Search

In order to evaluate the effect of secondary cold reduction rate on the drawing performance of double reduction tinplate and explain the mechanism, a detailed investigation into the microstructural characterization, dissolved carbon atoms, texture characterization by an X-ray powder diffractometer (XRD) and electron backscatter diffraction (EBSD), and earing behavior were carried out with different secondary cold reduction rates of 15%, 20% and 25% for double reduction tinplate. The experimental results indicate that 15% secondary cold reduction rate could obtain a better drawing performance because there are no holes and cracks at the microstructure, and the content of dissolved carbon atom is relatively low, at the same time, it has a better texture distribution and low earing coefficient.

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 simple process so-called forced convection stirring casting (FCSC) was proposed to prepare large-diameter 7075 Al alloy ingots. The flow behavior, temperature, and composition fields of the melt in the FCSC process were simulated. The macromorphology, macrosegregation, microstructure, and mechanical properties of the ingots prepared by the FCSC were studied and compared with those prepared by normal casting (NC). The results showed that in the FCS device, the strong convection caused by the axial flow and circular flow rapidly promoted the uniformity of the temperature and composition fields of the melt. Microstructures of the FCSC ingots from the edge to the center were all nearly spherical grains, which were much finer and more uniform than that of the NC ingots. The rotation speed played an important role in the microstructure of the FCSC ingots, and the grains became finer and rounder as the speed increasing. The FCSC process effectively eliminated cracks, improved macrosegregation, and decreased the eutectic phase area fraction and the average grain boundary thickness of ingots. Mechanical properties of the ingots prepared by the FCSC are far better than that of the NC ingots.

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.

An advanced rheomolder, equipped with a thin-walled phone cover mold, was introduced and used to manufacture the AZ91D magnesium alloy. Effects of different processing parameters including pouring temperature, cylinder temperature and injection velocity on the microstructure and mechanical properties were investigated. The results showed that, with the decrease of pouring temperature or the increase of injection velocity, the size of α1-Mg decreases while the sphericity increases, and the porosity fraction reduces, which raise mechanical properties of rheomolded AZ91D. As the cylinder temperature decreases, the size of α1-Mg decreases and the sphericity increases initially and then remains relatively unchanged while the solid fraction increases continuously. Also, the cylinder temperature has a significant effect on mechanical properties of rheomolded AZ91D and the highest mechanical property is obtained at a cylinder temperature of 555 °C. The optimal rheomolded AZ91D with tensile strength of 273 MPa and elongation of 7.2 % were obtained at the pouring temperature of 600 °C, injection velocity of 2.1 m/s and cylinder temperature of 555 °C. Compared with high pressure die-casting, the tensile strength and elongation were increased by 22.4 and 213 %, respectively.

The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC). A new machine, forced convection mixing (FCM) device, based on the mechanical stirring and convection mixing theory for the preparation of semisolid slurry in convenience and functionality was proposed to produce the automotive shock absorber part by R-HPDC process. The effect of barrel temperature and rotational speed of the device on the grain size and morphology of semi-solid slurry were extensively studied. In addition, flow behavior and temperature field of the melt in the FCM process was investigated combining computational fluid dynamics simulation. The results indicate that the microstructure and pore defects at different locations of R-HPDC casting have been greatly improved. The vigorous fluid convection in FCM process has changed the temperature field and composition distribution of conventional solidification. Appropriately increasing the rotational speed can lead to a uniform temperature filed sooner. The lower barrel temperature leads to a larger uniform degree of supercooling of the melt that benefits the promotion of nucleation rate. Both of them contribute to the decrease of the grain size and the roundness of grain morphology.

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.