Practical ageing in the extrusion plant (Topic: 10050)

For age hardening of extrusions the heat-treatment is carried out in three successive steps:

1. Solution heat-treatment at a temperature above the solubility curve. For extrusions this is done by extruding with a combination of speed and preheating temperature of the extrusion ingot, such that the extrusion has a temperature well above the solution temperature, when it enters the run-out table.

2. Quenching at the run out table, either by air, forced air or water. Sometimes boiling water is used to reduce quench stresses.

3. Ageing (precipitation) at room temperature (natural ageing) or at elevated temperatures up to 200°C (artificial ageing). For 6000-alloys the combination 185°C for 5 hours is most frequently used for artificial ageing.

The steps in the age hardening of a typical 6000-alloy is shown in the figure below.

Schematic diagram showing the age hardening of 6000-alloys in the extrusion plant.