Effects Of Injection Velocity On Distribution Of Primary Alpha-Phase Particles In Semi-Solid High Pressure Die Casting Of Jis Ac4ch Aluminum Alloy

We have previously developed a new injection process with improved fluidity through applying shear stress. In this process, the product is made by injecting a solid-liquid slurry. Therefore, the microstructure of products made by this semi-solid injection process shows the dispersal of the spherical primary alpha-phase particles in the matrix. The primary alpha-phase particles and matrix are formed from the solid phase and liquid phase, respectively, when the slurry is injected. These phases have different properties, and the properties of semi-solid products are thought depend on the distribution of the primary alpha-phase particles. For this reason, semi-solid products have characteristic microstructures.In the present study, the distribution of primary alpha-phase particles was investigated in fluidity test specimens made of JIS AC4CH aluminum alloy, formed in a spiral cavity at various injection speeds. The number of primary alpha-phase particles at the edge of the specimens was higher than for other observation points. The primary alpha-phase particles were distributed homogeneously on the plane perpendicular to the flow direction at the edge of the specimens. In specimens formed at high injection speeds, at the observation points from the gate to the middle of the flow length, the primary alpha-phase particles were concentrated at the central axis of the flow direction. However, in specimens formed at low injection speeds, the primary alpha-phase particles were also distributed homogeneously in these areas. The concentration of the primary alpha-phase particles around the central axis was affected by the flow velocity in the cavity. These results suggest that the distribution of the primary alpha-phase can be controlled by changing the flow velocity.