Advanced Materials Research Vols. 306-307

Abstract: Mg-RE electrode was used for deposition of micro-arc coatings on AZ31 magnesium alloy upon variation in there different processing parameters(high, low and middle pulsed discharges). Mass transfer trends from electrode to substrate and microstructure of Mg-RE coating on AZ31 substrate were observed. Characterization has been performed by using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). The microstructure, properties (continuity, thickness) were investigated. It is found that an increase in the energy mode above a certain threshold value leads to an increase in mass gain from electrode to substrate.

Abstract: In this study, surface oxygen diffusion-hardened treatment for TC4 titanium alloy was carried out to enhance the wear and corrosion resistance. The surface oxygen diffusion-hardened treatment was performed in an electrical resistance furnace under atmosphere. Characterization of modified surface layers was made by means of microscopic examinations, microhardness measurements and X-ray diffraction (XRD) analysis. The wear resistance of both treated and untreated samples was evaluated. The accelerated corrosion tests in HCl solution was used to determine the corrosion resistance. The corrosion and wear resistant surface layers were obtained after treatment. The surface layers mainly consisted of rutile TiO₂. A significant increment in surface hardness was achieved due to the formation of an oxygen diffusion zone. Corrosion and wear resistant surface on TC4 were obtained after the formation of diffusion zone.

Abstract: On the basis of measuring the electrical resistivity of Sn melt and referring to analysis of high temperature XRD, the change of electrical resistivity and structure for Sn melt with temperature was carried out. The results show that there is discontinuous change of electrical resistivity for Sn melt with the temperature in the metrical temperature range. There is a correlation between the electrical resistivity change and the structure change of Sn melt. The correlation radius and the fluid cluster size of Sn melt decrease with the increasing of temperature, so that the electrical resistivity of Sn melt increases. But there is an anomalous change in the vicinity 673K, it results in a discontinuous change in electrical resistivity of Sn melt.

Abstract: Microbial carbonate precipitation had been proposed as alternative technique for improvement in concrete materials. Laboratory experiments were conducted by bacterially mediated carbonate deposition on the surface and subsurface of concrete specimens. The crystal phase, morphology and growth of the crystal deposited on specimens as well as the efficiency of bonding and protection were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and ultrasonic test. Water absorption and the resistance of carbonation of concrete were analyzed by water absorptivity test and concrete accelerated carbonation test, respectively. Results show that phases of crystal are calcite and vaterite. The crystals are deposited uniformly on the surface of specimens. Biodeposotion effectively reduces capillary water uptake and carbonation rate constant.

Abstract: Extrusion process of a large diameter thin-walled aluminum profile was simulated by Arbitrary Lagrangian Eulerian (ALE) algorithm based on HyperXtrude software. The results show that the material flow velocity in the bearing exit of the initial design die is non-uniform. Three times modifications were performed and simulated. The optimal design with more uniform flow velocity in the bearing exit was obtained.

Abstract: High temperature electrochemical synthesis of tungsten boride has been performed in KF-KCl melts with B₂O₃ and WO₃ used as reactants at 1033K. The cathode product was investigated in the current density range 0.4A/cm²-0.6A/cm² and characterized by means of XRD analyses and SEM. The results indicated that cathode product is mainly consist of W₂B₅ and WB₄, the powders are fine (＜0.5um). Current density exert a great effect on the phase composition, particle size and morphology of the cathode product.

Abstract: In order to have good dephosphorization, it is beneficial to know the proper physical properties, including the melting point and viscosity of slag with fixed lime activity for steel refining, slag foaming and reaction in steel making. A fast way to determine the melting point and viscosity of complex multi-component slags is needed to control the quality of steel. In this study, experimental slag of FetO-CaO-SiO2-MgO-MnO-Al2O3 is obtained with electro slag remelting technique. The liquidus temperature of slag is determined with a video-based contact angle meter recorded with a high-speed camera and verified with an isopleth phase diagram of slag constructed with thermodynamic software FACTSAGE. The viscosity of liquid slag can be estimated with the optical basicity and liquidus temperature obtained from the calculated isopleth phase diagram, then it was compared with the experimental value measured by the rotating torque viscometer. The results indicated that substantial error between the calculated temperature of isopleth phase diagram and the value determined with method of contact angle in high basicity slag. On the other hand, minor difference exists between calculated liquidus temperature and measured temperature in low basicity slag. The viscosity estimated from the optical basicity and liquidus temperature of isopleth phase diagram show the similar behavior. It has good correlation between the calculated value and experimental value in low basicity, however, deviations are found in the range of high basicity.

Abstract: Microstructure and mechanical behaviors of AZ91 cast magnesium alloys with melt superheating and thermal rate treatment technique were studied. Alloy grains thicken at 820°C and refine at 870°C when they contains Mn element and the crucible had no coating on the internal surface. Moreover, the strengthening γ phase is more dispersive and uniform at 870°C. Thermal rate treatment significantly improved the microstructure, mechanical behaviors and casting quality of AZ91 alloy as microstructure of AZ91 alloy reserves some characteristics of the high temperature melt.

Abstract: Refining performance and mechanism of Al-5Ti-1B and Al-5Ti-0.4C master alloys at different temperature were investigated in this paper. The experimental results show that the refining effect of Al-5Ti-0.4C master alloy becomes worse as temperature increasing from 750°C to 1200°C, The refining effect of Al-5Ti-1B master alloy becomes worse as temperature increasing from 750°C to 1000°C. However, when the temperature is above 1000°C, the refining effect of Al-5Ti-1B master alloy recovers gradually as temperature increasing. TiB2 particles with TiAl₃ layers are the heterogeneous nucleating cores of α-Al at low temperature. However, TiB₂ particles are the heterogeneous nuclei of α-Al at high temperature.

Abstract: This work compared the densification behavior and pores evolution of two kinds of samples (15% and 35% initial porosity stainless steels parts) prepared by selective laser sintering. The results show that post microwave sintering process results in an increase of the density of sample. At the low sintering temperature (1200°C, 1300°C), the low porosity can lead to high density in the final sintered sample. As the sintering temperature reaches 1400°C, however, the sample with 35% initial porosity could be sintered to the higher final density than that of the sample with 15% initial porosity. The results also indicate that the initial porosity has a great effect on the number of pores, pore size, pore shape and the distribution of pores during post sintering process.