Influence of barium addition on the microstructure and the rheological behaviour of partially solidified Al–Cu alloys

The effect of a barium addition to Al–Cu alloys on the morphology of liquid films in the mushy zone has been studied. It is shown that barium improves wetting of the solid phase by the liquid and thus, delays coalescence of the grains. In addition, tensile and shear tests have been carried out during solidification to determine the influence of Ba on the mechanical behaviour of the mush. It is observed that the fracture stress in tension is affected by the presence of Ba at the very end of solidification whereas an effect of Ba is not detectable in shear. It is proposed that this is due to delayed coalescence for Ba-treated alloys for which liquid films embrittle the alloy in tension up to very high solid fractions.