Glossary
T5 temper — definition
A temper in which the part is artificially aged straight from the casting temperature, without a separate solution treatment.
T5 takes advantage of the part already being hot when it leaves the mould. It is cooled and then aged under control at a moderate temperature.
The strength gain is smaller than with T6, but the process is faster, cheaper and causes less distortion — the part moves less because it does not go through a quench.
T5 is therefore often the practical choice when you want additional strength without taking on the full cost and risk of a complete solution treatment.