Postanneal mechanical properties of prestrained AA5182-O sheets

The effects of different prestrain levels, paths, and subsequent annealing on the postannealing mechanical properties of AA5182-O were investigated. Aluminum sheet specimens were prestrained in uniaxial, plane strain, and equibiaxial tension to several equivalent strain levels, annealed at 350 °C for short (10 s) and long (20 min) durations and then tested for postannealing mechanical properties, including tensile properties, anisotropy, and forming limits. The tensile properties, R-values at 0, 45, and 90 deg relative to the sheet rolling direction, and forming limit diagrams (FLDs) exhibited dependencies on prestrain 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 backscatter 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.