Advanced Materials Research Vols. 146-147

Abstract: Zn-Ni-Ti-O system ceramics were prepared by solid state reaction method using two different routes. The positive temperature coefficient of resistivity (PTCR) behavior and microstructure were investigated in terms of different composition and synthetic routes. It was found that using ZnO, NiO and TiO2 as the starting materials (route A), the prepared ceramics exhibited low room temperature resistivity (ρRT was ~102 Ω•cm) and inferior resistivity jump (ρmax/ρmin<50) starting at the temperature when it began to rise. However, using ZnOss (Zn0.95Ni0.05O), NiOss (Ni0.55Zn0.45O) and spinel phase (ZnNiTiO4) as starting materials (route B), the ceramics revealed ρRT >103 Ω•cm and marked resistivity jump (ρmax/ρmin was ~102) starting at ~200 °C. The microstructure showed that the ceramics prepared by route B possessed clear-cut grain boundaries but the grains of ceramics prepared by route A were irregular shape and distribution.

Abstract: A large scale ingot was dissected to study the segregation law of the elements. The influence of composition segregation to the microstructure and mechanical properties of SA508-3 steel was studied by the comparison of three positions on the ingot. Two precipitated phases were approved to be alloyed cementite and molybdenum carbide (Mo2C). It has demonstrated that the middle and upper parts of the ingot were almost the same in compositions except for a slightly difference in the carbon content. The upper part with more carbon included has relatively more carbide precipitation after the performance heat treatment. The bottom part of the ingot has the lowest carbon and molybdenum content, while the reduction in the amount of precipitated carbide was not observed. On the contrary, fine needle-like Mo2C are extensively distributed in the matrix of the bottom part besides a variety of coarse cementite rods. And the data of Energy Dispersion Spectrum (EDS) mapping has suggested that precipitation of Mo2C tends to bring the segregation of impurities. Many large inclusions were found in the bottom part of the ingot, which were considered to be the main reason for the strength loss of this area.

Abstract: An elevated temperature deformation test of industrial coarse-grained Ti-6Al-4V(TC4), which is for gas forming process, was conducted under the temperature of 880 ~ 980°C and the strain rate of 5×10-4mm/s, 1×10-3 mm /s, 5×10-3 mm /s, 1×10-2 mm /s. Based on the stress-strain curve of that material, the Johnson-Cook model, Exponential model, Series model, Parallel model and the Kumar model were established by using the regression analysis on stable deformation stage and whole strain stage (strain hardening stage plus stable deformation stage) respectively. The appropriate application circumstances of those models are analyzed. By using statistic analysis and aiming at minimizing the error rate between actual value and regression value, Kumar model is selected as the constitutive model of that material for gas forming test. Based on Kumar model, the industrial coarse-grained TC4 gas forming test was simulated by nonlinear finite element software Msc.Marc. The simulation results agree well with the actual parts. The Kumar model was appropriate and accurate.

Abstract: A life cycle assessment was carried out to estimate the environmental and economic impacts of recycled aluminum alloy production. The impact seen from non-carcinogens, respiratory inorganics, terrestrial ecotoxicity, global warming and non-renewable energy categories played an important role to overall environmental impacts. The impact seen from carcinogens and aquatic ecotoxicity played relatively small role, while the impact seen from the rest categories affect the environment was ignorable. Specifically, the emissions from the aluminum and silicon production stages involved played an important role due to high energy consumption, while potential impact generated from other elements was quite small. Similarly, the cost of old aluminum scrap represented the dominant contribution to overall economic impacts. Accordingly, choosing natural gas based electricity production technology and improving old aluminum scrap consumption efficiency are the efficient way to minimize the overall environmental and economic impact, respectively.

Abstract: Based on momentum theorem, principle of mass conservation, and some experimental formulas, the distribution of velocity in ladle furnace was calculated by CFD methods. Blowing argon arrangement in ladle furnace is researched, through comparing 13 schemes about blowing argon arrangement, some conclusions are obtained. When there is only a blowing argon in ladle furnace, the better scheme is that the distance from center of LF bottom to the hole is 0.7r. When there are two blowing argon in ladle furnace, the better scheme is that the angle of two holes is 60°~90°and distance from center to blowing argon hole is 0.5r~0.7r.

Abstract: Curing is the key to the bonding, the study indicate that: curing effect on the glue bond strength, formaldehyde emission as well as Productive Efficiency; the better curing system can ensure the Productive Efficiency in basic to decrease the FE. This paper considered the production practice, studied the curing properties of different MUF resin with TGA. The experimental result: Different curing systems, made different curing process. For A curing system, curing rate is the fastest, the degree of curing is best. Cured stability is well. While in the C curing system, Because of their poor degree of cross-linking, poly-condensation cross-linked imperfect. While, Along with the increasing of n(F):n(U1), initial decomposition temperature increased, the maximum rate of mass loss moved to higher temperature, mass loss declined, decomposition activation energy increases, aging resistance increased.

Abstract: The characteristic parameters of electrochemical noise (EN) spectra were used to study the corrosion process of aluminum alloy in distilled water with or without chlorate (Cl-).The experimental results showed that the parameters obtained from the time-domain spectra analysis were not consistent with the parameters obtained from the frequency-domain analysis. This paper attempted to explain the phenomenon by the time-domain noise spectra, the corrosion characteristic of aluminum alloy, the source of noise transient, and the types of the pitting corrosion of aluminum alloy.

Abstract: The acoustic properties of aluminum foams by gas injection method were studied experimentally. The micro and macro structure of aluminum foam with closed cells were observed by optical microscope (OM) and scanning electron microscope (SEM). The special structure of the closed-pores of the aluminum foams have leaded to good performance of the sound absorption based on three mechanisms: Helmholtz resonance, cell wall vibration and viscous and thermal effects. The effect of cell sizes, thickness of aluminum foams has been investigated and the cavity set at the back of the foam samples on the sound absorption efficiency of the foams has been measured. Analytical models of membrane vibrations were used to explain the sound absorption capacity of the foams.

Abstract: The prediction of dynamic recrystallization (DRX) plays an important role in design of hot forging process. In this work, a simulation model coupled cellular automaton (CA) with FEM was proposed to quantitatively simulate the microstructure evolution and flow stress during 7050 aluminium alloy wheel die forging. The model of dislocation density was established by isothermal compression test on Gleeble-1500. The physical fields, such as temperature, strain rate and strain, were obtained by DEFORM-3D for microstructure simulation. To refine grain size and improve uniformity, the isothermal forging parameters for 7050 aluminium alloy wheel were optimized by CA simulation. The simulation results showed that DRX percentage increased from 9.9% to 50% by using isothermal forging instead of hot die forging, while the flow stress decreased from 84MPa to 40MPa. Uniform density and small grain related with high mechanical properties were achieved via isothermal die forging process. The experiments of scaled wheel die forging were carried out on a hydraulic press with nominal working pressure 3150KN to verify simulation results. The good agreement between the simulation results and the experimental results indicate that the simulation model presented in this work can be used to predict the microstructure evolution of forging and optimization of forging process.

Abstract: Polyphenols in methanolic extracts from Sonneratia caseolaris seeds were determined by HPLC coupled with electrospray mass spectrometry and quantified by HPLC coupled with ultraviolet/visible detection in order to evaluate their stability of the extracts during 6 months of storage. Antioxidant activity was measured by using TEAC assay, and the free radical scavenging activity was monitored in the initial 3 months of the stability evaluation. Study on the effect of temperature on the stability of the methanolic extract indicated that gallic acid, luteolin-7-O-glucoside, and luteolin were unstable at 25 and 45°C during storage time. At -80 and 4°C the quantities of luteolin-7-O-glucoside reduced while those of luteolin increased at the same time. The results suggested that luteolin-7-O-glucoside was hydrolyzed to luteolin. Therefore the polyphenols should be kept at low temperature. Antioxidant activity of methanolic extract was preserved in all temperatures during the first 3 months.