The predicted strengthening effect of precipitates of different shape and habit upon the basal, prismatic and {10•2} twinning deformation systems in magnesium was calculated. In parent material, rod precipitates parallel to the c-axis were predicted to be more effective than plates parallel to the basal plane in hardening the basal and prismatic slip systems. However, in twinned material, non-sheared basal plates were highly effective in inhibiting the basal slip necessary to relieve incompatibility stresses. The predictions suggested that basal plates would reduce asymmetry in strongly textured extrusions by preferentially hardening against twin growth compared to prismatic slip, whereas c-axis rods could have the opposite effect. The predictions were compared with the measured asymmetry for two magnesium alloys that form either c-axis rods (Z5) or basal plates (AZ91). In agreement with the model, it was shown that precipitation in Z5 led to an increase in asymmetry, whereas in AZ91 precipitation reduces asymmetry. These results suggested that tailored precipitation could be a useful tool for reducing asymmetry in wrought magnesium alloys.

Effect of Precipitate Shape on Slip and Twinning in Magnesium Alloys. J.D.Robson, N.Stanford, M.R.Barnett: Acta Materialia, 2011, 59[5], 1945-56