A critical review on solid-state welding of high entropy alloys-processing,microstructural characteristics and mechanical properties of joints

The high entropy alloys(HEAs)are the newly developed high-performance materials that have gained significant importance in defence,nuclear and aerospace sector due to their superior mechanical properties,heat resistance,high temperature strength and corrosion resistance.These alloys are manufactured by the equal mixing or larger proportions of five or more alloying elements.HEAs exhibit superior mechanical performance compared to traditional engineering alloys because of the extensive alloying composition and higher entropy of mixing.Solid state welding(SSW)techniques such as friction stir welding(FSW),rotary friction welding(RFW),diffusion bonding(DB)and explosive welding(EW)have been efficiently deployed for improving the microstructural integrity and mechanical properties of welded HEA joints.The HEA interlayers revealed greater potential in supressing the formation of deleterious intermetallic phases and maximizing the mechanical properties of HEAs joints.The similar and dissimilar joining of HEAs has been manifested to be viable for HEA systems which further expands their industrial applications.Thus,the main objective of this review paper is to present a critical review of current state of research,challenges and opportunities and main directions in SSW of HEAs mainly CoCrFeNiMn and Al_xCoCrFeNi alloys.The state of the art of problems,progress and future outlook in SSW of HEAs are critically reviewed by considering the formation of phases,microstructural evolution and mechanical properties of HEAs joints.

Numerical analysis of arc-droplet behavior in thin wire high current MAG welding with magnetic control

High efficiency welding has always been one of the hot research subjects at home and overseas. Aiming at the problem of unstable droplet rotating spray transfer process in 450 A thin wire metal active gas arc(MAG) welding, a three-dimensional arc-droplet coupled model is established in this paper on the base of fluid dynamics to conduct numerical analysis for droplet transfer behavior with external magnetic controlled MAG welding, and used high-speed camera system to verify the simulation results. The results indicate that without external magnetic field, the droplet is transferred by the way of rotating spray, the arc is changeable and the spatter is serious. The electromagnetic force accelerates the radial liquid beam rotation under direct current(DC) magnetic field, and increases the angle between liquid beam and welding wire axis. Meanwhile, the rotation frequency of the liquid beam reaches 400 Hz, the area of arc column and heat loss increase under DC magnetic field. Based on the alternating magnetic field, the arc is the “bell shaped”, the arc stiffness raises, its temperature achieves 26 000 K, and the maximum speed of the liquid stream beam can reach 500 m/s. And the droplet transfer is more stable, the spatter significantly reduces, and welding quality is effectively improved.

Welding of nickel free high nitrogen stainless steel: Microstructure and mechanical properties

High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.

Numerical simulation and control of welding distortion for double floor structure of high speed train

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code.Then,the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software.The effects of welding sequence,clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically.The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure.Compared with the welding sequence,the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure.In the case of30 mm reverse deformation,the maximum deformation can be reduced about 70%in comparison to an actual welding process.

Microstructure and Wear Performance of High Volume Fraction Carbide M_7C_3 Reinforced Fe-based Composite Coating Fabricated by Plasma Transferred Arc Welding

The fabrication of high volume fraction （HVF） M7C3 （M=Cr, Fe） reinforced Fe-based composite coating on ASTM A36 steel plate using plasma transferred arc （PTA） welding was studied. The results showed that the volume fraction of carbide M7C3 was more than sixty percent, and the relative wear resistance of the coating tested on a block-on-ring dry sliding tester at constant load （100 N） and variable loads （from 100 to 300 N） respectively was about 9 and 14 times higher than that of non-reinforced a-Fe coating. In addition, under constant load condition the friction coefficients （FCs） of two coatings increased first and then decreased with increasing sliding distance. However, under variable loads condition the FCs of non-reinforced a-Fe based coating increased gradually, while that of HVF MTC3 reinforced coating decreased as the load exceeded 220 N. The worn surface of non-reinforced a-Fe based coating was easily deformed and grooved, while that of the HVF M7C3 reinforced coating was difficult to be deformed and grooved.

Application and development of friction stir welding technology in high speed EMU manufacturing

The application status of friction stir welding technology is introduced,and the application research of advanced FSW technology in the manufacture of high-speed electric multiple unit aluminum alloy body is analyzed,including the application of traditional friction stir welding technology to a combination of a lap joint and butt joint,and butt joint of large thick plate by both sides process,also introduces bobbin-tool friction stir welding to a butt joint and three-dimensional space curved friction stir welding to T-joint. At the same time the future development trend of new FSW technology derived from traditional FSW technology in rail vehicle manufacturing industry is put forward. As the fast developing of critical technology used on railway vehicles,quick applying advanced welding technology will affect products quality,manufacturing cost and production cycle time directly,and it certainly will be one of the approaches to develop markets by all the railway vehicles manufacturing enterprises.

Experimental determination of the critical welding speed in high speed MAG welding

In high speed MAG welding process, some weld formation defects may be encountered. To get good weld quality, the critical welding speed beyond which humping or undercutting weld bead can occur must be known for different conditions. In this research, high speed MAG welding tests were carried out to check out the effects of different factors on the critical welding speed. Through observing the weld bead profiles and the macrographs of the transverse sections of MAG welds, the occurrence tendency of humping weld was analyzed, and the values of critical welding speed were determined under different levels of welding current or voltage, and the effect of shielding gas compositions on the critical welding speed was also investigated.

WELDING BETWEEN HIGH MANGANESE STEEL AND HIGH CARBON STEEL

Manuscript received 30 July 1999 Abstract The shielded metal arc welding (SMAW) of a manganese steel part as a crossing of railway track to a carbon steel part as the rails of the railroad is the welding of dissimilar steel. It are was known that it is not possible to the the rail of railroad directly to the cross- ing of railway track made from a steel containing about 14% of manganese (wt. ) because of so many differences between the two kinds of steels such as composition, microstructure,mechanical properties and weldability.A method was used to solve the problem by presetting an intermediate layer on each side of the joint and other special procedures were used.The result of test indicated that a good weld joint was obtained.

Stability of fiber laser-MIG hybrid welding of high strength aluminum alloy

The effect of fiber laser on MIG arc was investigated with 8 mm 7075-T6 high strength aluminum alloy as base material.The arc shape,droplet transfer form and electrical signal in the process of MIG welding and laser-MIG hybrid welding were analyzed.The stability of the hybrid welding process was evaluated by standard deviation analysis.The results show that with the increase of laser power,a large number of laser-induced plasma enters the arc column area,providing more conductive channels,which makes the heat of MIG arc more concentrated and the short circuit transition disappear.Due to the continuous effect of laser,the keyhole becomes a continuous electron emission source,and a stable cathode spot will be formed near the keyhole,which enhances the stability of MIG arc at the base current state.By using the method of standard deviation analysis,the voltage standard deviation of single MIG welding arc and laser-MIG hybrid arc within 4 seconds was calculated.The standard deviation of single MIG arc voltage was 1.05,and the standard deviation of MIG arc voltage in laser-MIG hybrid welding was 0.71–0.86,so the hybrid welding process was more stable.

Implementation of high speed arc welding with DE-GMAW

Modern manufacturing industry demands low cost and high efficient welding processes to remain competitiveness in the time of globalization. In this study, conventional gas metal arc welding （GMAW） was modified, a double-electrode GMAW （DE-GMAW） system is developed and DE-GMAW process is implemented through optimization of the design and process parameters and suitable selection of igniting sequence of double arcs. High speed welding tests were carried out to examine the effects of different factors on occurrence of weld formation defects. Through observing the weld bead appearance in DE-GMA W, the values of critical welding speed were determined under different levels of welding current and welding speed.

Numerical simulation of residual stress and deformation for submerged arc welding of Q690D high strength low alloy steel thick plate

The finite element simulation software SYSWELD is used to numerically simulate the temperature field,residual stress field,and welding deformation of Q690D thick plate multi-layer and multi-pass welding under different welding heat input and groove angles.The simulation results show that as the welding heat input increases,the peak temperature during the welding process is higher,and the residual stress increases,they are all between 330–340 MPa,and the residual stress is concentrated in the area near the weld.The hole-drilling method is used to measure the actual welding residual stress,and the measured data is in good agreement with the simulated value.The type of post-welding deformation is angular deformation,and as the welding heat input increases,the maximum deformation also increases.It shows smaller residual stress and deformation when the groove angle is 40°under the same heat input.In engineering applications,under the premise of guaranteeing welding quality,smaller heat input and 40°groove angle should be used.

NUMERICAL SIMULATION OF TEMPERATURE FIELD ON FLASH BUTT WELDING FOR HIGH MANGANESE STEELS

An axial symmetry finite element model coupled with electricity-thermal effect was developed to study the temperature field distribution in process of the flash butt welding （FBW） of frog highmanganese steel. The influence of temperature dependent material properties and the contact resistance were taken into account in FEM ＇simulation. Meanwhile, the lost materials due to .splutter was resolved by using birth and death element. The result of analyzing data shows that the moddel in the FBW flashing is reasonable and feasible, and can exactly simulate the temperature field distribution. The modeling provides reference for analysis of welding technologies on the temperature field of high-manganese steel in FBW.

Prediction and Verification of Resistance Spot Welding Results of Ultra-High Strength Steels through FE Simulations

Resistance spot welding (RSW) is the most common welding method in automotive engineering due to its low cost and high ability of automation. However, physical weldability testing is costly, time consuming and dependent of supplies of material and equipment. Finite Element (FE) simulations have been utilized to understand, verify and optimize manufacturing processes more efficiently. The present work aims to verify the capability of FE models for the RSW process by comparing simulation results to physical experiments for materials used in automotive production, with yield strengths from approximately 280 MPa to more than 1500 MPa. Previous research has mainly focused on lower strength materials. The physical weld results were assessed using destructive testing and an analysis of expulsion limits was also carried out. Extensive new determination of material data was carried out. The material data analysis was based on physical testing of material specimens, material simulation and comparison to data from literature. The study showed good agreement between simulations and physical testing. The mean absolute error of weld nugget size was 0.68 mm and the mean absolute error of expulsion limit was 1.10 kA.

Development of high frequency pulse power source using two powersfor TIG welding

A high frequency pulse power source for TIG welding is developed. The structure of two powers is adopted. The by pass circuit effectively eliminates the effect of the cable equivalent inductance. The maximum frequency of the output pulse current reaches to 16 kHz . The base current and the peak current can be regulated separately.

High-speed butt welding of magnesium alloy using pulsed laser-arc hybrid heat source

Laser-arc hybrid welding at a speed of 6 000 mm/min is carried out on 2 mm thick magnesium alloy AZ61 plateand completely-penetrated butt joints are obtained, lnvestigations of the influence of parameters on weld formation show that Ihe addition of pulsed laser can effctively enhance tlle heat penetrability attd directivity nf the hybrid heat source. Measurements on microstructures and mechanical properties the joint indicate that grain in the.fhsion zone is refined and the grain size is sensitive to the arc current ; the fitsioa zone exhibits the highest hardaess; the tensile strength of the joint reaches 93% of base metal; there is the brittle fracture along the grain bozmdaries in the fusion zone. High-speed camera images exhibit that although the two adjacent laser pulses can not overlap, the recorery relaxation of the concentrated electric arc after laser intlse action can still maintain the continuous welding process.

Experimental study of weld position detection based on keyhole infrared image during high power fiber laser welding

Keyhole is one of the important phenomena in high-power laser welding process. By studying the keyhole characteristic and detecting the seam offset during high-power fiber laser welding, an infrared sensitive high-speed camera arranged off-axis orientation of laser beam was applied to capture the dynamic thermal images of a molten pool. The 304 austenitic stainless steel plate butt joint welding experiment with laser power 10 kW was carried out. Through analyzing the keyhole infrared image, the weld position was calculated. Least squares method was used to determine the actual weld position. Image filtering technique was used to process the keyhole image, and the keyhole centroid coordinate were calculated. Also, least squares method was used to fit the keyhole centroid curve equation and establish a nonlinear continuous model which described the deviation between keyhole centroid and weld seam. The heat accumulation effect affected by the infrared radiation was analyzed to determine whether the laser beam focus spot deviated from the desired welding seam. Experimental results showed that the keyhole centroid has related to the seam offset, and can reflect the welding quality.

Formation mechanism of transverse crack in repair welding for thick plate of Q345 high strength steel

Transverse cracks occur usually in repair welding for thick plate of high strength steel. It needs multiple times of repair welding. The quality of production and deliver deadline will be influenced. Therefore, it is very significant to investigate the cause and control of transverse crack in repair welding. In this paper, both ends restraint crack experiment is developed to produce delay transverse crack for high strength steel. Metallographic results show that four types of cracks are found in repair welding metal zone and heat affected zone. Large chevron transverse cracks are found in repair welding zone. Lots of micro transverse cracks are found in inter-layer repair welding metal zone, root HAZ and two ends of repair welding individually. The distribution character and formation mechanism of the transverse crack are further analyzed through hardness testing and residual stress measurement.

Effect of welding processes on mechanical and microstructural characteristics of high strength low alloy naval grade steel joints

Naval grade high strength low alloy(HSLA) steels can be easily welded by all types of fusion welding processes. However, fusion welding of these steels leads to the problems such as cold cracking, residual stress, distortion and fatigue damage. These problems can be eliminated by solid state welding process such as friction stir welding(FSW). In this investigation, a comparative evaluation of mechanical(tensile, impact,hardness) properties and microstructural features of shielded metal arc(SMA), gas metal arc(GMA) and friction stir welded(FSW) naval grade HSLA steel joints was carried out. It was found that the use of FSW process eliminated the problems related to fusion welding processes and also resulted in the superior mechanical properties compared to GMA and SMA welded joints.

Study on welding process performance of HG70D high strength steel plate

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.

Characteristics of the electrode melting phenomena in narrow gap MAG high-rotating-speed arc welding

The influence of rotating speed on metal transfer and the wire metal speed was studied in the high rotating speed arc narrow gap welding.The results indicate that the high rotating speed arc has benefit on the metal transfer,and that with the rotating speed increasing,the droplet volume decreases.It is shown that the rotating speed has little influence on the wire metal speed with DC electrode positive polarity(DCEP),but the melting speed decreases with increasing of rotating speed in DC electrode negative polarity(DCEN).