Advanced Materials Research Vols. 295-297

Abstract: The effects of the low frequency electromagnetic field on the macrosegregation of the 7075 aluminum ingots were investigated. The 7075 aluminum ingots with the diameter of 200 mm were prepared by the conventional direct chill casting and the low frequency electromagnetic field casting (LFEC) processes, respectively. The temperature during casting at steady state was measured, and the mushy region was observed from the temperature contour. The concentrations of the alloying elements were measured by the spectrograph. It was found that the transition region was broadened, but the mushy zone became narrower with presence of the low frequency electromagnetic field. The centerline macrosegregation of the ingots was alleviated by the low frequency electromagnetic casting process.

Abstract: Cemented carbide tools are widely used in machining industry due to their superior properties. WC-Co composite cemented carbide tool materials reinforced with Ni and SiC nano particles were fabricated by using powder metallurgy followed by hot extrusion. Different modified mechanism (nano-SiCp modified，binder(Co, Ni) modified and Co electoless plating coated WC ) of WC-based cemented carbide tool materials were fabricated by using powder metallurgy followed by hot extrusion. Microstructure，mechanical and cutting properties were studied. The results show that the heat-resistance, as well as high-temperature behaviors (hardness, wear-resistance and obdurability ) ，can be improved by adding nano-SiCp on WC-based cemented carbide. Ni-Ti replaced Ni as binder can improve hardness and red-hardness of tool. Mechanical properties are enhanced due to Co as binder having more wettability on WC surface than Ni .

Abstract: The deformability of sheet metal drawing is influenced by many technology and die structure parameters. By orthogonal experiment, the main four factors effected the deformability of sheet metal drawing have been studied in the two-stage drawing respectively. The results have shown the influencing order and optimum parameters of key factors were varied in different multi-stage sheet metal drawing. The influencing order of the four factors in the first drawing was the blank-holder force > dies radius>the lubricants>the punch-nose radius. The second drawing was dies radius>the lubricants>the punch-nose radius >blank-holder force. The optimum technology and structure parameters have been also determined by the experiments in the paper.

Abstract: The microstructures and mechanical properties of the Mg-5Y-xMM alloys have been investigated, where MM stands for the Ce-rich misch metal. It was found that the additions of the MM led to refinement of the microstructures and improvement of the mechanical properties. The dynamic recrystallization has occurred during hot extrusion. As a result, the mechanical properties of the alloys were greatly improved after hot extrusion. It was indicated that the specimens of the extruded alloy Mg-5Y-3MM displayed a higher tensile strength, and the values of the ultimate tensile strength and yield tensile strength were 260 and 183MPa, respectively.

Abstract: In this paper, roll wear calculation model is developed considered the length of rolled strip, load distribution between rolls, roll surface roughness and other factors, and the corresponding calculation procedure has been developed. The experimental results show that the calculation value of the program is close to the actual data, and its accuracy can meet the requirement of on-line shape control. Based on the procedure, wear of each roll is calculated to study the effects of asymmetric bending. It is shown that asymmetric bending can decrease the local severe wear of rolls, and improve the uniform degree of roll wear distribution, thus the effects of asymmetric bending force on intermediate roll is better than that on work roll. Therefore asymmetric bending of intermediate roll can be used to reduce the wear of rolls in production.

Abstract: In order to obtain actual preferred principle of processing parameter about three-roller forward spinning of aluminium alloy tube, take the aluminium alloy tube that spun by Jiangyang chemical plant as a research object, based on nonlinear FEA software ANSYS/LS-DYNA, carried on 3D dynamic simulation, spinning force and stress-strain analysis to three-roller forward spinning of aluminium alloy tube under different processing parameter. Analysis results indicate: When feeds of spinning roller take 0.66mm/r~1.58mm/r(except 0.97mm/r), spinning force, component forces of spinning force, stress and strain have minimal change. Rounded angle radius of spinning roller should be greater than 60% and less than 125% blank thickness of aluminium alloy tube. Forming angle of spinning roller should take 22°~24°. Diameter of spinning roller should take 220mm~240mm. The conclusion has important meaning to further studies and actual manufacture about three-roller forward spinning of aluminium alloy tube.

Abstract: The paper deals with recrystallization conditions monitoring for MoNiCr nickel superalloy. The alloy is determined for modern concepts of nuclear reactors in which molten fluoride salts are used in the primary and/or secondary circuit as coolants. It represents a material with high corrosion resistance against fluoride salts and it has very good creep properties in the temperature range of interest for such a kind of reactors between 650 – 800 °C as well. The manufacture of vessels and fittings from MoNiCr alloy requires appropriate forming technology for this high-alloyed material. The key moment seems to be forming of the material cast state to the state of cast recrystallized microstructure with a homogenous fine grains. A kind of stress condition is besides temperature very important in the course of a hot forming of this type of hardly deformable materials. Forming with prevailing pressure state of stress increases probability that material can attain level of deformation allowing recovery and recrystallization processes without the material failure. Preceding cold deformation can essentially accelerate the recrystallization process. Investigation of forming condition influence on MoNiCr microstructure and thus its formability is performed here.

Abstract: The mechanism of dynamic instability of large span spatial structures under high wind speed should be studied carefully, but it has seldom been done before. In this paper, a double-layer cylindrical reticulated shell under a typical wind flow is taken as an example to study the dynamic instability of large span spatial structures under wind flows. The interaction of the shell and the flow is ignored and unsteady wind forces on the shell are obtained from wind tunnel tests. The dynamic instability status of the shell is determined by the Budiansky-Roth criterion. The results show that the double-layer cylindrical reticulated shell will become dynamically instable under high wind speed.

Abstract: PEM fuel cell is the most promising application as an automotive power. Proton transfer in PEM is one of important factors to understand the performance of PEM fuel cell. In this paper, the proton transfer mechanisms are analyzed by the molecular simulation based on the basic principle of molecular dynamics. Effects of water content in the proton exchange membrane and cell temperature on the proton transfer in the membrane are studied by the radial distribution function (RDF). Results show that proton transfers in the Nafion polymer by water bridges between two sulfonic groups of adjacent side chains. There are more water bridges supporting proton transfer with the increase of water content in membrane. The increase of cell temperature speeds up the form and break of O-H bond, which promotes the proton transfer. The research results are very helpful to understanding the proton transfer mechanism in proton exchange membrane and promoting the applications of PEM fuel cell.

Abstract: PZT thin film was prepared on platinized Si substrates by liquid-source mist microwave plasma enhanced chemical vapour deposition. Using citric amine and ethylene glycol as chelating agent, a homogeneous, stable water solvent sol was prepared successfully, which was suitable to develop PZT thin film by LSMPECVD. From the analysis of FTIR spectra, the special functions of chelating agents were identified. It shows that this deposition process is nonuniform nucleation, the PZT thin film grew with island model. Prior to fill the blank sites on the substrate, the latter deposited PZT congregated together to reduce surface energy. The morphology and structure were characterized by SEM and XRD analysis.