Applied Mechanics and Materials Vols. 152-154

Abstract: The method of electric contact heating for nodular cast iron was based on the application of the contact resistance heating between the electrode and work piece to change the characteristics of the surface. The effects of processing parameters on the width and depth of modified layer were analyzed, and among the experimental factors, the electric current had the largest effect than the others. Optical microscope was used to describe the microstructure transformation and identify the phases in the modified layer. Results showed that a cementite-martensite microstructure in the melted zone and a martensite-ledeburite-ferrite microstructure with graphite nodules in the hardened zone have been observed; especially two typical hardened shells around graphite are achieved in the hardened zone, which are ledebruite-martensite shell and single martensite shell around graphite. The effects of the changed microstructures were additionally verified by microhardness measurements in the modified zone. The microhardness of the nodular cast iron was found to be significantly increased after electric contact heating.

Abstract: The influence of deformation conditions on the microstructure and texture evolution during hot compression of Mg-3Sn-2Ca (TX32) has been studied. Cylindrical samples were compressed uniaxially at different combinations of temperatures and strain rates in the ranges 300-500 oC and 0.0003-10 s^-1. The crystallographic orientation information of the as-cast and deformed specimens was obtained by EBSD micro-texture analysis. Activation of different slip systems was investigated using Schmid factor analysis and the results reinforce the importance of non-basal slip for deformation at high temperatures. Samples deformed at 500 oC/0.1 s^-1 resulted in a fully recrystallized microstructure with near random crystallographic texture.

Abstract: The microstructures and properties of AlSi7Mg alloy extruded at 575°C in semi-solid state were studied for analyzing the extruding feasibility of the casting aluminum alloy in high solid fraction. The results show that the microstructure of AlSi7Mg alloy through low-superheat direct chill (DC) casting mainly consists of the homogeneous, fine rosette-shaped grains. The microstructure of the billet reheated at 575°C in 15min is composed of stable and near- spherical grains, which are suitable for thixoforming in high solid fraction. Extruded at 575°C in the semi-solid state, the facial-smoothed parts of AlSi7Mg alloy with homogeneous, fine microstructure across the section is obtained, and the properties of extruded part are improved obviously.

Abstract: A non-traditional processing cycle for sheet-metal working based on the computerized image processing techniques is proposed. This novel system enables the effective fabrication cycle that realizes automatic inspection, quick delivery, and cost reduction.

Abstract: Based on the empirical electron theory of solids and molecules(EET) and valence electron theory of composition design of alloy, the valence electron structure(VES) of phases and phase interfaces of ZL203 are calculated in this paper, and the relationship between the VESs and mechanical properties are also studied. The results are as followed: 1) The of GP is bigger than of a, in other words, the resistance of dislocation movement in GP zone is bigger than that of in a matrix. 2) Compared with a matrix, the phases of q¢¢、q¢、q all have strengthening effects. From the bond combination of atoms composed in the strengthening phase of view, the strengthening effect of q is the best, that of q¢ is second, that of q¢¢ is the worst. 3) The precipitation sequence determined by n_A is well accordance with that of depended on thermodynamics free energy. 4) The electron density difference Dr of a/GP, a/q" and a/q¢ interfaces increases one by one, and the stress of these interfaces also increases one by one, therefore the strength falls down one by one. 5) Combined with FSFs and ICFs, we can deduce that the best aging stage of ZL203 is the end of the precipitation of q¢¢ and the beginning of the precipitation of q¢.

Abstract: Based on the polytypism transition temperature(PPT) of pure titanium, the the empirical electron theory of solids and molecules(EET) and the basic theory of the phase transformation of titanium alloys, a new method to calculate the PTT of titanium alloys is put forward after calculating the valence electron structure(VES) parameter nA which is the covalence electron pairs on the strongest bond of alloy phases, the crystal cell weight of  and  phases in the structure, the compensation coefficient of the phase and the temperature coefficient of  stable element. After calculating the PTT of some common titanium alloys, we find that the theoretical values are consistent with the experimental ones, so it is feasible to calculate the polytypism transition temperature of the titanium alloys on the covalence electron level.

Abstract: Fe₂O₃/attapulgite desulfurizer was prepared by impregnation, and was regenerated by use of heat air method. The desulfurization test from a gas containing 100 vol% H₂S was carried out over attapulgite supported Fe₂O₃ in a fixed-bed system at atmospheric pressure and room. The effects of the chemical nature of Fe₂O₃ on desulfurization capacity were studied. Materials before and after the desulfurization test were characterized using FTIR and XRD. Materials after the regeneration test were characterized using XRD. The characterization results suggest that modification process does not change the structure of attapulgite. Iron species disperses inside channels and the outside surface in the crystalline phase of iron oxide. The material with iron oxide content of 40.0 wt% presented highest H₂S uptake capacity. The deactivated that Fe₂O₃/attapulgite desulfurizer was regenerated 0.8L/min hot air in 323k, the regeneration efficiency reached 81.22%, by 4 times after regeneration can reach 51.9%.

Abstract: A study of chemical and structural characterization of fused fluxes for submerged-arc welding was conducted. Two flux formulations were prepared using mineral oxides for fusing processes. The micro-morphology and chemical composition of fused flux was compared by using the methods of Chemical analysis and scanning electron microscope (SEM)/Energy Disperse Spectroscopy (EDS) analysis. The phases of two fluxes were analyzed by X-ray diffraction (XRD) to determinate type of amorphous formed. This kind of flux characterization enables us to quantify the ions that might be present in the plasma arc during the submerged welding process due to the fluxes. This analysis is also possible the prediction of reactions in the weld pool.

Abstract: Uniaxial tensile deformation behavior of 7075-T6 under three different strain rates (0.001, 0.004 and 0.03s^-1) and five different temperatures (50, 100, 150, 200 and 250°C) is studied. The total elongation in uniaxial tension increases with increasing temperature in range of 50-200°C and decreases with increasing strain rate. But it drops sharply at 250°C. SEM observations of the fracture surface interpret the change of total elongation and show the fracture tends to transit from brittle mode to ductile mode with increasing temperature. The constitutive model and yield function related with temperature are established based on the experiment results.

Abstract: It is indicated that the fluid flow does not abide by the Darcy law in certain low permeability reservoirs. The results of pressure date analysis in these low permeability reservoirs would be inaccurate when generalized using Darcy flow models. To improve analysis results, based on the concept of variable permeability effect, the dual non-Darcy coupling flow model is established in this paper. The iterative algorithm is adopted to solve the differential set of equations. This work also describes the pressure behaviors by pressure response curves.