What does the 'T' designation refer to in the temper designation system?

The 'T' designation in the temper designation system specifically indicates that the aluminum alloy has undergone a thermal treatment process, making it heat treatable. This designation signifies that the alloy is capable of being strengthened through a solution heat treatment followed by aging, which enhances its mechanical properties such as strength and hardness.

Heat treatable aluminum alloys can achieve significant improvements in performance through these heat treatment processes, allowing them to be used in demanding aerospace applications. Therefore, the 'T' designation is crucial for identifying alloys that benefit from heat treatment, which differentiates them from non-heat treatable alloys that might have different temper designations, such as those that rely solely on cold working for strength enhancement. In the context of aerospace materials, the proper understanding of these designations aids in selecting appropriate materials that can withstand operational stresses.