Quenching

The purpose of quenching is to lock into solution the solute elements by rapidly cooling to a temperature usually near room temperature. Various quench mediums can be used, which are all water-based, as follows:

• Water (room temperature)
• Hot water
• Boiling water
• A solution of water plus Poly Alkaline Glycol (up to 25% of PAG)

The purpose of the quench-medium modification is to reduce the risk of distortion and, in particular when using the PAG, to provide a uniform heat transfer from the workpiece to the quench medium.

Strengthening By Precipitation Treatment

Generally the heat-treatable aluminum alloys are artificial aged at temperatures between 200°F and 400°F. Once again, temperature accuracy, temperature uniformity and time at temperature are critical to this strengthening.

Over-aging will result in a reduction of yield strength and tensile strength as well as deterioration in the hardness value.

Natural aging of certain aluminum alloys can be accomplished at room temperature. Generally, the full mechanical properties will be achieved in approximately 96 hours or less.

Although the thermal treatments of the heat-treatable aluminum alloys occur at significantly lower process temperatures of that of steel, great care and attention must be paid to:

• Process temperature selection
• Time at temperature
• Transfer to quench medium
• Precipitation treatment temperature selection