Heat Treatment of Aluminum Alloy

[the_dialogue]

During the heat treatment of Aluminum alloys, two processes: Solution and Precipitation heat treatment were used.

Should the hardness increase or decrease from the original alloy after solution heat treatment? My reference text says that the material should be "soft and ductile" after solution heat treatment, but I am not sure if this is accurate.

What should be the effect on the hardness after Precipitation heat treatment? I was under the impression that this final hardness should be significantly higher than the original alloy and higher than the hardness measured after solution heat treatment.

Thank you.

 

[Astronuc]

Solution annealing generally softens (reduced strength) a material, while precipitation, which usually means precipitation of 2nd phase particles or intermetallics, usually hardens (strengthen) an alloy. Aging, or age hardening is also a term used for precipitation hardening.

Solution treatment involves heating the aluminum to a temperature of 430-540°C (800-1000°F), at which alloying constituents are taken into solution (i.e., brought near their melting point) prior to a rapid quench. This rapid quench retains the grain structure but leaves the material soft, requiring a subsequent aging operation. The heating time and temperature is dependent on the alloys contained in the aluminum and the cross-sectional thickness of the material.

https://www.industrialheating.com/b...solution-heat-treatment-of-aluminum-fasteners

After solution treatment and quenching, aluminum fasteners are age hardened at elevated temperature, which is also referred to as precipitation heat treatment. The aging process increases the strength and hardness of the material. Aging requires temperatures of 115-200°C (240-390°F) and heating times of 5 to 48 hours. The time-temperature parameters for aging are carefully selected based on the alloy used and the desired mechanical properties.