Under the spirit of sustainable development，‘lightweight’has been gradually included into the vehicle design criterion by many manufacturers and used in automobile production．Following this trend，domestic wheel suppliers also begin to study the technology of lightweight wheel．One way to achieve this goal is improving strength grade of the steel and optimizing the structure design in the field of steel wheels．But there are a few problems in flash butt welding process in the application of high strength steel，leading to high rejection rates．SW400 steel is a special high strength wheel steel developed by Benxi Steel．Taking SW400 steel as the research material，this article studys the feasibility of improving the properties of rim flash butt welded joints by adding preheating process．
The experiment of Nd:YAG pulsed laser self-fluxing welding for 304 stainless steel/Ti6Al4V titanium alloy dissimilar metal was carried out．The microstructure properties of welded joint were analyzed by SEM，EDS and XRD．The equilibrium lattice constants，enthalpies of formation，cohesive energies，mechanical properties，Debye temperatures and valence electron structures of Ti－Fe intermetallic compounds(IMCs)were calculated by the first principle pseudopotential plane wave method based on density functional theory(DFT)．According to the thermodynamic data of Ti－Fe－Cr compounds，the Gibbs free energy per mole of compound at different temperatures was calculated and their thermal stability was compared．The results show that there are no macroscopic cracks in the welded joints，and the IMCs distributed evenly along the welding interface exhibits 3 distinct layers of microstructure with different colors．The welds interface generates IMCs of TiFe，TiFe2and a small amount of Ti5Cr7Fe17IMCs．Ti－ Fe IMCs with high thermodynamic stability and easy alloying formation．The results of Gibbs free energies show that the sequence of precipitates in the interface is Ti5Cr7Fe17，TiFe2and TiFe in high temperature during the metallurgical reaction．The G/B values of Ti－ Fe IMCs are greater than the critical value of 0．5，indicating that it is an intrinsic brittleness．
This work mainly articulated the effects of nozzle structure on arc characteristics in gas pool coupled activating TIG(GPCA－TIG)welding process by using Fluent Software．Different models were set up to adapt the different torch structure during computer progress．The specific configuration of the welding torch made the gas flow in outer gas passage constrained．The nozzle structure has great influence on outer gas distribution because of the changing of coupling region between the outer active gas and molten pool surface．When the coupling degree is reduced or the outer gas passage become smaller，the oxygen in outer gas penetrates into the arc plasma and spreads to the arc region more easily．Owing to its cooling effects，the morphology of arc is contracted，and the arc temperature is increased．When the inner wall and the outer wall of outer gas passage are not parallel，the wide top and narrow bottom nozzle shape can bring more oxygen into the arc plasma，the arc is contracted and the peak temperature of arc rises a little more comparing to the narrow top and wide bottom one．
This paper presents a numerical simulation of deformation and residual stress in butt-weld joint for different shaped plates．Within the framework of numerical investigation，3 types of models and a double ellipsoidal heat source were implemented in finite element simulation．As for an effect of geometric shape，the weld-induced deformation and residual stress should be taken into account during designing the welded structure．And for U －shape plates，the effect of curvature radius on the mechanical properties was also obtained，which is a significant factor affecting its service life．The simulation results revealed that the plate processed into U-shape could reduce the deformation and residual stress near the weld．And the deformation and residual stress in U－shape plate with circular arc transition were further reduced．Furthermore，the effect of curvature radius on the mechanical properties of plates was not general considered as the bigger curvature radius the better mechanical properties．The results concluded that the geometric shape significantly affects the mechanical properties，which provides prediction for structural design．
In present paper，the metal vapour behavior in double electrodes TIG welding was investigated by a numerical model，including the arc plasma and weld pool．The thermodynamic parameters and transport coefficients of the arc plasma were dependent on both the local temperature and the mass ratio of the metal vapour．A second viscosity approximation was used to formulate the diffusion coefficient of the metal vapour in the arc plasma．The temperature and flow fields together with the metal vapour concentration were simulated，and the influences of metal vapour on the arc plasma and the weld pool were analyzed．It was found that the metal vapour transport in the arc plasma was significantly influenced by the flow of the arc plasma，and the distribution of the metal vapour was more extended in the direction perpendicular to the line through the double electrodes tips．Both the arc plasma and the heat flux at the weld pool were constricted by the presence of the metal vapour，while the metal vapour had a minor effect on the total heat input to the work piece and the weld pool profile as a whole．
The weld appearance，deposition rate，welding efficiency，stability of arc，laser keyhole characteristic，and weld property were studied by using a novel laser-MIG hybrid welding process with filling wire of aluminum alloy．The results were also compared with those by conventional laser-MIG hybrid welding process．It was found that with the suitable process parameters this novel welding process for aluminum alloy was stable and final weld bead had fine appearance．Compared to conventional laser-MIG hybrid welding process，during this novel welding process the stability of arc，the laser keyhole characteristic and the weld property were similar，while the keyhole cycle frequency and keyhole opening area had differences of 1．23%and 15．34%，respectively，and the welding efficiency increased by about 31%without increasing heat input．
In recent years，the research on pipeline laser-arc hybrid welding technology has been the important and difficult in the field of welding all over the world．China Petroleum Pipeline Research Institute Co．Ltd．has firstly developed pipeline laser-arc hybrid welding system in China，and executed the welding tests based on X70/X80 steel．Preliminary experiment results showed that hybrid welding could meet the requirements of related standards such as API1104，ASME，etc．，the mechanical properties of girth seam are qualified in the case that there were no internal defects．With the development of high-power fiber laser and the continuous improvement of welding equipment，laser-arc hybrid welding technology for pipeline field welding will be available soon．
In this paper，the performance of HG70D welded joint of ultra-high strength steel plates is presented，and the performance of HG70D and Q345B welded joints is studied．The high strength steel plate HG70D showed excellent weldability．Through the X －ray inspection of welded joints，tensile strength，impact test and bending performance test，the comprehensive performance of the joint was excellent．The macroscopic and microscopic metallographic analysises of the welded joints show that the welding seams included pearlite，sorbite，ferrite，etc．The influence of stress annealing temperature on HG70D of high strength steel plate was analyzed by heat treatment．
