Eliminate Grain Coarsening in Aerospace Alloys During Processing

In the aircraft industry, aluminium sheets are most commonly formed in their soft state, followed by solution heat treatment and natural or artificial aging. If the deformation in the working process exceeds a critical amount, grain coarsening occurs during the subsequent recrystallization at the solution heat treatment. A later deformation to this condition leads to orange peel surface, which requires an additional polishing. Furthermore the coarse grain leads to a drop in the mechanical properties, often below specification limits. If there is no subsequent deformation after the heat treatment, this effect is not visible and without destructive testing there is no possibility to detect the error.

Beside the common containment actions like initial grain size and chemical composition there are some special process routes to improve the resistance against grain coarsening during processing. The first determining factor is the process route for the sheets itself. AMAG investigated different sequences of rolling steps and heat treatment and creates various mechanical properties in the same temper. A component manufacturing with different deformation degrees was simulated in the laboratory. The microstructural evolution shows that some sequences should be preferred. Secondly the final processing can influence the resistivity against grain coarsening in a huge amount.

Furthermore with a finely tuned process route it is possible to reduce production costs, which is an additional benefit for customers.