Wang Aiqin

Hot Deformation Behavior and Processing Map of SiCp/2024Al Composite

Abstract The hot deformation behavior of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500D thermo-mechanical simulator at the temperatures ranging from 350∼500 °C under strain rates of 0.01∼10 s −1 . The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 153.251 kJ/mol. To demonstrate the potential workability, the stable zones and the instability zones in processing map were identified and verified through micrographs. Considering processing map and microstructure, the hot deformation should be carried out at the temperature of 450 °C and the strain rate of 1 s −1 .

Effects of Rare Earths on Toughness of 31Mn2SiRE Wear-Resistance Cast Steel

Abstract The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness ( a K) by 44%, yield strength (σ 8 ) by 10%, and elongation (δ 5 ) by 42%.

Hydrothermal Synthesis of Nano-sized Cupric Tungstate (VI) Dihydrate and Its Synthesis Mechanism

Copper nitrate and sodium tungstate were employed to prepare nano-sized cupric tungstate (VI) dihydrate (CuWO4·2H2O) by hydrothermal method. Formation processes of Cu2WO4(OH)2 precursors were discussed, and the synthesis mechanism of CuWO4·2H2O precipitates from Cu2WO4(OH)2 precursors during the process of hydrothermal reaction was established. Morphological and microstructural investigations of precursors and precipitates were carried out using high resolution transmission electron microscopy (HRTEM) and X-ray diffractometer (XRD). Results show that the synthetic products CuWO4·2H2O particles are mostly spherical in the size range from 20 to 30 nm. Transmission electron microscopy (TEM) observations indicate that the formation of CuWO4·2H2O follows in situ crystallization mechanism in the process of hydrothermal reaction. In the long term hydrothermal environment of high pressure and temperature, Cu2WO4(OH)2 precursors are surrounded by WO42- ions, which are adsorbed and diffused on the surface of Cu2WO4(OH)2. By dehydrations and molecular rearrangement, CuWO4·2H2O precipitates heterogeneously nucleate here. WO42- ions react with Cu2WO4(OH)2 through CuWO4·2H2O layer until WO42- ions have been depleted.

Effect of Sic Volume Fraction on Properties of Sic/6061 Composites

The SiC/6061 composites were produced by powder metallurgy method, with the SiC particle volume fraction being 20%, 25%, 30% respectively. The microstructures of the materials were observed by Optical Microscope. The tensile strength and Coefficient of thermal expansion (CTE) were examined. Turner and Kerner theoretical models were employed to analyse the CTE. The influences of the SiC particles volume fraction on the microstructures and performances were analyzed. The results show that with the increase of the SiC particles volume fraction in the composites, the clustering degree of the SiC particles increases in the matrix, and the CTE decreases which is close to the average of the Kerner and Turner theoretical model predictions, and the tensile strength increases but when the volume fraction of SiC particles exceeds the critical value of 30% the tensile strength of the composite decreases. And the strengthening mechanism of experimental materials was discussed.