Effect of activating flux on arc shape and arc voltage in tungsten inert gas welding

The effects of activating fluxes on welding arc were investigated. A special set of water-cooling system and stainless steel were used as parent material. During welding process, high-speed camera system and oscillograph were used for capturing instantaneous arc shape and arc voltage respectively. The experimental results indicate that the SiO2 flux can increase the arc voltage, while TiO2 has no this effect on arc voltage. Compared with conventional tungsten inert gas welding （C-TIG）, it is found that the arc shape of A-TIG welding used with the SiO2 flux has changed obviously.     

Microstructure and mechanical properties of tungsten inert gas welded–brazed Al/Ti joints

The tungsten inert gas welding–brazing process using Al-based filler metal has been developed for joining 5052 Al alloy to Ti–6Al–4V alloy in a butt configuration. The results indicated that heat input influenced the morphology and thickness of the interfacial reaction layer of Al/Ti joints, which played an important role in the mechanical properties of weldment. With the optimised tungsten electrode offset D of 1.0?mm from Al/Ti initial interface to Al side and welding current of 70?A, the thin cellular-shaped and club-shaped TiAl₃ reaction layers formed in the brazing zone, which contributed to suppressing crack initiation and propagation during tensile test. Eventually, the maximum tensile strength of 183?MPa was obtained and the optimised Al/Ti joint fractured at Al alloy base plate. Moreover, the power density characterisation and joining mechanism of Al/Ti joints were discussed.     

Microstructure and mechanical properties of tungsten inert gas welded–brazed Mg/Ti lap joints

The tungsten inert gas (TIG) welding–brazing technology using Mg based filler was developed to join AZ31B Mg alloy to TA2 pure Ti in a lap configuration. The results indicate that robust joints can be obtained with welding current in the range of 60–70 A and welding speed of 0·2 m min^?1. The joints were found to be composed of the coarse grained fusion zone accompanied with the precipitated phase of Mg₁₇Al₁₂, and a distributed Mg–Ti solid solution zone at the interface of Mg/Ti, indicating that metallurgical bonding was achieved. The maximum tensile–shear strength of 193·5 N mm^?1, representing 82·3% joint efficiency relative to the Mg alloy base metal, was attained. The optimised Mg/Ti joint fractured at Mg fusion zone upon tensile–shear loading, mainly caused by grain coarsening. Moreover, the fracture surface practically consisted of scraggly areas, which was characterised by equiaxed dimple patterns accompanied with a few lamellar tearing.     

Influence of arc pressure on the forming of molten pool in tungsten inert gas arc butt welding with micro gap for tantalum sheet

0IntroductionHaving better plasticity and workability, high meltingpoint, and excellent resistance to a lot of sour, ethanol,chloride, sulphuret and other chemical articles, tantalumis a rare and important strategic material and nowhas beenwidely applied in some fields such as chemical, aero-space, atomic, electronic industrial, etc[1]. For continu-ous tungsten inert gas welding of tantalum sheet, becauseof high welding speed, thin thickness of workpiece andcertain butt gap, some shaping defec…     

Preparation and preliminary testing of cermet inert anode for aluminum electrolysis

1　INTRODUCTIONAluminumhasthelargest productivityamongthenonferrousmetals ,2 4Mtperyearintheworld .Whilegreatprogresshavebeenmadeintheprimaryaluminum production ,theindustrycontinuestopur sueresearchtosolvesomeformidablechallenges ,suchas quitealargeenergyintensity(14 0 0 0 15 0 0 0kW·hpertonaluminum) ,highcon sumptionofcarbonanode(5 0 0 6 0 0kgpertonalu minum) ,significantemissionsofgreenhousegas(1.71tpertonaluminum )andotherdetrimentalgases ,highcapitalinvestmentandcost[1] .Inertelectr…     

Influence of pre- and post-weld heating on weldability of modified 9Cr–1Mo(V–Nb) steel pipe under shielded metal arc and tungsten inert gas welding processes

Abstract

Welding of modified 9Cr–1Mo(V–Nb) steel pipes has been carried out via shielded metal arc (SMA) and tungsten inert gas (TIG) welding processes. The weld joints have been produced using different preheating temperatures, followed by post-weld heat treatment (PWHT) at various temperatures. The microstructures of the weld and of the heat affected zone (HAZ) of the weld joints have been studied under the optical microscope and correlated with the preheating and PWHT. The average hardness of the weld and different regions of the HAZ, and tensile properties of the weld joints have also been studied and correlated with the preheating and PWHT. The tensile properties of the SMA and TIG weld joints produced using preheating and PWHT at various temperatures are compared and correlated with their microstructures. It is noted that a comparatively high preheating temperature of the order of 573 K is beneficial, and PWHT is necessary to reduce the susceptibility to cold cracking of weld joints of the present steel. The PWHT at 1123 K enhances ductility to fracture, but decreases the tensile strength of the base material, causing fracture of both the SMA and TIG weld joints from this region close to the HAZ. The tensile properties of SMA welds are found to be superior to those of the TIG welds, especially for PWHT at temperatures up to 1023 K.     

Metal organophosphates:electronic structure tuning from inert materials to universal alkali-metal-ion battery cathodes

Organic cathodes for alkali-metal-ion batteries attract great attentions in recent years,but the ion storage sites are limited to some finite functional groups.This is because an organic cathode must have proper lowest unoccupied molecular orbitals(LUMO) to accept electrons at high potential.Herein,a novel type of organophosphate-based cathode has successfully been explored by tuning the LUMO energy level of organophosphates through metal ions with an inert electron pair.For the first time,the P...     

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.     

Superplastic forming gas pressure of titanium alloy bellows

The complex superplastic forming (SPF) technology applying gas pressure and compressive axial load is an advanced forming method for titanium alloy bellows, whose forming process consists of the three main forming phases namely bulging, clamping and calibrating phase. The influence of forming gas pressure in various phases on the forming process was analyzed and the models of forming gas pressure for bellows were derived according to the thin shell theory and the plasticity deformation theory. Using the model values, taking a two-convolution DN250 Ti-6Al-4V titanium alloy bellows as an example, a series of superplastic forming tests were performed to evaluate the influence of the variation of forming gas pressure on the forming process. According to the experimental results these models were corrected to make the forming gas pressures prediction more accurate.     

Numerical simulation of gas metal arc welding temperature field

The infrared camera is used to investigate the temperature field of gas metal arc welding.The results show that the temperature distribution of weld pool and adjacent area appears cone shape.A new heat source model combined by Gaussian distribution heat source of the arc and conical distribution heat source of the droplet is set up based on the experimental results, and with the combined boundary conditions,the temperature field of gas metal arc welding is simulated using finite element method.According to the comparison between the results of experiment and simulation in temperature field shows that the new combined heat source model is more accurate and effective than the Gauss heat source model.     

Melt metal sheet breaking mechanism of close-coupled gas atomization

The gas atomization is the process that a liquid mass is disintegrated into a collection of liquid melt droplets by the impact of high velocity gas stream and solidified into metal particles. However, the liquid melt sheet breaking mechanism has not been fully understood. So the experimental research was carried out under the condition of lower melt superheat. The results reveal that there are three approaches about melt metal sheet＇s breakage： from the edges of sheets, from inner surface of sheets, and disrupted by other droplets and sheets. The approach of melt sheet breakage is dependent on its thickness. The thicker sheets （above 25μm） are disintegrated mainly by the way of droplet＇s departing from edges, and the thinner sheets （below 10 μm） are chiefly breaking from the inner surface.     

Modeling corrosion behavior of gas tungsten arc welded titanium alloy

The pitting corrosion characteristics of pulse TIG welded Ti-6Al-4V titanium alloy in marine environment were explained. Besides the rapid advance of titanium metallurgy, this is also due to the successful solution of problems associated with the development of titanium alloy welding. The preferred welding process of titanium alloy is frequently gas tungsten arc（GTA） welding due to its comparatively easier applicability and better economy. In the case of single pass GTA welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The benefit of the process is utilized to obtain better quality titanium weldments. Four factors, five levels, central composite, rotatable design matrix are used to optimize the required number of experiments. The mathematical models have been developed by response surface method（RSM）. The results reveal that the titanium alloy can form a protective scale in marine environment and is resistant to pitting corrosion. Experimental results are provided to illustrate the proposed approach.     

Fabrication of AIN-TiC/Al composites by gas injection processing

The fabrication of AlN-TiC/Al composites by carbon- and nitrogen-containing gas injection into Al-Mg-Ti melts was studied. It was shown that AlN and TiC particles could be formed by the in situ reaction of mixture gas （N2 ＋ C2H2 ＋ NH3） with Al-Mg-Ti melts. The condition for the formation of AlN was that the treatment temperature must be higher than 1373 K, and the amounts of AlN and TiC increased with the increase of the treatment temperature and the gas injection time It was considered that AlN was formed by the direct reaction of Al with nitrogen-containing gas at the interface of the gas bubble and the melt. However, the mechanism of TiC formation is a combination mechanism of solution-precipitation and solid-liquid reaction.     

Fabrication of AlN-TiC/Al composites by gas injection processing

1. Introduction Al-based metal matrix composites (MMCs) with ceramics like SiC, Al2O3, TiC, AlN, TiN, and TiB2 as the reinforcement phase have been widely studied by some researchers. It has been reported that TiC and AlN are particularly attractive because of good wettability and high stability with molten aluminum, high hardness, and elastic modulus [1-4]. To fabricate MMCs, various techniques have been developed. Among these, the in situ technolo- gies are particularly attractive b…     

Preliminary testing of NiFe_2O_4-NiO as ceramic matrix of cermet inert anode in aluminum electrolysis

1　INTRODUCTIONTheideaofusinginertanodes(alsocallednon consumableoroxygen evolvinganodes)inaluminumproductionisasoldastheHall H啨ｒｏｕｌｔｐｒｏｃｅｓｓ ,dat ingbacktothediscoveryofoneoftheinventors ,Hall[1] .Inertanodesareintendedtoreplacethecon sumablecarbonanodethatiscurrentlyused .Withacarbonanode ,thecellreactionisAl2 O3+ 3/ 2C =2Al+ 3/ 2CO2 (1)where　acryolite basedmelt(Na3AlF6 AlF3 CaF2 )atnear 96 0℃servesassolventforthealumina .Withaninertanode ,thecellreactionwillbeAl2 …     

Results from 100 h electrolysis testing of NiFe2O4 based cermet as inert anode in aluminum reduction

1 Introduction Since the Hall-Héroult process was applied in aluminum production, an inert anode was always the target that the aluminum industry was seeking for in the new technology field[1]. Some selection criteria have been defined in order to ident…     

Study on chaos in short circuit gas metal arc welding process

Based on the chaos theory, an idea is put forward to analyze the short circuit Gas Metal Arc Welding （ GMAW-S） process. The theory of phase space reconstruction and related algorithms such as mutual information and so on, are applied to analyze the chaos of the GMAW-S process. The largest Lyapunov exponents of some current time series are calculated, and the results indicate that chaos exists in the GMAW-S process. The research of the chaos in the GMAW-S process can be help to get new knowledge of the process.     

Preliminary testing of NiFe2O4-NiO-Ni cermet as inert anode in Na3AlF6-AlF3 melts

1 Introduction It is well known that the current aluminum reduction cell with carbon consumable anode has many disadvantages. So the concept of inert anode was introduced, with which the disadvantages can be avoided completely. A lot of research work has…     

Modeling of gas phase diffusion transport during chemical vapor infiltration process

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