基于工件与外部可消耗工具摩擦的焊接技术研究进展

摩擦焊是一类依靠摩擦产热来实现材料连接的固相焊接技术,具有接头质量高、焊接变形小、节能环保等优点,广泛应用于航空航天、交通运输、矿山机械、海洋装备等领域.近年来,摩擦焊技术发展迅速,一些改型的工艺相继产生.根据相互摩擦对象的属性对摩擦焊技术进行了分类,归纳了各自的主要工艺特点.对基于工件与外部可消耗工具相互摩擦的焊接技术进行了系统综述,重点介绍了径向摩擦焊、摩擦-铆接、摩擦塞补焊、摩擦堆焊和涡流搅拌摩擦焊的基本工艺原理和最新研究进展,同时对以上工艺技术的未来发展展开了讨论,以期为相关领域的科研工作者提供参考.

Effect of Ca addition on the microstructure and the mechanical properties of asymmetric double-sided friction stir welded AZ61 magnesium alloy

The effects of 2%Ca addition on the microstructure and the mechanical properties of the asymmetric double-sided friction stir welded magnesium alloy AZ61 were investigated.Compared to the Ca-free AZ61magnesium alloy,the addition of 2%Ca significantly refines the grains in the stir zone after welding.Due to the existence of thermally stable Al2Ca particles,there is no noticeable change in the grain size in the stir zone regardless of the welding heat input.The electron backscattered diffraction analysis at the center of the stir zone confirmed the significant deterioration of the(0001)texture strength from the addition of 2%Ca.The tensile test of the joint suggested that the addition of 2%Ca provides stable tensile properties to the joint regardless of the welding parameters.The critical(0001)texture strength that determines the ultimate tensile strength decreased from 20 to 15 by the Ca addition.The addition of Ca enhanced the deterioration of the plastic elongation when the(0001)texture strength increased.

Time Dependant Weld Shape in Ar-O_2 Shielded Stationary GTA Welding

The stationary gas tungsten arc welding （GTA） is carried out on SUS304 stainless steel under Ar-0.1%O2 and Ar-0.3%O2 mixed shielding to observe the evolution of the molten pool and investigate the role of Marangoni convection on the weld shape. After welding, the oxygen content in the weld metal was measured by using an oxygen/nitrogen analyzer. Small addition of oxygen to the argon based shielding gas can effectively adjust the weld pool oxygen content. Oxygen plays an important role as an surface active element in determining the pattern of Marangoni convection in the stainless steel weld pool. When the weld metal oxygen content is over the critical value, 0.01 wt pct, corresponding to the Ar-0.3%O2 mixed shielding gas, the Marangoni convection changes from outward to inward direction and the weld shape dramatically changes from wide shallow shape to narrow deep shape.

Effect of the processing route on the microstructure and mechanical behavior of superlight Mg-9Li-1Zn alloy via friction stir processing

In this study, the effect of the processing route using a friction stir processing(FSP) method on the microstructure and mechanical behavior of a Mg-9Li-1Zn alloy was systematically investigated. In the FSP method, the odd-numbered(1st and 3rd) process directions and even-numbered(2nd and 4th) passes were alternated to distribute the strain throughout the whole processed zone uniformly. Consequently, the processed zone had a much more uniform microstructure and hardness distribution than the processed zone obtained using the conventional FSP method. Using this method, the grain size of a Mg-9Li-1Zn sheet alloy was refined from ~31 μm to ~0.21 μm with uniformly distributedα and β phases. The processed alloy exhibited a high strength-ductility synergy with an ultimate tensile strength(UTS) of 220.1 MPa and total elongation of 70.0% at a strain rate of 10^(-3)s^(-1), overwhelmingly higher than those of the base metal, 155.6 MPa in UTS and 36.0%in elongation. The in-situ SEM-DIC analysis and TEM observation demonstrated that such an outstanding ductility with moderate strength is caused by grain boundary sliding, the dominant deformation mechanism of the ultra-fine-grained sample after FSP. The processing route with reverse processing direction was proven to be efficient in producing the ultrafine grain size microstructure and improving the mechanical properties of superlight Mg-9Li-1Zn alloy.

Challenge to Welding and Joining Technology for Applying Multi-material in Electric Vehicle Production

Advanced high strength steel,aluminum alloy and plastic materials are used in the right places for the purpose of reducing the weight of EV(electric vehicle)bodies and in-vehicle parts,and multi-material structures are advancing.Therefore,it is difficult to handle the welding and joining processes of automobile structures by the conventional arc welding and resistance spot welding,which have been applied to steel joining,and various joining processes are being applied depending on the material.Under above mentioned background,the authors have developed some unique joining processes for multi-materials that are used in the right place.This paper introduces the dissimilar metal joining between the galvanized steel and aluminum alloy by laser arc hybrid process,the metal/thermoplastic dissimilar material joining using laser process and the solid-state resistance spot joining process of advanced high strength steel for EV body structural parts.Moreover,the authors describe the high-speed plasma jet GTA(Gas Tungusten Arc)welding process of copper applied to electrical components such as motors.

Principle for obtaining high joint quality in dissimilar friction welding of Ti-6Al-4V alloy and SUS316L stainless steel

Ti-6Al-4V alloy(Ti64)and SUS316 L stainless steel rods were dissimilarly friction welded.Especially focusing on the detailed observation of interface microstructural evolution during the friction welding(FW),the relationship between the processing conditions,weld interface microstructure,and mechanical properties of the obtained joints were systematically investigated to elucidate the principle for obtaining a high joint quality in the FW of Ti64 and SUS316L.A higher friction pressure produced a lower welding temperature in the FW,hence suppressing the thick intermetallic compound layer formation.However,hard and brittle Ti64/SUS316L mechanically mixed layers generally formed especially at the weld interface periphery due to the high temperature increasing rate,high rotation linear velocity and high outward flow velocity of the Ti64.These harmful layers tended to induce the cracks/voids formation at the weld interfaces hence deteriorating the joints’mechanical properties.The rotation speed reduction and liquid CO2 cooling during the entire processing decreased the temperature increasing rate,rotation linear velocity and outward flow velocity of the Ti64 at the weld interface periphery.Therefore,they suppressed the formation of the harmful mechanically mixed layers,facilitated the homogeneous and sound interface microstructure generation,and finally produced a high-quality dissimilar joint in the FW of Ti64 and SUS316L.

Weld Shape Variation and Electrode Oxidation Behavior under Ar-(Ar-CO_2) Double Shielded GTA Welding

Double shielded gas tungsten arc welding （GTAW, also known as tungsten inert gas （TIG） welding） of an SUS304 stainless steel with pure inert argon as the inner layer shielding and the At-CO2 or CO2 active gas as the out layer shielding was proposed in this study to investigate its effect on the tungsten electrode protection and the weld shape variation. The experimental results showed that the inner inert argon gas can successfully prevent the outer layer active gas from contacting and oxidizing the tungsten electrode during the welding process. Active gas, carbon dioxide, in the outer layer shielding is decomposed in the arc and dissolves in the liquid pool, which effectively adjusts the active element, oxygen, content in the weld metal. When the weld metal oxygen content is over 70×10-6, the surface-tension induced Marangoni convection changes from outward into inward, and the weld shape varies from a wide shallow one to a narrow deep one. The effect of the inner layer gas flow rate on the weld bead morphology and the weld shape was investigated systematically. The results show that when the flow rate of the inner argon shielding gas is too low, the weld bead is easily oxidized and the weld shape is wide and shallow. A heavy continuous oxide layer on the liquid pool is a barrier to the liquid pool movement.

Effect of Stacking Fault Energy on the Grain Structure Evolution of FCC Metals During Friction Stir Welding

The effect of stacking fault energy(SFE) on the grain structure evolution of face-centered cubic metals during friction stir welding was investigated by using pure aluminum,pure copper and Cu-30 Zn alloy as experiment materials.Tool "stop action" and rapid cooling were employed to "freeze" the microstructure of the flowing materials around the tool.Marker materials were used to show the streamline of the material flow.The microstructures of the three materials at different welding stages were contrastively studied by the electron backscatter diffraction technique.The results show that at the material flow stage,as the SFE decreases,the grain structure evolution changes from the continuous dynamic recrystallization to discontinuous dynamic recrystallization,and further to the dynamic equilibrium between the annealing twinning due to thermally activated grain boundary migration and the twin destruction during the plastic deformation.Owing to different grain structure evolution mechanisms,the grain structure at the end of the material flow is greatly different.Especially in copper,a lot of dislocations remain,which gives rise to the static recrystallization occurring during the subsequent cooling stage.

Flat friction spot joining of aluminum alloy to carbon fiber reinforced polymer sheets:Experiment and simulation

The Al alloy and carbon fiber reinforced polymer(CFRP)hybrid structures,incorporating the performance advantages of the two materials,have been attracting more attention in high-end manufacturing fields.In the current investigation,the flat friction spot joining(FSJ)was employed in joining the AA6061-T6 alloy and CFRP sheets.The significance of temperature distribution in influencing joint quality was highlighted through analyzing interface microstructural features,weld defect formation as well as fractography.To understand the role of thermal energy generation and conduction in the process comprehensively,a 3D thermal-mechanical coupling finite element model was established.The interfacial temperature was characterized by an uneven distribution behavior due to the inhomogeneous heat distribution.The peak temperatures on the top surface and Al alloy to CFRP interface at 1500 rpm rotational speed with 0.1 mm/s plunging speed were 498℃and 489°C,respectively.The peak interface temperature was reduced to286℃at 250 rpm,which produced an extremely small melted area.Compared with the plunging speed,rotational speed was found to be the predominant parameter for determining the joint property,which could be optimized to simultaneously realize the avoidance of thermal decomposition of CFRP,the sufficient melting duration time,and the wide enough melted area.Simulated thermal histories and melted area profiles were in agreement with experimental ones.The findings could be utilized to provide some feasible guidance for process optimization of dissimilar FSJ of metals and composites.

Interface strengthening in dissimilar double-sided friction stir spot welding of AZ31/ZK60 magnesium alloys by adjustable probes

Dissimilar welding of AZ31/ZK60 magnesium alloys with a thickness of 2 mm was successfully carried out by the double-sided friction stir spot welding with adjustable probes.A dissimilar joint bearing flat surfaces on both sides without a keyhole was obtained and the shear failure load of 8.7±0.5 kN was reached.The role of the adjustable probes has been revealed in detail.In the center of the stir zone,the welding interface structure was heterogeneous around which some distinct oxides still remained,leading to a weak interface strength.On the contrary,the welding interface structure around the shoulder/probe interface was homogeneous with no oxides giving rise to a strong interface strength,which is attributed to the severe material flow introduced by the adjustable probes.In addition,the vicinity outside the shoulder/probe interface,where the fracture occurred during the shear tensile tests,was also strengthened owing to the shearing and torsion by the adju stable probes.Therefore,a stable plug failure can be obtained and the joint properties can be improved.

Improving toughness of medium-Mn steels after friction stir welding through grain morphology tuning

This work demonstrated the viability of friction stir welding for the welding of medium-Mn steels when used as cryogenic vessel materials for liquefied gas storage.We used an intercritically annealed Fe-7 Mn-0.2 C-3 Al(wt.%)steel with a dual-phase(α'martensite andγ_(R) retained austenite)nanolaminate structure as a base material and systematically compared its microstructure and impact toughness after friction stir and tungsten inert gas welding.The friction stir welded specimen exhibited a large amount ofγ_(R) phase owing to a relatively low temperature during welding,whereas the tungsten inert gas welded specimen comprised only theα'phase.Furthermore,the friction stir welded steel exhibited a tuned morphology of nanoscale globular microstructure at the weld zone and did not exhibit any prior austenite grain boundary due to active recrystallization caused by deformation during welding.The preserved fraction ofγ_(R) and morphological tuning in the weldment improved the impact toughness of the friction stir welded steel at low temperatures.In the steel processed by tungsten inert gas welding,the notch crack propagated rapidly along the prior austenite grain boundaries-weakened by Mn and P segregations-resulting in poor impact toughness.However,the friction stir welded steel exhibited a higher resistance against notch crack propagation due to the slow crack propagation along the ultrafine ferrite/ferrite(α/α)interfaces,damage tolerance by the active transformation-induced plasticity from the large amount ofγR,and enhanced boundary cohesion by suppressed Mn and P segregations.