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A new and effective semisolid slurry preparation process with air-cooled stirring rod (ACSR) is reported, in which the compressed air is constantly injected into the inner cavity of a stirring rod to cool the melt. The slurry of a newly developed high thermal conductivity Al-8Si alloy was prepared, and thin-wall heat dissipation shells were produced by the ACSR process combined with a HPDC machine. The effects of the air flow on the morphology of α1-Al particles, mechanical properties and thermal conductivity of rheo-HPDC samples were studied. The results show that the excellent slurry of the alloy could be obtained with the air flow exceeding 3 L/s. Rheo-HPDC samples that were produced with the air flow of 5 L/s had the maximum UTS, YS, elongation, hardness and thermal conductivity of 261 MPa, 124 MPa, 4.9%, HV 99 and 153 W/(m·K), respectively. Rheo-HPDC samples show improved properties compared to those formed by HPDC, and the increasing rates of UTS, YS, elongation, hardness and thermal conductivity were 20%, 15%, 88%, 13% and 10%, respectively.

A simplified process, namely forced convection stirring (FCS), was proposed to prepare four different semisolid slurries of Al and Mg alloys. A simple rheological high pressure die-casting (Rheo-HPDC) process was developed by combining the FCS device with a HPDC machine. The temperature and composition fields of the melt in the FCS process were simulated. The microstructures and mechanical properties of the alloys formed by the FCS Rheo-HPDC were studied and compared with those formed by HPDC and other Rheo-HPDC processes. The results showed that the FCS process can prepare slurries in which the primary particles are fine, spherical and uniformly distributed in the matrix and the process can effectively suppress macrosegregation. The strong convection rapidly promotes the uniformity of the temperature and composition of the melt. Compared to HPDC and other Rheo-HPDC alloys, the alloys formed by FCS Rheo-HPDC have an improved ultimate tensile strength, yield strength, elongation and hardness, due to the refinement of microstructure and the decrease of porosity. Heat treatments can be utilized to further enhance the mechanical properties of FCS Rheo-HPDC alloys.

An advanced rheomoulder, which is a device in the integration of melting metal, storage, slurry preparation, transportation and injection forming, was introduced and used to manufacture rheomoulding AZ91D alloy. Effects of pouring temperature and cylinder temperature on microstructures and mechanical properties of rheomoulding AZ91D alloy were investigated. The results show that the process can obtain such rheomoulding AZ91D in which primary α-Mg particles are fine, spherical and uniformly distributed in the matrix. With the decrease of pouring temperature, the morphology of primary α-Mg particles changes from coarse rosette-like to fine spherical shape gradually. As the cylinder temperature decreases, the average size of primary α-Mg particles decreases firstly and then substantially maintains stable while the sphericity and solid fraction increase continuously. Also, decreasing pouring temperature or cylinder temperature properly contributes to improving mechanical properties of rheomoulding AZ91D for the refinement of α-Mg particles and the decrease of porosity fraction. Furthermore, rheomoulding AZ91D performs much better than thixomoulding, rheo-diecasting and high pressure die-casting (HPDC) in terms of mechanical properties. Compared with HPDC, the tensile strength, yield strength and elongation are increased by 27.8%, 15.7% and 121%, respectively.

A self-developed forced convection rheoforming (FCR) machine for the preparation of light alloy semisolid slurry was introduced. The microstructure characteristics of 7075 aluminium alloy semisolid slurry at different stirring speeds prepared by the FCR process were analyzed. The experimental results suggest that with the increase of the stirring speed, the mean grain size of the semisolid decreases and the shape factor as well as the number of primary grains increase. Meanwhile, the preparation process of semisolid slurry was numerically simulated. The flow characteristics of the melt in the device and the effect of the stirring speed on temperature field and solid fraction of the melt were investigated. The simulated results show that during the preparation process of semisolid slurry, there is a complex convection within the FCR device that obviously changes the temperature field distribution and solid fraction of the melt. When the convection intensity increases, the scope of the undercooling gradient of the melt is reduced and temperature distribution is improved.