Deformation twinning in Al-4.8 wt% Mg

Deformation twins have been observed in polycrystalline Al-4.8 wt% Mg shock-loaded at -180°C to 13 GPa. Selected area diffraction confirms the twinning plane to be the {111}, similar to deformation twinning in other face-centered cubic (f.c.c.) metals. Transmission electron microscope (TEM) observations indicate that twins form preferentially near grain boundaries. A qualitative estimate of twin boundary velocity based on TEM observations suggests that twins in Al-4.8 wt% Mg form at speeds just below the shear wave velocity. Similarly shock-loaded experiments on 99.99 Al and 6061-T6 exhibited no evidence of deformation twinning. Substructure evolution and twin formation and/or lack of deformation twinning in the three aluminum alloys studied are discussed in terms of deformation twinning mechanisms.