Rheological properties of metal alloys in the semi-solid state

AbstractThis paper reviews the information published and constructs rheological equations for semisolid metals. For materials having a volume fraction solid (Φ) less than about 0.6, the solid-liquid suspension can be described by the model first proposed by Bingham. The fluid has a finite yield stress, which, in semisolid Al-Si alloys, may be represented by the equationτ = 9615 · Φ3/Φm−Φwhere τ0 is in Pascals, and Φm is the maximum packing fraction of spherical solid grains and is numerically equal to 0.6. The yield stress accounts for more than 90% of the total shear stress in most semi-solid metals. The Bingham viscosity makes a minor contribution at normal strain rates. At solid fractions greater than about 0.6 the grains form a coherent skeleton or network. A theoretical approach first applied to porous powdered metals is used to describe the deformation of these materials. The deformation is defined by a reduced flow stress, σ = τmushy/τ solid, at the temperature under consideration. For conditions u...