Which sequence correctly describes precipitation heat treatment steps?

• A. Heat, quench, then reheat at a lower temperature for a specified time, then air cool
• B. Quench, then air cool
• C. Heat, air cool, then quench
• D. Heat, reheat at a higher temperature, then air cool

Answer: (A)

Precipitation hardening relies on three steps: dissolve soluble elements by heating to a solution-treatment temperature, lock them in a supersaturated solid solution with a rapid quench, and then age at a lower temperature to form fine precipitates that strengthen the material. The best sequence follows this order: heat to dissolve the alloying elements, quench quickly to preserve the supersaturated state, then reheat to a lower aging temperature for a specified time to precipitate particles, and finally allow the part to cool (often by air cooling). This aging step at a lower temperature is what creates the fine, dispersed precipitates that harden the alloy. The other sequences miss the aging step, place cooling or quenching at the wrong time, or attempt aging at a higher temperature, which would either not produce the desired precipitates or could dissolve them already formed.