Advanced Materials Research Vols. 189-193

Abstract: By the way of adding rare earth element into the coating of electrode, this article has studied the effects of rare earth element erbium and cerium on the properties of welding surface. Experiment results show that adding rare earth element to the welding rod coating could make the grains fine, increase the content of acicular ferrite and improve the hardness and abrasion resistances of weld metal. After joining 0.3% Er and 0.3% Ce, the weld metal's macroscopic hardness achieves 39HRC, enhanced 23.8%. And the relative wear resistance enhanced 25.6%

Abstract: The stress-strain relationship of soil is described by fractional derivative viscoelastic model, and established the vertical governing equations of viscoelastic soil. The stiffness and damping of the soil layer described by fractional viscoelastic model are obtained based on the method of layer. The pile-soil dynamic interaction is modeled by Winkler dynamic elastic-damping model, the pile to pile dynamic interaction and vertical vibration of the pile groups in the soil described by fractional derivative viscoelastic model is solved. The influence of the pile spacing, order of fractional derivative and model parameter of soil on the vertical dynamic impedance of pile groups is also investigated. The result indicated that the curves of the dynamic impedance varying with frequency were more complex with the increase of pile spacing, the influence of the order of fractional derivative on vertical dynamic impedance of pile groups is different at lower frequency and high frequency, and the selection of the constitutive model of viscoelastic soil had great effect on the vertical dynamic impedance of pile groups.

Abstract: In this study, some Ni, Bi elements were added into low-Ag (less than 1%) Sn-Ag-Cu (SAC) solder. The effect of these additive elements on the solderability, intermetallic compounds (IMCs), and electromigration performance of low-Ag SAC (LASAC) solder were investigated. With the increase of Bi content in LASAC-0.05Ni-xBi (x=0, 2.0, 2.5, 3.0, 3.5, 4.0) solders, the peak melting point decreases while the wetting area of solder alloy increases. With the addition of Ni, the IMC between Cu pad and LASAC solder transforms from Cu6Sn5 to (Cu1-xNix)6Sn5 and the morphology of the IMC turns from bulk-like to needle-like. Either the addition of Bi or Ni will slow down the IMCs growth rate during high temperature storage aging (HTS) at 180°C and has a positive effect on electromigration performance of LASAC soldering.

Abstract: A simple ultrasonic welding method was employed to bond the carbon nanotubes and metal electrodes, at the same time, macro-body carbon nanotubes was tried in the experimental. By the welding head exert suitable pressure on carbon nanotubes bridge on electrodes with frequency of 60 kHz and power of 1.8w, contact would be achieved between these, moreover, the image of SEM show that the bonding was tightly.

Abstract: In this investigation, in order to research the influence of magnetic field on microstructure and properties of magnesium alloy welded joint, the AZ31 magnesium alloy plates which was 5mm were welded by GTAW under longitudinal magnetic field. The tensile test, hardness test and SEM were taken place to analyze the properties and microstructure of welded joint under different magentic field parameters. The acting mechanism of magentic field on welded joint was studied. The results show that: External magnetic field can improve the properties of magnesium alloy welded joint which is welded by GTAW. The optimal mechanical property will be obtained when Im=2, f=20Hz, which the ultimate tensile strength is 231Mpa and the micro-hardness is 76.2HV.The magnetic field can produce electromagnetic stirring, which can refine crystal grain through breaking the pine-tree crystals with proper magnetic field current and frequency. The properties of welded joint will been improved by these fine crystal grain.

Abstract: The effect of grit particle size on frictional characteristics was investigated using a vertically oriented brake test rig. Silica sand of grit sizes 50-180 µm, 180-355 µm and 355-500 µm were used in drag mode application. Results showed that the presence of hard particles from environment can influence the friction response significantly. Basically, once the hard particles enter the gap, the value and amplitude of friction coefficient tend to decrease. However, slight increase in friction with smaller particles was recorded due to more hard particles involved in mixing and changing the effective contact area. Better friction stability was related to the presence of smaller grit particles and compacted wear debris to form frictional film on the braking interface.

Abstract: In this paper, the distribution of residual stress is measured which is 60mm away from the weld center with the three-dimensional magnetic measurement apparatus of HZ-21. The stress distribution of plate - plate butt welding and its influence on welding deformation are studied. The results show that, plate - plate butt of Q235B steels, the welding stress distribution of σx direction is in the direction of a curve along the seam; 24 hours after welding, the welding angular deformation increases due to the changes of welding stress, while welding angular deformation also changes the stress distribution.

Abstract: The semi-solid brazing process of SiCp/A356 composites and aluminum alloy was investigated. The two substrates were heated up to the semisolid temperature range of Zn-Al filler metal in the joint region by a resistance heating plate. At this point a stirrer was introduced into the weld seam in order to mix filler metal and the two sides of substrates into a single uniform joint. After stirring, specimens were sectioned for analysis of macro- and micro-structures along the weld region. The research shows that SiCp/A356 composites and aluminum can be successfully joining with semi-solid filler metal. It can be found that most of the oxide film on the surface of the base metal was disrupted and removed through the observation by SEM. The metallurgical bonds formed between the filler metal and the base materials. Moreover, the oxide film of surface of aluminum alloy was more thoroughly disrupted and removed than that of surface of composites with existing of Sic particle. The joint microstructure with globular α-Al grain enclosed by rich-Zn phase can be obtained after stirring brazing.

Abstract: With considering the geometry characteristic of laser brazing and analyzing the action features of heat source in laser brazing, an adaptive heat source mode is constructed to simulate the dynamic response of temperature field and flow field of beryllium irradiated by a moving laser. And the shape of fusion zone and thermal cycle curve calculated agree well with the experimental results, it indicate that the proposed model is appropriate and adaptive in simulating the dynamic response of melting pool. Further, influences of latent heat of fusion and butt gap on temperature field and melting pool shape is analyzed by means of the method of numerical Analysis. The results show that the effects of the latent heat are not negligible. In particular, the influence of the latent heat is more violent under moving laser beam action than under stationary laser beam. And the predicted profile of melting pool which taking butt gap into account is more close to that of experimental results.

Abstract: The hardening behavior of the welding heat affected zone (HAZ) with different heat input for 500MPa grade screw thread steel is investigated in this paper. The single welding thermal cycle was applied to the test steel by a Gleeble-3500 thermal simulator. With the definition of hardness ratio, relative hardness factor and partial hardness zone, the HAZ Max hardness, hardness distribution and hardness mechanism of steel were analyzed. The results show that the HAZ hardness is always higher than the base steel hardness. The hardness ratio is increasing with the heat input decreased. The distribution of relative hardness factor of HAZ can be expressed by the Avrami equation which can describe the distribution of HAZ hardness. The width of partial hardness zone increases rapidly with the heat input increased. But at a certain degree of heat input, the width of partial hardness decreases slightly. The microstructure generated by heat input is the intrinsic factor of the HAZ hardness variation. The HAZ hardness enhances as the martensite content increases. On the contrary the HAZ hardness reduces as the ferrite content enhance on condition the heat input increase or the observed area is far away from the HAZ.