Critical to quality characteristics of AA2024 sheet material for aircraft skin application

New findings from AMAG research and modifications made to alloy AA2024 have made it possible to improve the workability of the components made out of AMAG aircraft sheets. Those characteristics, which are critical to quality for specific products for the customers, have been identified and the process variables that affect those characteristics are controlled. A significant difference between a generally globular fine grain and elongated coarse grain material was observed regarding intergranular corrosion resistance as well as fatigue crack propagation behaviour. The adjustment of the grain size and to keep it stable within tight tolerances is also crucial for a cost- and time reduced manufacturing of the final parts for the aircraft. By maximizing the creep resistance the distortion of the components during forming and heat treatment can be reduced and the time needed for removing the warpage minimized. Another example which will be described in detail in this work is avoiding grain coarsening. Forming of a component followed by solution annealing can result in a significant increase of the grain size causing a drop in mechanical properties below specification limits. These changes in material properties can often not be detected on the finished part. This phenomenon was analysed in detail and can be reduced by adding micro alloying elements. The appropriate rolling procedures aiming at variations in grain’s shape and size to control those quality characteristics are described which allow customers to lower their costs.

These investigations are part of AMAG`s ambitions to extend the aircraft product portfolio and is underlined by recently achieved new qualifications for outer-skin material which meet the highest demands on material properties and surface quality.