Gas tungsten arc welding of titanium using flux cored wire with magnesium fluoride

Abstract

Grade 2 Ti–CP was gas tungsten arc welded using flux cored (FC) wires and flux pastes that contained various MgF₂ contents. The effects of MgF₂ on bead morphology, chemical composition and hardness of weld bead were investigated and interpreted. With an increase of MgF₂ content in the flux paste, depth/width ratio of weld bead increased gradually with little variation in interstitial element contents and hardness. Weld bead made with cold FC wire feed showed even deeper and narrower bead, indicating the greater effectiveness of wire feed than flux paste on weld penetration. While the 50% MgF₂ FC wire produced complete slag coverage and smooth weld bead surface, 85% MgF₂ wire resulted in incomplete slag coverage and rough weld surface. Arc spectroscopy revealed that the 50% MgF₂ FC wire produced plasma spectrum with atomic and ionised titanium peaks, which is an indication of a high temperature arc and a larger amount of flux vapours in the arc. Therefore, it is believed that deep weld penetration associated with high MgF₂ fluxes in this experiment is caused by arc constriction, resulting from the greater amount of flux vapours owing to high arc temperature.     

电磁继电器磁干扰试验的恒定磁场发生器

针对以往生产厂家一直未给出继电器产品的电磁兼容性指标问题,设计并实现了一种可用于电磁继电器磁干扰试验的磁感应强度连续可调的干扰磁场发生器.采用FLUX软件计算了恒定磁场与励磁电流之间的关系,给出了磁感应强度的分布图景及均匀度.针对MY2NJ型拍合式电磁继电器,试验得出干扰磁场对其吸合电压、释放电压等特性参数的影响.     

基于FLUX(R)的永磁无刷电机齿槽转矩抑制的仿真研究

基于Cedrat公司FLUX(R)软件的仿真环境,建立了永磁无刷电机的仿真模型,对比研究了辅助凹槽深度、宽度及数目对电机齿槽转矩的影响,为永磁无刷电机齿槽转矩抑制提供了一定依据.     

Welding of titanium alloys with activating flux

Abstract

In the present paper, the effects of an activating flux on Ti–6Al–4V alloy welding were investigated. Tungsten inert gas welding was used to weld 8.0 mm thickness Ti–6Al–4V alloy plates. Results show that applying the activating flux on the Ti–6Al–4V alloy surface leads to an increase in weld penetration depth, whereas the corresponding weld bead width is reduced. It was also found that various welding conditions, particularly flux thickness, influence the effectiveness of the activating flux. Furthermore, a data acquisition system was used to monitor the current and voltage signals during welding. Results from monitoring of the welding current and voltage signals reveal that there is a clear correlation between the signals and the weld penetration when the welding arc is steady. Analysis of the acquired signals can be used to identify inconsistencies in weld penetration. In summary, to take advantage of the use of activating flux in Ti alloy welding, it is important that a uniform flux layer is present at the alloy plate surface and suitable welding parameters are selected.     

Welding of magnesium alloys with activating flux

Abstract

The effects of an activating flux on AZ31B alloy welding were investigated. Alternating current tungsten inert gas (ACTIG) welding was used to weld 5·0 mm thick AZ31B alloy plates with CdCl₂, AlF₃ and TiO₂ activating flux. Applying the activating flux on the AZ31B alloy surface led to an increase in weld penetration depth. Various welding conditions, such as welding current, welding arc length, welding shielding gas flowrate, welding speed and flux thickness, influenced to different extents the ability of the activating flux to increase weld penetration. Furthermore, a high speed camera was used to monitor the arc images during welding. It was found that the brightest region of the arc was broader when CdCl₂ and AlF₃ were used, while the stability of the arc was increased when TiO₂ was used, especially in the positive electrode period. In summary, it is important that a uniform flux layer is present at the alloy plate surface and suitable welding parameters are selected.     

Effect of aluminium on microstructure and mechanical properties of self-shielded flux cored welds in low carbon steel plate

Abstract

In the present paper, the results are reported of an investigation dealing with the inclusions, microstructure and mechanical properties of self-shielded flux cored welds with different aluminium contents. Results show that the total number and number density of inclusions in the low aluminium weld are higher than those of the high aluminium weld. However, the average size and the contamination rate of inclusions in the low aluminium weld are 0·77016 μm and 0·022%, which are lower than those of the high aluminium weld. The weld with a low aluminium content contains finer inclusions and the weld with a high aluminium content contains mainly coarser inclusions. There are remarkable differences in microstructure between the welds with different aluminium contents. The reheated zones in the weld made using flux no. 1 are larger than those in the weld made using flux no. 2, which are occupied by skeletal δ ferrite columnar crystals. As a result, a drastic reduction in impact toughness is observed in the high aluminium weld. Fracture examination shows that the low aluminium fracture surface consists mainly of small ductile dimples and a quasi-cleavage fracture area. The fracture surface of the high aluminium weld comprises mainly larger dimples and a cleavage fracture area. Inclusions in the low aluminium weld are mainly small Al₂O₃–MgO spinel with an approximate round shape, and some AlN inclusions. In the case of the high aluminium weld, inclusions are almost all large AlN. Finally, the results of thermodynamic analysis agree with the trends observed in the experimental data.     

Experimental investigation into radiative heat transfer characteristics for mould fluxes containing transition oxides

Abstract

Infrared transmittance of glassy and crystalline mould fluxes was measured using a Fourier transform infrared spectrometer at room temperature. Radiation heat transfer from the steel shell to the mould was calculated by a model. The results indicate that transition metal oxides MnO, FeO and TiO₂ have a marked negative effect on infrared transmittance and radiation heat flux of glassy samples. With MnO, FeO and TiO₂ added, the reductions of radiation heat flux in glassy samples are 19–25%, 34–36%, 6–29% respectively. X-ray diffraction results indicated that the crystalline phase in transition oxides free samples was mainly Ca₄Si₂O₇F₂. After transition oxides MnO, FeO and TiO₂ added, Mn₂SiO₄, Fe₂SiO₄, CaTiO₃, Ca₂SiO₄ and other minor phases were also precipitated in mould fluxes. On account of strong refraction and scattering, the negative effect on radiation heat flux in crystalline samples was much larger than that in the glassy ones.     

Weld shape comparison with iron oxide flux and Ar–O2 shielding gas in gas tungsten arc welding

Abstract

The influence of iron oxide flux and O₂–Ar mixed shielding gas on weld shape and penetration in gas tungsten arc welding is investigated by bead-on-plate welding on SUS 304 stainless with low oxygen and low sulphur contents. The oxygen content in the weld metal is measured using a HORIBA EMGA-520 oxygen/nitrogen analyzer. The results show that both the iron oxide flux and the O₂–Ar mixed shielding gas can significantly modify the weld shape from shallow wide to deep narrow. A large weld depth/width ratio around of 0.5 is obtained when the oxygen content in the shielding gas is in the range of 3000–6000 vol. ppm. Oxygen over a certain critical value, i.e. 70 wt. ppm, in the weld pool alters the temperature coefficient of the surface tension on the pool surface, and hence changes the Marangoni convection. A thick oxide layer on the weld pool surface is generated when the oxygen content in the shielding gas is over 6000 vol. ppm, which becomes a barrier for the oxygen conveyance to the liquid pool and prevents the liquid pool from freely moving, and therefore, decreases the intensity of the Marangoni convection on the pool surface.     

Adhesion of underfill and components in flip chip encapsulation

The underfill material is a polymeric adhesive used in flip chip packaging. It encapsulates the solder joints by filling the gap between a silicon die and an organic substrate or board. Within a typical flip chip structure, there are interfaces between the various components, namely, substrate, solder mask, flux residue, underfill encapsulant and die passivation layer, etc. Maintaining a good adhesion condition, both as-made and after temperature/humidity aging, is vital for these interfaces because of the expected performance of the flip chip device, where the underfill material is employed to enhance the reliability of the flip chip interconnect. We have studied the adhesion strength between the various components for different process variables as measured with the lap shear and die shear test configurations. The effects of the assembly factors, i.e. solder mask, flux residue, underfill, and die passivation, etc., were evaluated and the adhesion strength was found to depend greatly on these factors. The die shear strength of a passivated die assembled onto an organic board coated with a solder mask was much higher after using a no-clean flux on the solder mask than for the assembly without such a no-clean flux. The influence of some accelerated aging tests on the adhesion durability was also investigated. A die passivation layer of benzocyclobutene exhibited better capability in retaining the die shear strength than a passivation layer of silicon nitride or polyimide, especially for the initial aging period. The knowledge obtained in this study should provide insights into the interfacial adhesion in the flip chip assembly structure.     

共轨轨压对喷油器电磁阀响应的影响分析

影响电磁阀响应特性的参数很多,本文采用电磁软件FLUX和一维软件AMESim共同联合仿真的方法,研究不同共轨轨压下作用在衔铁杆球阀上的油压对电磁阀响应的影响,计算结果表明,随着轨压的增加,电磁力上升速度加快,电磁阀开启响应加快.