Abstract
We have already developed a new injection process with improved fluidity by applying shear stress to date. In this process, the product is made by the injection of solid-liquid coexistence slurry. Therefore, the microstructure of products made by this semi-solid injection process shows the dispersal of spherical primary α-phase particles in the matrix. The primary α-phase particles and matrix are thought to have been the solid phase and liquid phase respectively when the slurry was injected. These phases have different properties, hence the properties of semisolid products are thought to vary according to the distribution of primary α-phase particles. For this reason, semi-solid products have a specific microstructure.
In this study, the distribution of primary α-phase particles was investigated in flow length test specimens made of AC4CH aluminum alloy formed in a spiral-shaped cavity at various injection speeds. It is found that the number of primary α-phase particles at the edge of the specimens is higher than other observation points. Also the primary α-phase particles were distributed homogeneously on the plane perpendicular to the flow direction at the edge of the specimens. At the observation points ranging from the gate to the middle of the flow length, the primary α-phase particles were found to concentrate on the center axis of the flow direction of specimens formed at high injection speeds. On the other hand, in the case of low injection speed specimens, the primary α-phase particles were also distributed homogeneously in these areas. The degree of concentration of the primary α-phase particles at the center axis is thought to be affected by the flow velocity in the cavity. These results suggest the possibility of controlling the distribution of the primary α-phase by changing flow velocity.
