Modelling twinning evolution during plastic deformation in hexagonal close-packed metals

• A new model predicting twinning at a grain level is applied in several HCP metals.
• Adding size and orientation effects allows identifying grains with high twin fraction.
• Strain rate sensitivity of twin behaviour is controlled by dislocation mobility.
• Y effects in MgY are predicted allowing to design Mg alloys with higher ductility.

A new model describing the twin size and volume fraction evolution at the grain level is proposed. An evolution equation for the mean twin length on individual grains is expressed in terms of the local grain structure. This includes characterising the grain size and orientation distributions in the deformed specimen. Additionally, the twin volume fraction is predicted by computing the collective twin volume increments on each grain, if the grain structure is known. A twin nucleation-rate equation is proposed; it depends on dislocation activity, and the local twin and grain orientations. The model is applied to describe twinning behaviour in Be, Hf, Mg, Ti and Zr for various loading and texture conditions, including Y addition effects in MgY alloys. Twinning evolution is compared in Mg holding unimodal and bimodal grain size distributions.

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