Materials Science Forum Vol. 762

Abstract: The finite element analysis on temperature field and stress field during submerged-arc welding (SAW) was carried out by means of assembly language of FORTRAN on the base of ABAQUS. A finite element model was established to study the effects on weld bead formation by using longitudinal magnetic field of low-frequency and different process parameters loaded with moving heat source. A practical SAW experiment was conducted to verify the results of the numerical simulation. It was shown that a molten pool with a wider weld face and a lower penetration could be obtained by the control of longitudinal magnetic field of low-frequency. In addition, the fusion line after this treatment was smoother than with conventional SAW. The results of practical SAW experiment were consistent with those of the numerical simulation. It was confirmed that the longitudinal magnetic field of low-frequency could contribute in diminishing the dilution rate and improving the performance of surfacing layers.

Abstract: A reproduction of the conditions occurring during friction stir processing, where a fine grained structure according to the process parameters rpm, transverse speed and pressure develops is the main focus in the present work. To physically simulate such a friction stir process, hot torsion tests at constant temperatures were carried out in a Gleeble ® 3800 machine at different strains and strain rates. The specimens were immediately water quenched after hot deformation to avoid any static recrystallization. The microstructure was investigated to characterize the grain size evolution and misorientation as a function of the local strain, strain rate and temperature. Dynamic recovery was observed followed by continuous dynamic recrystallization at large deformations. By means of DEFORM^TM3D the occurring strain, strain rate and temperature distributions, which are decisive for the observed microstructure evolution, were evaluated.

Abstract: The trend in automotive, aircraft, and marine industries is the increasing use of sheet materials to reduce weight in components and optimize materials performance. Welding is the main fabrication and assembly process in many of these industrial applications. However, in using thin-shell structures in such applications, welding may results in significant residual stresses and out-of-plane distortion. Transient thermal stresses, residual stresses, and distortion sometimes cause cracking and mismatching of joints. High tensile residual stresses are undesirable since they can contribute to fatigue failure. The analysis and measurement of temperature and stresses in component are often too complex to conduct in practise, and thus finite element models provide feasible approach to examine these matters. In this paper, finite element analysis has been performed using the ANSYS package to study the behaviour of longitudinal residual stress and strain in a welded thin aluminium-manganese alloy. The model presented simulates conventional welding and welding with the introduction of welding mitigation technique for enhancement of heat transfer, in which a trailing heat sink was applied. The thermal profiles obtained using the mitigation technique is completely different from those obtained in the conventional cooling. The localized transient residual stress and through-thickness strain after applying a cooling sink are discussed. The transient residual stress behaviour was highly affected by the modified temperature distribution and magnitude due to introducing the heat transfer enhancement.

Abstract: In the present study, Cu-Sn-Ti filler alloy with different content of Sn was used to join Ti₂AlC ceramic and copper at 950 °C for 10 minutes. Effect of Sn content on the microstructure, mechanical property and electrical conductivity of the joints were investigated.The results indicate that the joint was comprised of five parts: copper substrate/ diffusion area in the copper substrate (Cu [Al, S solid solutions)/ brazing layer (Cu [Al, S+CuSn₃Ti₅)/ interaction area in the Ti₂AlC substrate (Ti₂AlC+ Cu [A+AlCu₂Ti+TiC)/ Ti₂AlC ceramic substrate.With the content of Sn element in the joint increasing, the filler alloy performed lower melting point and better fluidity during brazing. Thus partial filler alloy flowed out of the brazing seam, leading to the reduction of CuSn₃Ti₅ phases. Simultaneously, more Ti and Al diffused toward the Cu substrate, where a line of AlCu₂Ti phases was formed. The maximum shear strength 158.5 MPa was obtained by using Cu80Sn10Ti10 (at.%) filler alloy, at which the joint strength was 71% of that of the Ti₂AlC ceramic. The joint strength was deteriorated while the higher content of Sn was incorporated (>10 at.%), which was caused by the weak interfacial bonding between the substrates and the brazing layer. Besides, the electrical conductivity was decreased from 5.65×10⁶ s/m to 4.99×10⁶ s/m with increasing Sn content in the filler alloy.

Abstract: The reaction process between Ti₂AlC and Ag-Cu filler alloy was mentioned in our previous study. However, the reaction mechanism between Ti₂AlC and filler alloy remained uncertain due to the existence of TiAl₂, which was widely distributed in the dual-phase Ti₂AlC substrate and exhibited intense reaction with Cu. In current research, pure-phase Ti₂AlC was brazed to Cu using Ag-Cu filler alloy respectively at 850°C and 900°C for 10 min. First of all, to investigate the influence of TiAl₂ on clarifying the reaction mechanism, Ti₂AlC substrates with different component (single phase and dual phase) were joined to Cu at 850°C for comparison. However, in these joints, it was difficult to find any other reactant except for AlCu₂Ti. Thus, the pure-phase Ti₂AlC was brazed to Cu at 900°C, aiming to intensify the interaction between substrates and filler alloy. For characterizing the microstructure evolution in the joint, the typical region of the joint that contained all the reactants was selected and sliced by focused ion beam technology. Combining with transmission electron microscopy, all the decomposition products (e.g. Ti₃AlC₂ and TiC) in the joint were identified. Then the decomposition mechanism of Ti₂AlC was clearly disclosed.

Abstract: Reducing the cost of composite material production is significant for expanding its usage and application in many ways, such as in the fields of aerospace, aviation, ocean industry and so on. To do this, It is important to minimize the production process of the material and to decrease the amount of scraps or any unnecessary particles. The Vacuum Assisted Resin Transfer Molding (VARTM) process, which is known for having many advantages, has become recognized as one of the most low-cost manufacturing model. VARTM process can be divided into three main steps: performing, resin filling and hardening steps. The most important step among all these three steps is the Resin Filling stage, a process when resin is impregnated into the mat. Mostly, Resin Filling stage is greatly affected by the level of permeability, a characteristic of stiffener due to pneumatic resistant nature in the process. Other factors such as viscosity, technological vacuuming, or even stiffening process itself could also influence the production as well. During Resin Filling stage, Resin tends to spread out in the center first because of capillary phenomenon. In this research, the researchers examined the mechanical property and the pneumatic nature of Resin by dividing the pneumatic movement of the Resin into sections. Based on this result, the researchers found the correlations between the capillary phenomenon and Resin impregnation, and analyzed the movement mechanism in Resin filling stage.

Abstract: nfluence of friction and lubrication on formability of an aluminium alloy (AA5182) in hydroforming of square cups has been studied experimentally and numerically. Three friction conditions were created at the blank-die interface using hydraulic oil, Teflon and dry condition (no lubrication). Maximum thinning and minimum radius at the cup corners were taken as criteria for formability evaluation. Formability improved to a great extent with Teflon sheet as the lubricant. Lower friction allowed better draw-in of the material with higher uniformity of strain distribution and the maximum pressure that the material can sustain has significantly increased.

Abstract: Simulation of multiple-step incremental roll-bending forming and springback of large-scale sheet metal with U shape was implemented in this paper using ABAQUS. In view of the semi-ellipse shape of work piece, a geometric plan using fives arcs with different radius to approach the original shape in piecewise is proposed. On the basis of the programming, reasonable arrange the rolling steps, adjust the parameters in ABAQUS. The largest error of curvature radius of different arcs is less than 5% after simulation of the sheet metal forming according to optimized process fitting with Origin8.0. The results show that the incremental roll-bending method forming the semi-ellipse shape work piece is feasible.

Abstract: The effect of major parameters, such as pouring temperature, tilt time and preheating temperature of mold, on the tilt casting of aluminum alloy automobile drain pipes is studied through numerical simulation using single factor and orthogonal test methods. The simulation results of single factor test indicate that the increase in the pouring temperature and mold preheating temperature could effectively reduce the shrinkage tendency and the shortage of tilt time would cause lower temperature gradient of casting at the beginning of solidification, thus would lead the extension of solidification time. And the results of orthogonal test showed that the sequence of factors having effect on the filling and solidification process, are pouring temperature, tilt time and preheating temperature of mold. Finally, combined the result of single factor test with orthogonal test, an optimized tilt-casting process was proposed by investigating the velocity distribution at each stage of the filling process and the isolated area distribution of liquid phase in the solidification process, and by predicting the position of porosity in the casting. The effectiveness of the proposed process parameters in producing high quality castings is also proved through numerical simulation.

Abstract: In this paper, organic aluminum compound, aluminum tris (tetradecylacetoacetate) (Al-14) was synthesized, and its molecular structure was identified by IR spectrum. The investigation of the curing kinetic of epoxy resin system with PhS (4, 4-dihydroxydiphenylsulfone)/aluminum tris (tetradecylacetoacetate) (Al-14) latent catalysts was performed by differential scanning calorimetry (DSC) using an isothermal approach. All kinetic parameters of the curing reaction including the reaction order and activation energy were calculated and reported. The results indicated that the curing reaction of Ep/PhS/Al-14 compand system in this experiment proceeded through an autocatalytic kinetic mechanism.