Papers by Author: Zhen Luo

Abstract: In order to investigate the effect of active fluxes on weld penetration, angular distortion and weld morphology in gas tungsten arc welding (GTAW), three types of oxide fluxes-CaO, TiO₂ and Al₂O₃-were used in the welding of 5mm think stainless steel plates. Those powders were applied through a thin layer of the flux to produce a bead on plate welds. The results showed that compared with conventional TIG welding, increased weld penetration and reduced angular distortion of the weld piece were obtained with the application of active fluxes. However, the weld morphology was not changed significantly when the powders were coated on the surface of steel. It was also found that each of the powders has a fittest range in penetration increment. Whether the rate of the coating run out of the range, the effects of these active fluxes on the increased weld penetration were not obvious. The CaO flux has a narrow effective range for deep penetration, while the Al₂O₃ powder does have no effect on A-TIG penetration. The mechanism of those different performances has not been found out. According to the investment, the mechanism of active fluxes for the increased weld penetration and reduced angular distortion is related to the contraction of the arc.

Abstract: The corrosion behaviors of 304 stainless steel (304SS) which has been cut and 304SS which has not been cut in two different solutions were investigated using polarization curve and electrochemical impedance spectroscopy (EIS) methods. The results show that 304SS which has been cut and 304SS which has not been cut have the similar corrosion voltage in two different solutions. However, the corrosion velocity of 304SS which has been cut is more than 304SS which has not been cut both in the two solutions and the corrosion behaviors of two 304SS in the water solution are better than in the water which has little oil.

Abstract: In this paper, to obtain hardfacing alloys with Anti-wearing，nine kinds of low-hydrogen type coating are designed with orthogonal optimization method and carbon, chromium, erbium and cerium are taken as four factors. The mechanical properties of each hardfacing layer are tested and the microstructure is analyzed. The optimal dosage of the four elements is found by R/S analysis method. There is no crack in continuous surfacing with the electrode prepared with optimal formula, the wear resistance of the corresponding hardfacing layer is good while the hardness reach to 57.9HRC, the microstructure is martensite, a small amount residual austenite and dispersed carbide.

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: 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: 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: Resistance spot welding (RSW) is an important welding process in modern industrial production, and the quality of welding nugget determines the strength of products to a large extent. Limited by the level of RSW quality monitor, however, RSW has rarely been applied to the fields with high welding quality requirements. Associated with the inversion theory, in this paper, an electromagnetic inverse model of RSW was established, and the analysis of influence factors, such as the layout of the probes, the discrete program and the regularization method, was implemented as well. The result shows that the layout of the probe and the regularization method has great influence on the model. When the probe is located at the y direction of x-axis or the x direction of y-axis and Conjugate Gradient method is selected, a much better outcome can be achieved.

Abstract: A three-dimensional model is developed to study the dynamic process of three-roll plate bending using finite element method (FEM). In this work, the continuous three-roll bending configuration with cylindrical rolls is used to bend a thick plate into a cylindrical shape. It presents the geometrical setup and the finite element model. This 3D simulation is based on the elastic plastic explicit dynamic FEM under the ANSYS/LS-DYNA environment. Effect of initial strain and change of material properties during deformation is neglected. In order to investigate the influence of parameters on the process, top roller position, friction between rolls and plate, and temperature are also discussed. It is found that the simulation program is a feasible and economical method to study the influence of these parameters, and the FEM simulation can also provide engineers with a convenient analytical tool for optimizing process parameters.

Abstract: The strength and microstructure characteristics of the nugget in aluminum ally resistance spot welding were evaluated in this study with and without addition of rare earth elements Er, Ce. The strength was assessed using a small punch test mode and the microstructure was studied using an optical microscope, scanning electron microscope, and energy-dispersive spectroscope. Results indicated that the hardness and strength were increased about 10% after adding rare earth elements Er, Ce in the nugget. The grain of nugget zone was refined significantly. In the boundary and interior of the grain, a number of rare elements and its compounds were dispersed. This showed that parts of rare earth elements existed as solid solution in Al Matrix, part as the rare earth compounds. This improved that the elements not only can promote nucleation and refinement, but also can inhibit plastic deformation by hindering the dislocation movement. Thus they could play a strengthened role. The strengthening mechanism of the rare earth elements Er, Ce in the alloy nugget is mainly the second phase strengthening and fine grain strengthening.

Abstract: A simple and reliable welding method was developed to weld carbon nanotubes with the power supply here. The carbon nanotubes were synthesized chemical vapor deposition method and Multi-walled carbon nanotubes was uesd here. Firstly, apply less than 5 V voltages between carbon nanotubes when they were in close proximity under direct view of optical microscope. Then, let carbon nanotube contact with each other and increase the external voltage to 7–8V until carbon nanotube was attached to the end of the other, the two carbon nanotube join into a carbon nanotube. Furthermore, some experiments were implemented to analyze the reliability, the images of the weld joint and the weld strength all indicted this method were reliable.