INFLUENCE OF THE PRIMARY SOLIDIFICATION ON THE SECONDARY SOLIDIFICATION DURING SEMISOLID METAL (SSM) PROCESSING OF A۳۵۶.۰ ALUMINUM ALLOY BY MECHANICAL STIRRING

Abstract:   The aims of this research were to investigate the effects of semisolid metal (SSM) processing parameters (i.e., shear rates –times – temperatures combinations) on the primary solidification products and isothermal holding duration, subsequent to cessation of stirring on the secondary solidification of Al-Si (A۳۵۶) alloy.   The dendrite fragmentation was found to be the governing mechanism of the primary dendritic to non-dendritic transformation, via rosette to final pseudo-spherical shapes during the primary solidification The secondary solidification of the liquid in the slurry was not only a growth phenomenon but also promoted by ۱) fresh heterogeneous nucleation and growth of dendrites and ۲) the dendritic growth of the primary solidification products in the remaining liquid. Upon cessation of stirring and gradual disappearance of the prior shear force, the slurry relaxed, and the secondary solidification products pertained to conventional solidification condition