Factors influencing ductility during cyclic torsional deformation of high purity aluminium

Abstract

Cyclic torsion (twisting in a forward clockwise direction followed by twisting in the reverse direction) of high purity AI wires under the simultaneous application of a small tensile load (P) was found to increase the torsional ductility considerably. The number of twists in each direction (N) varied between 5 and 50 and P ranged between 0.1 and 0.78 kg mm -2 . The average shear strain (~) increased considerably as N and/or P decreased. Specimens with a fine grain size showed higher ductility than those with a coarse grain size. By suitable combination of N, P and grain size, ~ exceeding 3000%, indicating superplastic behaviour, was obtained. The accompanying electrical resistivity changes were small and did not exceed 1%. The results are discussed in terms of recovery mechanisms and possible dislocation interactions occurring during this complex mode of deformation.