging with solution heat treatment. The resulting material may be not as strong as T6, but its formability is better. Each of the other tempers has a unique heat treatment process that results in unique characteristics.