Applied Mechanics and Materials Vols. 633-634

Abstract: Six devices based on tris [2-(benzo [b] thiophen-2-yl) pyridinato-C³,N] iridium Ir (btpy)₃ at the different concentration (0.5, 2, 8 and 12 wt. %) and in three host materials (PVK blending with PBD, PVK and CBP) were fabricated by spin-casting technique. The PL emission of Ir (btpy)₃ in solid film peaked at 594 nm. HOMO and LUMO energy levels were-5.08 and-2.67 eV. The EL peaks kept constant at 600 and 649 nm, and Commission International de L′Eclairage (CIE) coordinates were stable at (0.63, 0.36). With the increasing of doping concentration luminances were enhanced at the given voltage. Devices of host PVK blending with PBD exhibited much higher luminance than device in host PVK or CBP at the same concentration of 8 %. All devices exhibited strong red electrophosphorescence. The transport of electron and hole was balanced and energy transfer from the host to the guest complex was efficient. The characteristics of devices demonstrated that Ir (btpy)₃ was an excellent red emitter suitable for OLEDs.

Abstract: The effect of online solution and subsequent age heat treatment on microstructure and mechanical properties of die-cast AZ91D +1wt. %RE alloy were researched. The results indicated that online solution heat treatment led to inhibit some β-Mg₁₇Al₁₂ phase precipitation, and remained the Al element in matrix plays a role of solid solution strengthening. The online solution samples were aged at 160°C, 180°Cand 200°C. Microstructure results suggested that age treatment caused some lamellar β-Mg₁₇Al₁₂ phases precipitated near grain boundaries. The tensile properties of samples under air cool, online solution and subsequent age heat treatment were tested, which UTS were 194 MPa, 243 MPa and 244 MPa, and the elongation were 3.67%, 3.97% and 1.6%, respectively. The results indicated that the online solution could enhance the mechanical properties significantly, which the subsequent age heat treatment could not improve.

Abstract: Anti-extrusion process for the cylinder of spray-formed ultra-high strength aluminum alloy is researched in this paper. The spray-formed 7xxx aluminum alloy is treated by a two-step homogenization treatment (440 °C / 12h + 472 °C / 24h) after hot isostatic pressing (HIP), and then hot compression tests are carried out for getting the stress-strain relationship under different forming conditions. Anti-extrusion process for the cylinder is improved including changing the shape of mould and billet, and numerical simulation is used for researching the anti-extrusion process. According to the distribution of strain-effective, it can be seen that the improved scheme of anti-extrusion process can get more deformation than the common scheme at the bottom. The result of anti-extrusion experiments shows that the microstructure is evenly distributed across the cylinder under the improved scheme.

Abstract: The hot deformation behavior of Mg-7Gd-5Y-1Nd-0.5Zr alloy was investigated by compression tests at temperatures of 673 K, 713 K, 753 K, and 793 K and strain rates of 0.001 s^-1, 0.01 s^-1, 0.1 s^-1, and 1s^-1. The stress-strain curves exhibit typical dynamic recrystallization behavior with a single peak stress followed by a gradual fall toward a steady-state stress. The apparent activation energy of deformation and constitutive equations for the alloy were determined through regression analysis for conventional hyperbolic sine equation. The apparent activation energy of DRX and dynamic kinetics model for alloy were determined using the regression analysis for Avrami equation. Optical microscope and electron backscattered diffraction were employed to investigate the microstructure evolution of Mg-7Gd-5Y-1Nd-0.5Zr alloy during hot compression. The results suggested that the grain boundary is the main nucleation sites of dynamic recrystallization, and (0001) basal fiber texture has formed during hot compression.

Abstract: Based on the direct reduction alloying theory, experiments on chromium molybdenum alloy prepared through the direct reduction and alloying reactions between the high-carbon ferrochrome and molybdenum oxide were conducted in a laboratory scale. The critical factors that would impact the reduction rate of molybdenum oxide and the yield rate of molybdenum were analyzed. The results indicate that the reduction rate of molybdenum oxide can exceed 90%, meanwhile, the yield rate of molybdenum is affected by many factors and fluctuates in a wide range. As temperature rising, the reduction rate of molybdenum oxide is increased whereas the yield rate of molybdenum is decreased. With the amount of molybdenum oxide added increasing, the reduction rate of molybdenum oxide and yield rate of molybdenum are decreased simultaneously. Making slag during melting process and molybdenum oxide roasted by addition of lime are effective measures to improve the yield rate of molybdenum.

Abstract: Multi-axial forging was employed to produce simultaneously ultrafine grain size and weak texture in an Mg-7Gd-5Y-1Nd-0.5Zr alloy. The results indicate that the structure of fine grain size and weak texture could be achieved after two cycles of multi-axial forging, which leads to a substantial mechanical properties improvement. The grain refinement mechanism and texture evolution of Mg-7Gd-5Y-1Nd-0.5Zr alloy during multi-axial forging have been investigated.

Abstract: The composition, microstructure and Tafel polarization curve of the coating layer in hot-dipping Zn-0.2%Mn alloy bath have been investigated through XRF, SEM and electrochemical workstation. It is found that Mn is unevenly distributed in the coating layer. It shows that Mn is mainly distributed in coating outside surface. It is also means that Mn is tend to combine with Fe, O other than with Zn. Tafel polarization curve were collected by using three electrode system, Tafel polarization curve shows the electrochemical corrosion performance on internal surface is worse than the outside surface of coating layer, in 3.5% NaCl solution. It also means Mn enrichment and oxidation on the outside surface of the coating layer have an obvious influence to its corrosion performance.

Abstract: The hydrogen contents of molten aluminum solidifying in various molds were tested by the use of the G4 Phoenix DH and the samples of microstructure were analyzed under the optical microscope (OM). The results show that the hydrogen contents of solid aluminum decreases with the decreasing cooling rate. However, when molten aluminum solidifies in the adiabatic mold, the hydrogen content has a slight increase because of long time of exposure to the air. In addition, the microstructure of casting pure aluminum is refined with increasing cooling rate.

Abstract: The creep properties and microstructures of the aged (220°C, 6h) EW75 magnesium alloy at different temperature and of stress conditions were studied. The experimental results show that, the deformation temperature and deformation rate have visible influence on flow stress curve of EW75 alloy. When the deformation temperature was constant, the stress rheological increases with the strain rate increasing. When the deformation rate was constant, the flow stress decreases with the deformation temperature increasing. When the deformation temperature was low or deformation rate was quickly, the shear fracture was along 45° direction. At low temperature and high strain rate conditions, the recrystallization of EW75 alloy was not obvious. When raising the temperature and decreasing deformation rate, the dynamic recrystallization ratio was improved markedly. The generating and moving of dislocations during deformation were main factor to determine the final microstructures. At 100MPa, 200°C conditions, the creep rate control mechanism of EW75 alloy was dislocation slip by solute drag. Precipitation phases coarsening was the main reason that the creep properties of EW75 alloy decreased.

Abstract: In order to improve performance of Al-Sn bearing alloys, a new Al₂O₃/Al-Sn composite was fabricated through in-situ reaction between Al and SiO₂. A study has been conducted to investigate tribological performance of the composite on MMW-1 Computer controlled vertical universal friction and wear testing machine. The results show that Al₂O₃ and Si particles are mainly distributed in the grain boundary and particles are often coated by a thin Sn layer. Friction coefficient of Al₂O₃/Al-Sn composites is decreased with Sn additions up to 21wt. %.