Heat Treating Aluminium [Easy DIY method]

[jimirwin]

Nice but minimal introduction to the topic.
You do not mention the specific alloy(s) or family of alloys you're using.
Makes a HUGE difference!
You also mention casting the alloy. 60xx alloys are wrought, typically rolled or extruded.
Smelting and casting these makes them something different.
T5 is an artificial aging heat treatment to some common aluminum alloys. 6063 or 6061 typically.
Increases hardness and strength.
Water quench from above critical temperature actually anneals the same alloys.
Water quench from elevated temp simply stops the heat treatment process at that time.

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Each alloy family has its own processes. Some are quite unique. I worked in an aluminum alloy extrusion and door & window manufacturing company as an intern during my senior year. One of my jobs was to study and characterize heat treatment of 6061/6063 alloys using the metallurgy labs at Texas A&M.

I also worked in the physics dept machine shop during my junior year. (Been a metal cutter/mangler since age 10...73 now!)

heat treating, as we have come to call it, is really artificial aging. i.e. the same physical properties will develop over time even under normal temperatures. Elevated heat just speeds the process.

Other alloys have their own processes.
7075 high strength alloys have a troubling propensity to change dimensions over time. One must design in such considerations.
Just one of many examples.