Recent research progress in the mechanism and suppression of fusion welding-induced liquation cracking of nickel based superalloys

Nickel-based superalloys are extensively used in the crucial hot-section components of industrial gas turbines,aeronautics,and astronautics because of their excellent mechanical properties and corrosion resistance at high temperatures.Fusion welding serves as an effective means for joining and repairing these alloys;however,fusion welding-induced liquation cracking has been a challenging issue.This paper comprehensively reviewed recent liquation cracking,discussing the formation mechanisms,cracking criteria,and remedies.In recent investigations,regulating material composition,changing the preweld heat treatment of the base metal,optimizing the welding process parameters,and applying auxiliary control methods are effective strategies for mitigating cracks.To promote the application of nickel-based superalloys,further research on the combination impact of multiple elements on cracking prevention and specific quantitative criteria for liquation cracking is necessary.

Design of Fully Automatic Specification Selection System for Resistance Welding Equipment

A system for fully automatic selection of welding specifications in resistance welding equipment has been developed to address the problem of workers frequently choosing the wrong specifications during manual welding of multiple parts on a single machine in automobile factories. The system incorporates an automatic recognition system for different workpiece materials using the added machine fixture,visual detection system for nuts and bolts,and secondary graphical confirmation to ensure the correctness of specification calling. This system achieves reliable,fully automatic selection of welding specifications in resistance welding equipment and has shown significant effects in improving welding quality for massproduced workpieces,while solving the problem of specification calling errors that can occur with traditional methods involving process charts and code adjustments. This system is particularly suitable for promoting applications in manual welding of multiple parts on a single machine in automobile factories,ensuring correct specification calling and welding quality.

Theoretical analysis of the elastic Kelvin-Helmholtz instability in explosive weldings

By considering the joint effects of the Kelvin-Helmholtz(KH) and Rayleigh-Taylor(RT) instabilities, this paper presents an interpretation of the wavy patterns that occur in explosive welding. It is assumed that the elasticity of the material at the interface effectively determines the wavelength, because explosive welding is basically a solid-state welding process. To this end, an analytical model of elastic hydrodynamic instabilities is proposed, and the most unstable mode is selected in the solid phase. Similar approaches have been widely used to study the interfacial behavior of solid metals in high-energy-density physics. By comparing the experimental and theoretical results, it is concluded that thermal softening,which significantly reduces the shear modulus, is necessary and sufficient for successful welding. The thermal softening is verified by theoretical analysis of the increase in temperature due to the impacting and sliding of the flyer and base plates, and some experimental observations are qualitatively validated.In summary, the combined effect of the KH and RT instabilities in solids determines the wavy morphology, and our theoretical results are in good qualitative agreement with experimental and numerical observations.

Effect of process parameters on the morphology of aluminum/copper alloy lap joints by red and blue hybrid laser welding

In order to overcome the problems of many pores,large deformation and unstable weld quality of traditional laser welded aluminumcopper alloy joints,a red-blue dual-beam laser source and a swinging laser were introduced for welding.T2 copper and 6063 aluminum thin plates were lap welded by coaxial dual-beam laser welding.The morphology of weld cross section was compared to explore the influence of process parameters on the formation of lap joints.The microstructure characteristics of the weld zone were observed and compared by optical microscope.The results show that the addition of laser beam swing can eliminate the internal pores of the weld.With the increase of the swing width,the weld depth decreases,and the weld width increases first and then decreases.The influence of welding speed on the weld cross section morphology is similar to that of swing width.With the increase of welding speed,the weld width increases first and then decreases,while the weld depth decreases all the time.This is because that the red laser is used as the main heat source to melt the base metals,with the increase of red laser power,the weld depth increases.As an auxiliary laser source,blue laser reduces the total energy consumption,consequently,the effective heat input increases and the spatter is restrained effectively.As a result,the increase of red laser power has an enhancement effect on the weld width and weld depth.When the swing width is 1.2 mm,the red laser power is 550 W,the blue laser power is 500 W,and the welding speed is 35 mm/s,the weld forming is the best.The lap joint of T2 copper and 6063 aluminum alloy thin plate can be connected stably with the hybrid of blue laser.The effect rules of laser beam swing on the weld formation were obtained,which improved the quality of the joints.

Intermetallic Compounds Formation in Dissimilar Friction Stir Welding of Mg/Cu Alloys

Joining dissimilar Mg/Cu alloys was still an intractable problem because of the excessive intermetallic compounds(IMCs)and poor mechanical properties using conventional welding methods.In the present study,friction stir welding was employed for the butt joining of dissimilar AZ31B Mg-alloy and T2 pure Cu plates.Defect-free Mg/Cu joints were obtained with Mg-RS and Cu-AS configuration,at a welding speed of 50 mm/min and tool rotating speeds of 325 r/min,625 r/min and 925 r/min.At the joining interface,both Mg_(2)Cu and MgCu_(2) IMC phases were observed,with a clear,uniform and continuous IMCs layer composed of two sub-layers,layer-A of Mg+Mg_(2)Cu and layer-B of Mg_(2)Cu+MgCu_(2).The maximum ultimate tensile strength of the Mg/Cu friction stir welding joint reached 130 MPa at 925 r/min due to enhanced mechanical interlocking between Mg and Cu,as well as sufficient metallurgical bonding at the joining interface with an IMCs layer thickness in the range of 1.0-2.0μm.

A review of linear friction welding of Ni -based superalloys

Ni-based superalloys are one of the most important materials employed in high-temperature applications within the aerospace and nuclear energy industries and in gas turbines due to their excellent corrosion,radiation,fatigue resistance,and high-temperature strength.Linear friction welding(LFW)is a new joining technology with near-net-forming characteristics that can be used for the manu-facture and repair of a wide range of aerospace components.This paper reviews published works on LFW of Ni-based superalloys with the aim of understanding the characteristics of frictional heat generation and extrusion deformation,microstructures,mechanical proper-ties,flash morphology,residual stresses,creep,and fatigue of Ni-based superalloy weldments produced with LFW to enable future optim-um utilization of the LFW process.

MD Simulation of Diffusion Behaviors in Collision Welding Processes of Al-Cu, Al-Al, Cu-Cu

To investigate the effects of material combinations and velocity conditions on atomic diffusion behavior near collision interfaces,this study simulates the atomic diffusion behavior near collision interfaces in Cu-Al,Al-Al and Cu-Cu combinations fabricated through collision welding using molecular dynamic(MD)simulation.The atomic diffusion behaviors are compared between similar metal combinations(Al-Al,Cu-Cu)and dissimilar metal combinations(Al-Cu).By combining the simulation results and classical diffusion theory,the diffusion coefficients for similar and dissimilar metal material combinations under different velocity conditions are obtained.The effects of material combinations and collision velocity on diffusion behaviors are also discussed.The diffusion behaviors of dissimilar material combinations strongly depend on the transverse velocity,whereas those of the similar material combinations are more dependent on the longitudinal velocity.These findings can provide guidance for optimizing welding parameters.

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.

3D modeling for effect of tool eccentricity on coupled thermal and material flow characteristics during friction stir welding

A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical boundary condition at the tool-workpiece interface,and the dynamic mesh technique are both employed for the consideration of the tool eccentricity during tool rotating.It is found that tool eccentricity induces the periodical variation of the heat densities both at the tool-workpiece interface and inside the shear layer,but the fluctuation amplitudes of the heat density variations are limited.However,it is demonstrated that tool eccentricity results in significant variation of the material flow behavior in one tool rotating period.Moreover,the material velocity variation at the retreating side is particularly important for the formation of the periodic characteristics in FSW.The modeling result is found to be in good agreement with the experimental one.

Influence of heat input on microhardness and microstructure across the welding interface between stainless steel and low alloy steel

The welding interface is crucial to the service safety of dissimilar metal weld(DMW)joints between stainless steel(SS)and low alloy(LA)steel.Different status of welding interfaces was prepared by cladding SS consumables to LA steel substrates with different heat inputs via tungsten inert gas arc welding(TIG),followed by a series of microstructural characterizations and hardness tests.Results showed that a hardening and transition layer(TL)would be generated along the welding interface,and the width and hardening degree of the TL would increase with the heat input.Meanwhile,heavy load hardness tests showed that highly severe inhomogeneous plastic deformation and the microcrack would be generated in the interfacial region and the welding interface respectively in the highest heat input sample(1.03 kJ/mm).These results indicate that the increase in heat input would deteriorate the bonding performance of DMW joints.Further microstructural observations showed that the higher hardening degree of the highest heat input sample was mainly attributed to the stronger grain boundary,solution,and dislocation strengthening effects.

Bulging Distortion of Austenitic Stainless Steel Sheet on the Partially Penetrated Side of Non-Penetration Lap Laser Welding Joint

Non-penetration laser welding of lap joints in austenitic stainless steel sheets is commonly preferred in fields where the surface quality is of utmost importance.However,the application of non-penetration welded austenitic stainless steel parts is limited owing to the micro bulging distortion that occurs on the back surface of the partial penetration side.In this paper,non-penetration lap laser welding experiments,were conducted on galvanized and SUS304 austenitic stainless steel plates using a fiber laser,to investigate the mechanism of bulging distortion.A comparative experiment of DC01 galvanized steel-Q235 carbon steel lap laser welding was carried out,and the deflection and distortion profile of partially penetrated side of the sheets were measured using a noncontact laser interferometer.In addition,the cold-rolled SUS304 was subjected to heat holding at different temperatures and water quenching after bending to characterize its microstructure under tensile and compressive stress.The results show that,during the heating stage of the thermal cycle of laser lap welding,the partial penetration side of the SUS304 steel sheet generates compressive stress,which extrudes the material in the heat-affected zone to the outside of the back of the SUS304 steel sheet,thereby forming a bulge.The findings of these experiments can be of great value for controlling the distortion of the partial penetrated side of austenitic stainless steel sheet during laser non-penetration lap welding.

Effect of V content on microstructures and properties of TiC cermet fusion welding interface

The effects of vanadium(V)on the microstructures and mechanical properties of the TiC cermet fusion welding interface were studied by adjusting the content of V in the self-developed flux-cored wires using metal inert gas arc(MIG)welding for surfacing on the TiC cermet.The results show that the increase in V content promotes the element diffusion between TiC cermet and weld metal.There are no de-fects observed in the interface,and the diffusion of elements refers to excellent metallurgical bonding.The shear strength of the fusion zone initially decreases and then increases with the increase in V content.The maximum shear strength of the TiC cermet/weld interface,reaching 552 MPa,occurred when the V content reached 0.65%.Meanwhile,the average hardness in the transition zone reached 488.2 HV0.2.

Temperature field calculation of rail flash welding

The forging stage of rail flash welding has a decisive influence on joint strength,and the study of the temperature distribution in the process has an important role in further improving joint strength.In this paper,three calculation methods for the temperature field are given.First,the finite element model of the temperature field before forging rail flash welding is established by using the transient heat module of Ansys software and verified by infrared temperature measurement.Second,the temperature distribution of different parts of the rail before flash welding is obtained by using infrared thermal imaging equipment.Third,Matlab software is used to calculate the temperature of the non-measured part.Finally,the temperature distribution function along the rail axis is fitted through the temperature measurement data.The temperature distribution before the top forging of the rail flash welding can be used to analyze the joint and heat-affected zone organization and properties effectively and to guide the parameter setting and industrial production.

Metallurgical Microstructure Complexity in the Electron Beam Welding (EBW) Joint of Ti6246

Electron Beam Welding (EBW) is employed to both melt and unite materials, influencing their thermal history and subsequently determining the microstructure and properties of the welded joint. Welding Titanium alloys involves undergoing local melting and rapid solidification, subjecting the material to thermal stresses induced by a thermal expansion coefficient of 9.5 × 10 m/m°C. This process, reaching range temperatures from the full melting alloy to room temperature, results in phase formation dictated by the thermodynamic preferences of the alloyed elements, posing a significant challenge. Recent efforts in simulation and calculations have been undertaken elsewhere to address this challenge. This study focuses on a joint of two plates with differing cross-sectional areas, influencing heat transfer during welding. This report presents a case study focusing on the metallurgical changes observed in the microstructure within the welded zone, emphasizing alterations in the cooling rate of the welded joint. The investigation utilizes optical metallography, Vickers’s Hardness testing, and SEM (scanning electron microscopy) to comprehensively characterize the observed changes in addition to heat transfer simulation of the welded zone.

新时代背景下焊接专业全英文课程建设与改革实践——以《Solid State Welding》为例

在全球国际化和国家战略“双一流”建设的背景下,积极构建焊接技术与工程专业或焊接方向的国际化人才培养体系与模式,大力推进全英文课程的建设与改革,加快培养焊接领域国际化综合人才具有十分重要的意义。课程建设与改革是新工科建设的实施途径,文中以《Solid State Welding》全英文课程实践为例,不断完善新工科焊接方向课程体系建设,构建与国际接轨的教学内容与方法,将国际化视野、国际化教学思维及方法融入到全英文教育教学中,使学生在掌握国际课程知识的基础上,开拓国际视野,有效培养国际交流与合作能力。

Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

Analysis of Aluminum Alloy Double-Pulse MIG Welding Arc Signal Characteristics Based on Broadband Mode Decomposition

Welding voltage and current in arc signals are directly related to arc stability and welding quality.Process experiments with different parameters were organized according to the orthogonal experimental design method by constructing an aluminum alloy double-pulse metal inert gas(MIG)welding arc electric signal test platform.The data acquisition system of the aluminum alloy MIG welding process was established to obtain real-time arc signal information reflecting the welding process.The aluminum alloy’s collected double-pulse arc current signals are decomposed adaptively by broadband mode decomposition(BMD).The direct current(DC)signal,pulse signal,distortion signal,ripple signal,and noise signal are separated and extracted,and the composite multiscale fuzzy entropy(CMFE)is calculated for the component set of the electrical signal.The experimental results show that the current waveform obtained by the double-pulse MIG welding current signal is consistent with the corresponding weld forming diagram.Simultaneously,the composite multiscale fuzzy entropy is calculated for the arc characteristic parameters.The rationality of matching process parameters and arc stability of aluminum alloy’s double-pulse MIG welding were evaluated.

基于Simufact Welding的等高齿弧锥齿轮铣刀盘焊接数值模拟

利用Simufact Welding焊接仿真软件对等高齿弧锥齿轮铣刀盘的焊接进行模拟仿真。通过改变焊接坡口间隙进行变量控制,使用激光填丝多层单道焊接方法在其他焊接参数相同条件下进行焊接,得到坡口间隙为2mm时焊接变形量与残余应力最小的结论。

基于Simufact Welding的激光熔覆仿真研究

激光熔覆是利用高能量光束将合金粉末通过预设轨迹将受损零件修复成完整状态的一项新兴技术,粉末在经高能激光照射后变为熔融状态,熔覆层与基体结合,基体的材料性能便得以提升。基于钛合金强度高的特点,以Ti-6Ai-V粉末为研究对象,利用Simufact Welding对Ti-6AI-4V粉末进行激光熔覆仿真,并通过单道激光熔覆仿真研究激光熔覆过程中激光功率、扫描速度、初始温度对熔覆的影响规律,同时比较激光功率、扫描速度、初始温度对熔池温度变化速率的影响。

Achieving a high-strength dissimilar joint of T91 heat-resistant steel to 316L stainless steel via friction stir welding

The reliable welding of T91 heat-resistant steel to 316L stainless steel is a considerable issue for ensuring the safety in service of ultrasupercritical power generation unit and nuclear fusion reactor,but the high-quality dissimilar joint of these two steels was difficult to be obtained by traditional fusion welding methods.Here we improved the structure-property synergy in a dissimilar joint of T91 steel to 316L steel via friction stir welding.A defect-free joint with a large bonding interface was produced using a small-sized tool under a relatively high welding speed.The bonding interface was involved in a mixing zone with both mechanical mixing and metallurgical bonding.No obvious material softening was detected in the joint except a negligible hardness decline of only HV~10 in the heat-affected zone of the T91 steel side due to the formation of ferrite phase.The welded joint exhibited an excellent ultimate tensile strength as high as that of the 316L parent metal and a greatly enhanced yield strength on account of the dependable bonding and material renovation in the weld zone.This work recommends a promising technique for producing high-strength weldments of dissimilar nuclear steels.