Advanced Materials Research Vols. 146-147

Abstract: The microstructure and mechanical properties of aged Mg-5.5Al-0.5Y magnesium alloy with Sm addition were investigated. The results show that with proper content of Sm addition, the microstructure of Mg-5.5Al-0.5Y magnesium alloy is refined obviously. The quantity of β-Mg17Al12 phase is reduced, and Al2Sm particle phase is formed. With the increase of Sm addition, the mechanical properties of the alloy at room and elevated temperature increase at first, and then decrease. When the content of Sm is up to 1%, the values of tensile strength and elongation at room temperature,150 and 175 are up to their maxima synchronously, 244MPa/20.07%, 217MPa/18.86% and 185MPa/19.15% respectively.

Abstract: A coupled numerical simulation of magnetic field and flow field was conducted basing on Φ250mm bloom during continuous casting with electromagnetic stirring.The distribution of the flow field was analyzed in different current and frequency.At the same current,the velocity first decrease and then increase as the frequency increase along the casting direction.At the same frequency, tangential velocity is dominant in the radial of EMS center,velocity increase with the current. Considered the results of numerical simulation,the optimized EMS parameters of Φ250mm bloom are the stirring current of 480A and the stirring frequency of 3Hz.

Abstract: This paper reported results of an investigation aiming at finding what affected the orientated grain growth of Bismuth titanate niobate (Bi3TiNbO9) by spark plasma sintering process (SPS). Single phase of textured Bi3TiNbO9 (BTNO) ceramics were prepared by a two-step sintering method: synthesizing seed-crystal platelets by molten-salt method with oxide mixture as precursors and then sintering the platelets under different SPS conditions such as heating rate, holding time, sintering temperature and pressure, etc. The possible effects of these factors upon the textured microstructure have been analyzed in detail. Textured Bi3TiNbO9 ceramics with different orientation degree was obtained by controlling the conditions during SPS process.

Abstract: Electroplating was employed to prepare Cu films on Fe substrates and Ni substrates. The average internal stresses in Cu films were measured in situ by cantilever beam test. The distribution of the internal stresses in Cu films was investigated. The results show that the average internal stresses and the distributed internal stresses in Cu films decrease abruptly with the increase of film thickness when the films are thinner. The interfacial stresses in Cu films are very large and growth stresses are very small. The average internal stresses in Cu films, which were caused by the adjustment of the electron densities at either side of the interface, were calculated roughly using a modified Thomas–Feimi–Dirac electron theory. For the same substrate and the same film, the theoretical value of the average internal stress in film is about equal to the experimental value. It shows that the theoretical calculation model of internal stress is of accuracy.

Abstract: To improve the current efficient of Al-Zn-Sn alloy, the influence of different contents Ce on the microstructures and electrochemical properties of alloy was investigated. The results show that the appropriate amount of Ce was effective on improving the electrochemical properties of Al-Zn-Sn alloy. The corrosion potential shifted negatively and the current efficiency increased with the increasing of Ce contents. The optimal microstructure and electrochemical properties were obtained when the Ce content in the alloy was 0.5 wt.%. The good electrochemical properties of Al-7Zn-0.1Sn- 0.5Ce (wt.%) alloy is mainly attributed to the fine grains and the less segregation phases at grain boundary.

Abstract: A direct current was imposed during the ageing treatment of cold worked Cu-Cr-Zr alloys. The effect of increasing current density and ageing time on the electrical conductivity and microhardness has been investigated. The electrical conductivity was found to increase by about 22% IACS to a maximum value of 90% IACS. Furthermore, the microhardness increased by 21 HV up to 176 HV. A number of Cr precipitates and Cr-rich clusters were observed after the ageing treatment with direct current. The direct current was found to significantly enhance the efficiency of precipitation which is most probably due to the electron wind force and the electromigration-induced mass transport.

Abstract: The effect of high density of pulsed electric current on directional solidification of pure aluminum was investigated. The solidified microstructure experiences three evolution stages with increasing of current density, which are regular columnar structure to cellular crystal, cellular crystal to dendrite, and dendrite to columnar crystal. The influence of pulsed electric current on microstructure was analyzed by means of coupling effect between induced electromagnetic field and electric current.

Abstract: In order to discuss the abnormal fracture in drop weight tear test (DWTT) of API X80 medium-thickness plate, some unqualified samples in DWTT are characterized by SEM, AES, electrolysis and thermal simulation. SEM results show that there are many spherical precipitates in the fracture surface. EDS and AES results show that the abnormal spherical precipitates are carbides including Fe, Ni, Mo, Ti, etc. These precipitates can be extracted by neutral electrolyte method and their EDS results further demonstrate they are carbides. The formationmechanismof the precipitates is discussed based on thermal simulation experiments. When the cooling rate of medium-thickness plate is not enough high, especially in carbide formation area in Fe-C diagram, abnormal spherical carbides will occur and they are harmful for DWTT.

Abstract: A comparative study of the morphology and anticorrosive behaviour of commercial 55 wt% Al-Zn-Si coatings (CC) and hot-dip 55 wt% Al-Zn-Si coatings (HD) on Q235 steel was performed by using surface analysis techniques and electrochemical measurements. Despite the ingredients of the Al-rich dendritic phase for HD coating similar to the ingredients for CC coating, aluminum content in the Zn-rich phase for HD coating was almost twice higher than aluminum content for CC coating. The difference of surface morphologies and chemical compositions in Zn-rich phases for the two 55 wt% Al-Zn-Si coatings could significantly affect their corrosion properties. The corrosion behavior of the two coatings was investigated in 0.01 mol L-1 NaCl + 0.01 mol L-1 NaHSO3 aqueous solution. Both polarization curve and electrochemical impedance spectroscopy results indicate HD coatings had much higher corrosion resistance than CC ones.

Abstract: The synergistic toughening of UPR composite by rigid particles of organic PA6 and inorganic nano-SiO2 was studied. The effects of PA6 and SiO2 on the notched impact and tensile strength of the UPR composite were studied by means of the mechanical properties test. The experimental results indicated that the notched impact strength was improved and its effect was evident when 7-9％rigid particles were applied and the tensile strength was improved when the 2-5％ rigid particles were applied. The composite of PA6/SiO2 ( 2/1) exhibited good mechanical property in the synergistic toughening. By the micromechanical analysis of composite, we thought that the stiffness of composite materials was determined by the stress suffered the rigid particles and the deformation of UPR polymer phase.