Once the heat-treatable aluminum alloy has been successfully solution treated, the next treatment that is necessary in order to achieve higher mechanical properties in conjunction with hardness will be to allow the alloy to go through what is known as artificial aging.
It must be pointed out that the heat-treatable aluminum alloy will naturally age hard. That is to say that if no further heat is applied to the alloy, the alloy will naturally age to its maximum mechanical properties and hardness. This will take time, ranging from a few days up to years to complete at room temperature, depending on the alloy composition/type. In order to accelerate the aging process, therefore, heat is applied to the solution-treated aluminum alloy.
The process temperatures – 200°F up to approximately 400°F – can be selected for the artificial-age procedure. There can also be a treatment that combines cold working plus thermal accelerated aging. This will, of course, depend on the aluminum alloy and the specification requirements.
There are three critical considerations for the artificial-aging process:
- Process temperature selection
- Process time at the selected temperature
- Temperature uniformity
It is necessary that the uniformity of the aging furnace has a temperature variance anywhere within the process chamber of +/-5°F. Temperature uniformity is absolutely critical with this procedure. Once again, if there are significant temperature variances within the process chamber, there will be mechanical and metallurgical differences in the treated component.
The physical properties that are generally achieved by applying the artificial-age/precipitation-hardening process are tensile strength and yield strength, whereas ductility and toughness will decrease.
We will conclude this discussion next time in part 2.