Aluminum-copper solution annealing

Solution annealing for aluminum-copper alloys is done to evenly distribute the alloying elements in the base material again. That's the preparation for hardening, otherwise the material won't harden uniformly and can crack later. You heat the part to the right temperature, hold it for the correct time, and then quench it quickly to freeze the state. If you anneal too short or too hot, you'll have trouble with hardness afterwards.