Heat treatment is a controlled process of heating and cooling a casting to alter its microstructure and, with it, its mechanical properties. It is carried out after the casting has cooled and been removed from the mould, and before it moves to final inspection and despatch.
Not every casting requires heat treatment. But for applications where specific mechanical properties, stress relief, or dimensional stability are required, it is an essential part of the production process. At Maybrey, we carry out heat treatment in-house as part of our post-process capability.
The Main Types of Heat Treatment
Stress Relief and Annealing
Casting involves rapid solidification from high temperatures, which can leave residual stresses in the material. These stresses can cause distortion, cracking, or dimensional instability during subsequent machining or in service. Stress relief annealing heats the casting to a moderate temperature, holds it there long enough for the stresses to dissipate, and then cools it slowly. The result is a more stable, dimensionally consistent casting.
Full annealing takes the casting to a higher temperature and cools it more slowly still, producing maximum softness. This is used where the casting needs to be worked further, or where machinability is the priority.
Solution Treatment and Ageing
For aluminium alloys, heat treatment is frequently used to develop the material's full mechanical potential. Solution treatment heats the casting to a temperature at which the alloying elements dissolve into the aluminium matrix, then quenches it rapidly to retain them in solution. This alone produces a supersaturated and relatively soft condition.
Ageing, either at room temperature (natural ageing) or at elevated temperature (artificial ageing), causes the dissolved elements to precipitate out as fine particles within the matrix. This precipitation hardening is what gives aerospace aluminium alloys their characteristic combination of low weight and high strength. The T6 condition, solution treated and artificially aged, is the most widely used specification for aerospace aluminium castings.
Heat Treatment at Maybrey
We carry out stress relief, annealing, solution treatment, and ageing in-house for both ferrous and non-ferrous castings. Our heat treatment operations are covered by our ISO 9001:2015 and AS9100 Rev D quality management systems. For aerospace castings, heat treatment procedures are specified at the contract review stage and form part of the full traceability record that accompanies each batch.
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