Due to the high stacking fault energy of pure aluminum and the prediction that trailing partial dislocations were energetically favoured over twinning partials, it was believed that twinning normally does not happen in Al, except at crack tips. Using molecular dynamics simulations, deformation twinning in single crystal Al was demonstrated, where a shear strain was applied parallel to (111) and along [1¯21]. Based upon the simulations, a partial dislocation reaction model was proposed that generates a two-layer twin embryo as one mechanism for twin nucleation after the emission of the trailing partials. The conditions favourable to twin nucleation in terms of the effective stacking fault energy were also analyzed. These analyses shed light on the observations of deformation twins nucleated in Al, especially those in nanocrystalline grains. Experimental observations of deformation twins in pure Al after high-strain-rate shear at room temperature were also presented.

A Nucleation Mechanism of Deformation Twins in Pure Aluminum. B.Li, B.Y.Cao, K.T.Ramesh, E.Ma: Acta Materialia, 2009, 57[15], 4500-7