Post-anneal mechanical properties of pre-strained AA5182-O sheets

The effects of different pre-strain levels, paths and subsequent annealing on the post-annealing mechanical properties of AA5182-O were investigated. Aluminum sheet specimens were pre-strained in uniaxial, plane strain and equibiaxial tension to several equivalent strain levels, annealed at 350°C for short (10 seconds) and long (20 minutes) durations, and then tested for post-annealing mechanical properties, including tensile properties, anisotropy and forming limits. The tensile properties, R-values at 0°, 45° and 90° relative to the sheet rolling direction, and forming limit diagrams (FLDs) exhibited dependencies of pre-strain and annealing history. The importance of the process variables and their effects were identified via designed experiments and analysis of variance. Three-dimensional digital image correlation, which captured the onset of local necking, was employed in the FLD development. Texture in the as-received and deformed sheets was investigated with electron backscattered diffraction and provided a means for linking prestrain and static recovery or recrystallization with microstructure. This guided the understanding of the mechanical property changes observed after preforming and annealing. Ultimately, the expanded forming limit curve demonstrated the advantage of annealing in extending the formability of strained AA5182-O.