An experimental investigation was made into the dependence of deformation twinning in AZ31 upon various aspects of plastic deformation, including the anisotropic strain-hardening rates, the tension/compression yield asymmetry, and the evolution of crystallographic texture. It was seen that AZ31 exhibited unusually high normalized strain-hardening rates compared to α-Ti that occurred beyond the strain levels where extension twins have completely altered the underlying texture. This observation challenges the validity of the generally accepted notion in the current literature that the high strain-hardening rates in AZ31 were directly caused by extension twins. It was postulated here that the thin contraction twins were very effective in strain hardening of the alloy by restricting the slip length associated with pyramidal <c+a> slip. This new hypothesis was able to explain the major experimental observations made in this study and in the prior literature. A new hypothesis was also presented for the physical origin of observed differences in the thicknesses of extension and contraction twins. The stress fields in selected matrix–twin configurations were modelled using crystal plasticity finite element models. The contraction twin, (0¯1•1)[0¯1•¯2], was predicted to form an internal extension twin, (01•2)[0¯1•1]; resulting in the commonly observed so-called double-twin sequence. The extension twin was suggested to inhibit thickening of this double twin by loss of twin-matrix coherency. Extension twins were predicted to retain their coherency and thus thicken.

Deformation Twinning in AZ31: Influence on Strain Hardening and Texture Evolution. M.Knezevic, A.Levinson, R.Harris, R.K.Mishra, R.D.Doherty, S.R.Kalidindi: Acta Materialia, 2010, 58[19], 6230-42