Deformation and failure of a superplastic AA5083 aluminum material with a Cu addition

A modified AA5083 aluminum sheet material containing a Cu addition of 0.61 wt pct has been investigated under conditions relevant to commercial hot-forming technologies. This material was produced by continuous casting followed by industrial hot and cold rolling into sheet. Deformation and failure mechanisms at elevated temperatures were investigated through mechanical testing, thermal analysis, and microscopy. The effects of Cu addition are evaluated by comparisons with data from AA5083 sheet materials without Cu addition, produced both by continuous and direct-chill (DC) casting techniques. At low temperatures and fast strain rates, for which solute-drag (SD) creep governs deformation, the Cu addition slightly increases tensile ductility at 450 degrees C but does not otherwise alter deformation behaviors. At high temperatures and slow strain rates, for which grain-boundary-sliding (GBS) creep governs deformation, the Cu addition decreases flow stress and, at 450 degrees C, improves tensile ductility. A strong temperature dependence for tensile ductility results from the Cu addition; tensile ductility at 500 degrees C is notably reduced from that at 450 degrees C. The Cu addition creates platelike particles at grain boundaries, which produce incipient melting and the observed mechanical behavior.