Stretch forming of both fuselage and nacelle skins often requires multi-stage processing to achieve the final form. Finding
the optimum pre-strain level before inter-stage annealing is critical to avoid failure in subsequent processes and minimise
the number of processing steps. This paper examines the effect of three pre-strain levels of 4%, 8% and 12%, followed by a
recovery anneal process. Both yield behaviour and material formability are analysed. The forming limit diagrams indicate an
immediate drop in formability in the pre-strained and annealed samples when compared with the O condition material. The aforementioned
formability drop quickly saturates for the higher pre-strain magnitudes. This saturation is also evident in the uniaxial data.
The underlying material texture, as described by the r-values, remains unchanged during processing, while the yield strengths
are shown to increase in an almost isotropic fashion. Overall the paper indicates that to improve the formability in subsequent
processing steps, the pre-strain levels should be maximized before the recovery anneal and second forming stage.
Key words Aluminium - 2024 - Annealing - Formability - Stretch Forming