Applied Mechanics and Materials Vols. 395-396

Abstract: The analysis of electrical erosion characteristics of contacts under DC load is conducive to the in-depth study of the arc erosion mechanism. Through the electrical contact experiment, the electrical erosion status of the Pt-Ir-Zr alloy under DC load of 25V/15A is studied in this paper. The results show that: the contacts have excellent anti-welding behavior and lower loss on arc ablation. The separation acceleration of the breaking process between the movable and static contacts is 154.32μm/ms2. The arc erosion surfaces of the material show a large number of paste-like coagulum and bubbles. There are some micro-cracks existing on the surface of the Pt-Ir-Zr alloy contacts. The obvious material transfer phenomenon occurs between the movable and static contacts under DC load.

Abstract: the behavior of internal oxidation of Ag-Cu-Zn alloy was studied at various internal oxidation temperatures for different internal oxidation time. The experimental results show that the short path diffusion, such as boundary diffusion and surface diffusion, is the main diffusion channel of oxygen in initial stage of oxidation, oxidation rate is fast, while the internal oxidation exponent n=1. Then the oxygen diffusion translated from short path diffusion into long path diffusion with the extending of internal oxidation time, and the oxidation rate was slowed down, while the internal oxidation exponent n=1.67. The action size is increased with the temperature increase. The diffusion activation energy of oxygen in initial stage of oxidation is lower than that in middle and late stage.

Abstract: In order to investigate the ratio of Zn/Y on as-cast Mg-4Zn-xY (x=1, 2, 3 in wt. %), microstructure and mechanical properties are analyzed by scanning electronic microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrum (EDS) and tensile testing. The results indicate that with the decrease of the ratio of Zn/Y, microstructures are refined more greatly and the spheroidization and uniformity coefficient are improved obviously, and the morphologies of second phases are changed from diversity to unity, resulting in an improvement of mechanical properties of alloys.

Abstract: Cu-10%Nb alloys were solidified with or without electromagnetic stirring. The effect of electromagnetic stirring (EMS) on the distribution of Nb particles in solidified Cu-10%Nb ingots and the performance of its deformed wires were studied. The 300A/16Hz EMS has refined the microstructure of Cu-10%Nb alloy, with smaller phase size and larger amount, and is benefit to the homogenous distribution of Nb-rich phases. The fitted lognormal distribution of Nb phase size in case without or with EMS is compared, and the EMS case has the higher frequency percentage in the range of smaller size for both the solidified ingot and the deformed wire. Cu-10%Nb wires in EMS case have a less value of electrical conductivity and a considerably higher ultimate tensile strength compared with that without EMS.

Abstract: Thermal flow finite element simulation was carried out to deeply understand the solidification and deformation phenomena of magnesium alloy in molten zone during twin-roll casting process. The results show that temperature near the nip of the rolls is about 680K based on current conditions, and there are two vortexes in the molten pool during casting, a peak formed at solidus. Due to the metal flows in molten pool and relative rotates of the rolls, temperature field of molten zone is different from normal casting, which will cause the solidification structure changes. An experiment by using a vertical type twin-roll caster was also conducted, and the amount of deformation bands at the joint line is larger than that at the two sides. Substructures can be found due to dynamic recrystallization during casting process.

Abstract: The paper had studied the property of corrosion resistance of AlCoCrTiNiCu_x high-entropy alloys by using the way of loss-weight. The results found that the function of corrosion resistance of Cr, Ni, and Ti is very good and the property of corrosion resistance of AlCoCrTiNiCu_x high-entropy alloys is reduced with increasing the content percentage of Cu, but the content percentage of chemical compounds on metal is increased.

Abstract: Microstructure evolution characteristics and the influence of the intial grain size on the dynamic recrystallization of AZ31 were investigated by rolling at deformation temperature of 280 °C, 30% reduction and strain rate of 5.6s^-1. The results indicate that under the present deformation condition, when the grain size is 6.2μm the dynamic recrystallization does not occur , twinning dynamic recrystallization (TDRX) occurs when the original grain size are of 7.9μm and 12.7μm, when the original grain size is 21.1μm rotating dynamic recrystallization (RDRX) occurs.

Abstract: this paper introduces the main parameters of the mining and arrival coal quality, and analyzes the low temperature oxidation characteristic of Indonesia coal through thermogravimetric test; meanwhile, the mechanism of spontaneous combustion of Indonesia coal is clarified, the advantages and disadvantages of various inflaming retarding methods are compared, and the development direction of inflaming retarding of Indonesia coal in the power plant is pointed out.

Abstract: The determination of the physical property cutoffs of the effective reservoirs is a major factor that affects the result of the reserve calculation and is a difficult problem in the research of the reservoir evaluation. It is related to the exploration, development and decision-making. This paper used the empirical statistical method, the minimum pore throat radius method, the oil attitude method and the porosity permeability cross plot method to exploratorily strike the physical property cutoffs of the effective reservoirs of Yaoyi Formation in Cha 48 zone. It was based on the actual situation of the data of cores, the well testing and the well logging and combined with the applicability of various methods. The results achieve the attest of the data from the well testing and the producing test and provide the basis for the reservoir calculation.

Abstract: The strain-controlled fatigue tests on extruded AZ31B magnesium alloy were conducted under the uniaxial loading with strain ratio Rε=-∞, frequency of 0.1 Hz and strain amplitude of 2% at room temperature. The cyclic hardening behavior was investigated. It was found that, during the low cycle fatigue (LCF) process, as the number of cycles increases, the stress amplitude increases corresponding to the decrease of the plastic strain amplitude. The development of dislocation density can be described as the function of the number of fatigue cycles, and the behavior can be explained well based on the dislocation density development model.