Microstructure and Simulation of Semisolid Aluminum Alloy Castings in the Process of Stirring Integrated Transfer-Heat (SIT) with Water Cooling

The continuing quest for aluminum castings with fewer defects has aroused the interest in rheological high-pressure die casting (RHPDC). A new machine, stirring integrated transfer-heat (SIT) device, based on the mechanical stirring and enhanced cooling for semisolid slurry preparation was proposed to produce the thin-walled communication shell part by RHPDC process. The influence of SIT process characteristics on the microstructure was studied. The microstructure of SIT-RHPDC shell part in different locations was investigated. Combined with simulation, the flow characteristics and the temperature field change in the melt under the stirring-only process and different stirring with internal water-cooling conditions were studied to get a better understanding of the nucleation, grain growth and solidification behavior. Under the dual action of agitation and heat dissipation in SIT device, the fluid convection has changed the temperature field of the melt significantly. The temperature field of the melt becomes relatively uniform from a great temperature gradient and the continuous cooling rate is increased to 5 °C/s. In the same time, the slurry has a greater supercooling degree, and flows more evenly in the filling process. The experimental results indicate that compared with microstructure of an HPDC component, the microstructure at different locations of SIT-RHPDC part is composed of refined rosiness and nearly spherical particles.