This paper presents results acquired from experimental investigations into determining the influence of cyclic-bending-under-tension (CBT) and annealing on elongation-to-fracture (ETF) and tradeoffs ...in strength and ductility of three Mg sheet alloys: ZEK100, BioMg250, and Mg4Li. The CBT process imparts uniform deformation greater than achievable in simple tension (ST) incrementally by subjecting a sheet specimen to simultaneous tension with a crosshead motion and bending with a set of rollers reciprocating along the specimen. The space of process parameters including crosshead velocity and bending depth is explored initially to achieve the greatest ETF of ZEK100 alloy. Improvements in ETF of about 40% are attained using CBT relative to ST. Given the uniform deformation imparted by CBT to large plastic strains, tradeoffs in strength and ductility of the alloy are investigated next by subjecting the alloy sheets to a certain number of CBT cycles under the optimized parameters and subsequent annealing. Strength of the alloy is found to increase by a factor of 1.4 along the sheet strongest direction, the rolling direction, and a factor of 2 along the sheet softest direction, the transverse direction. Since the strength improved more along the soft direction than along the hard direction, the alloy anisotropy reduces. Significantly, the strength can increase for about 40% along the soft direction, while reducing the anisotropy and preserving at least 10% of the alloy ductility in every direction. Characterization of microstructural evolution using electron-backscattered diffraction and texture evolution using neutron diffraction revealed slip dominated deformation of the alloy. Similar processing and testing of BioMg250 and Mg4Li sheet alloys produced even better results in terms of enhancing elongation and improving the contrasting strength and ductility properties. Comprehensive data for the three alloys and insights from the investigations are presented and discussed.
•Over 3-times improved elongation of cp-Ti sheets is achieved by cyclic-bending-under-tension relative to simple tension.•Tradeoffs in strength and ductility of cp-Ti can be optimized using ...cyclic-bending-under-tension and annealing.•Strength increases owing to stored dislocations since insignificant twinning and grain refinement were observed.•Measurements of the grain structure and texture evolution reveal slip dominated deformation in the material.•Directional hardening and underlying microstructural changes during cyclic-bending-under-tension can reduce anisotropy.
This paper describes results acquired in an investigation into determining the influence of cyclic-bending-under-tension (CBT) and annealing on improving elongation-to-fracture (ETF) and optimizing strength and ductility of commercially pure titanium (cp-Ti) sheets. The space of process parameter involving crosshead velocity and bending depth along with sheet thickness was explored to establish a set of optimal parameters providing the greatest ETF for cp-Ti. Enhancements in ETF of about 3× were achieved using CBT relative to simple tension. Given the uniform elongation facilitated by CBT to very large strains, tradeoffs in strength and ductility of the material were examined by subjecting a set of sheets to a certain number of CBT cycles under the optimized parameters and annealing. In doing so, strength of the material increased by a factor of 1.6 along the sheet softest direction, while by a factor of 1.3 along the sheet strongest direction reducing the anisotropy. Microstructural evolution was characterized using electron-backscattered diffraction, while texture evolution was measured using neutron diffraction. These results revealed slip dominated deformation with minor activity of twinning. The role of CBT in preserving integrity of the sheets to large plastic strains is discussed by comparing measured and simulated geometries and mechanical fields.
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. Measurements 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 investigated 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.
Crystallographic texture in metals influences material properties, e.g., r-value. In this work, a moderately strong texture is obtained in AA5182-O through continuous-bending-under-tension processing ...followed by a recovery heat treatment from the initial weak cube texture. EBSD scans confirm that the texture is retained after heat treating. The processed material exhibits increased strength and reduced planar anisotropy, providing benefits to subsequent forming operations, compared to the as-received material. Crystal plasticity simulations confirm the texture change during deformation and predict the flow stress response. Such simulations can be used for stress superposition process design to intentionally manipulate material properties.
Aluminum alloy (AA) 5182-O sheets are processed by continuous bending under tension (CBT) followed by heat treatment to investigate microstructural changes for optimizing strength and ductility of ...the alloy. Bending depth and pull speed parameters of the CBT process are optimized to enhance the achievable strain beyond a conventional uniaxial tension, by inducing significant microstructural changes in the sheets. CBT processed samples are subsequently heat treated at various time-temperature regimes to determine the best recovery condition. The combination of CBT and heat treatment effect on the mechanical properties is examined by the subsequent uniaxial tension experiment. Measured microstructural changes in terms of grain structure and texture by electron backscattered diffraction (EBSD) show that it is possible to change a 〈001〉 cube texture typically present in rolled and annealed AA sheets into a 〈111〉 fiber texture by combining CBT and annealing processing. Moreover, measured mechanical responses reveal that a particular combination of CBT and heat treatment at 270 °C for 2 h can increase strength by over 75 % at the expense of 37 % reduction of uniform ductility. Interestingly, only a complete recrystallization after CBT restores the r-value of as-received material, while the intermediate heat treatment conditions lower the r-value.
