Cyclic bending under tension of alloy AZ31 sheets: Influence on elongation-to-fracture and strength

This paper describes the main results from an experimental investigation into the consequence of cyclic bending under tension on elongation-to-fracture (ETF) and strength of AZ31 sheets. The deformation is imparted on test specimens of the alloy using a recently built continuous-bending-under-tension (CBT) apparatus conceived to increase ETF relative to simple tension (ST). The apparatus pulls the specimen in tension with a certain velocity while the specimen reciprocates through a set of three rollers, which impart a given amount of bending. The parameter space consisting of bending depth, crosshead velocity, and sheet thickness is explored to achieve the greatest ETF for the alloy. However, only moderate improvements in ETF are obtained. The small improvements are attributed to the relatively uniform elongation of the alloy during both CBT and ST with a small amount of the remaining ductility to deplete throughout the sheet by CBT after exhausting the uniform elongation. Mea-surements of the grain structure and texture evolution using electron-backscattered diffraction and neutron diffraction reveal slip dominated deformation with some twinning followed by de-twinning. The behavior of the alloy upon CBT processing to a certain number of CBT cycles followed by heat treatments (HT) is also investi-gated to achieve tradeoffs in strength and ductility. Results and insights from these investigations are presented and discussed. Significantly, it is shown that the strength of the alloy can be increased for over 30% while preserving at least 5% of its ductility.