焊接参数对铁素体不锈钢搅拌摩擦焊接头组织及性能的影响

对4mm厚T4003铁素体不锈钢进行搅拌摩擦焊接工艺实验,研究焊接参数对接头组织特征、硬度分布及常温和低温冲击韧性的影响。结果表明:接头搅拌区和热力影响区由铁素体和马氏体双相组织构成;接头搅拌区组织沿试样厚度方向存在非均质性,且随转速的降低及焊接速率的增加越发显著;转速从150r/min增加至250r/min,前进侧热力影响区组织呈现小梯度过渡趋势,无明显变形拉长特征。焊缝硬度分布相对均匀,其最高硬度为290HV,约为母材的1.87倍。焊接参数和温度对接头的冲击吸收功有较大影响:常温(20℃)下,热影响区为母材的90%～92%,搅拌区为母材的85%～103%;低温(-20℃)下,热影响区为母材的87%～97%,搅拌区为母材的82%～95%,表明焊缝区仍具有较好强韧匹配。     

Mechanical properties and microstructure of friction stir welded tailor-made blanks

This paper studies the microstructural features and mechanical properties of friction stir welds with dissimilar alloys and different thicknesses. The welds are produced in five different thickness/material combinations from 2024-T3 and 7075-T6 sheets with different thicknesses. A parametric study is conducted to optimize the welding parameters such that the different configurations can be compared. The paper is divided into two chapters: microstructural features and mechanical properties. In the first chapter, a study of the chemical composition and microstructure of the welds shows that a narrow chemical mixing zone is present in the dissimilar-alloy welds and that the stirring zone embodies the union rings and exhibits heterogeneous texture for most configurations. Study of the hardness, tensile properties and fracture surfaces in the second chapter shows that an asymmetric softened region, which is harder at the advancing side and extends more into the retreating side, is formed in the stirring zone and that the mechanical properties decrease as the thickness ratio increases. The fracture was partially ductile and partially brittle for all configurations.     

Microstructures and mechanical properties of friction stir welds on 9% Cr reduced activation ferritic/martensitic steel

In this study,the microstructures and mechanical properties of 9%Cr reduced activation ferritic/martensitic(RAFM) steel friction stir welded joints were investigated.When a W-Re tool is used,the recommended welding parameters are 300 rpm rotational speed,60 mm/min welding speed and10 kn axial force.In stir zone(SZ),austenite dynamic recrystallization induced by plastic deformation and the high cooling rates lead to an obvious refinement of prior austenite grains and martensite laths.The microstructure in SZ contains lath martensite with high dislocation density,a lot of nano-sized MX and M_3C phase particles,but almost no M_(23)C_6 precipitates.In thermal mechanically affect zone(TMAZ)and heat affect zone(HAZ),refinement of prior austenite and martensitic laths and partial dissolution of M_(23)C_6 precipitates are obtained at relatively low rotational speed.However,with the increase of heat input,coarsening of martensitic laths,prior austenite grains,and complete dissolution of M_(23)C_6 precipitates are achieved.Impact toughness of SZ at-20?C is slightly lower than that of base material(BM),and exhibits a decreasing trend with the increase of rotational speed.     

Microstructural analysis of friction stir welded ferritic stainless steel

High-quality, defect-free welds were successfully produced in 409 ferritic stainless steel by friction stir welding. A remarkably fine-grained microstructure was observed in the stir zone, and the fraction of low angle grain boundary in the stir zone significantly increased as compared to that in the base material. An increase in plunging depth led to an increase of the fraction of low angle grain boundary, a decrease in grain size, and an increase in hardness in the stir zone.     

2060搅拌摩擦焊对接接头显微组织与析出相分析

本文选用Al-Li-Cu-Mg系铝锂合金2060,开展搅拌摩擦焊对接接头显微组织与析出相演变规律研究.搅拌摩擦焊对接接头,呈现典型的母材、热影响区、热机影响区和焊核区四区分布特点.母材为双向板条组织,在α板条中有大量三角形AlCu2Mn化合物析出,但在其它相区,当受到热影响时,该相消失;热影响区组织粗大,热机影响区晶粒受到机械力作用,前进侧拉长,后退侧破碎;焊核区为等轴晶组织,出现了高温析出相AlxCuxMn,均布于整个焊核区域.接头显微硬度在母材区最高,热影响区最低,焊核区低于母材,稳定在115 HV.     

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 shoul-der/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 adjustable probes.Therefore,a stable plug failure can be obtained and the joint properties can be improved.     

铝/钢异种金属的超声振动强化搅拌摩擦焊接工艺

采用新型超声振动强化搅拌摩擦焊接工艺实现了6061-T6铝合金以及QP980高强钢的搭接焊,对比分析了有无超声作用下,接头的宏观形貌、微观组织和拉伸剪切性能,同时研究了超声振动对焊接载荷的影响。结果表明:焊接前对母材施加超声振动,可以起到软化母材的作用,促进了材料的塑性流动,扩大了铝/钢界面区和焊核区,使更多的钢颗粒随搅拌针旋转进入铝合金侧,在界面区边缘形成钩状结构,进而提高了接头的失效载荷;超声改变了FSW接头断裂位置和断口形貌,提高了接头力学性能,在本实验工艺参数范围内,接头最大的平均失效载荷为4.99 kN;当焊接速度为90 mm/min,下压量为0.1 mm时,施加超声振动使接头的平均失效载荷提高了0.98 kN,拉剪性能提升28.24%;施加超声振动后轴向力F_z、搅拌头扭矩M_t和主轴输出功率分别下降2.46%,6.44%和4.59%。     

Influence of probe offset distance on interfacial microstructure and mechanical properties of friction stir butt welded joint of Ti6Al4V and A6061 dissimilar alloys

Friction stir butt welding of titanium alloy Ti6Al4V and aluminum alloy A6061-T6 with 2 mm thickness was conducted by offsetting probe edge into the titanium alloy at rotation speed of 750 rpm and 1000 rpm and welding speed of 120 mm/min. The effect of probe offset distance on the interfacial microstructure and mechanical properties of the butt joint was investigated. When the probe offset distance is not sufficient, the two alloys cannot be completely joined together, i.e. there exists no bonding or kissing bonding at the root part of joint interface. However, when the probe offset distance is too large, a great amount of intermetallic compounds are formed at the joint interface and its adjacency, leading to fracturing roughly along the joint interface during a tensile test. In a proper range of probe offset distance, sound dissimilar butt joints are produced, which have comparatively high tensile strength and fracture in heat affected zone of the aluminum alloy during a tensile test.     

Effect of backplate diffusivity on microstructure and mechanical properties of friction stir welded joints

Series of welds were made by friction stir welding (FSW) with various backplates made out of materials ranging from low diffusivity granite to high diffusivity copper in order to reveal the effect of backplate diffusivity on the joint microstructure and properties. The temperature, microstructure, microhardness and tensile properties of joints were compared and discussed. Results show that the backplate with high diffusivity effectively decreases the heat input to the workpiece during FSW. With decreasing the backplate diffusivity the sizes of equiaxed recrystallized grains in the nugget zone increase obviously, while the hardness of the nugget zone also increases a little. The interface between the thermo-mechanically affected zone and nugget zone at the retreating side disappears under the granite backplate. Moreover, the ductility of the joint is more excellent under the copper backplate, but under the granite backplate the failure has mixed fracture characteristics of quasi-cleavage and dimples.     

Analysis of process parameters effects on friction stir welding of dissimilar aluminum alloy to advanced high strength steel

Thin sheets of aluminum alloy 6061-T6 and one type of Advanced high strength steel, transformation induced plasticity (TRIP) steel have been successfully butt joined using friction stir welding (FSW) technique. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Intermetallic compound (IMC) layer of FeAl or Fe₃Al with thickness of less than 1 μm was formed at the Al–Fe interface in the advancing side, which can actually contribute to the joint strength. Tensile tests and scanning electron microscopy (SEM) results indicate that the weld nugget can be considered as aluminum matrix composite, which is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetallic layer or simply intermetallic particles. Effects of process parameters on the joint microstructure evolution were analyzed based on mechanical welding force and temperature that have been measured during the welding process.     

2024铝合金搅拌摩擦焊接头塑性变形行为研究

为了研究搅拌摩擦焊卷焊管坯的力学性能及接头塑性变形行为,以5 mm厚的2024退火态铝合金搅拌摩擦焊板坯为对象,采用网格法测试接头塑性变形分布,用EBSD测量接头各区域晶粒尺寸及位相,并结合SEM观察接头第二相的分布,研究了接头力学性能、应变分布与微观组织之间的关系.研究表明:搅拌摩擦接头强度与母材等强,延伸率下降44%;接头前进侧距离焊缝中心8～17 mm的母材较早出现了应变的集中,局部应变可达23%,而焊核区和接头返回侧母材发生的变形较小,平均应变分别为3%和11%,各区域应变的不均匀主要是由于接头各区晶粒尺寸及位相的差异造成的,导致接头整体延伸率的下降.     

Fracture analysis of dissimilar Al‐Al friction stir welded joints under tensile/shear loading

In this research, fracture of dissimilar friction stir welded (FSWed) joint made of Al 7075‐T6 and Al 6061‐T6 aluminum alloys is investigated in the cracked semi‐circular bend (CSCB) specimen under mixed mode I/II loading. Due to the elastic‐plastic behavior of the welded material and the existence of significant plastic deformations around the crack tip at the propagation instance, fracture prediction of the FSWed specimens needs some failure criteria in the context of the elastic‐plastic fracture mechanics which are very complicated and time‐consuming. For this purpose, the Equivalent Material Concept (EMC) is used herein by which the tensile behavior of the welded material is equated with that of a virtual brittle material. By combining EMC with the 2 brittle fracture criteria, namely the maximum tangential stress (MTS) and mean stress (MS) criteria, the load‐carrying capacity (LCC) of the FSWed CSCB specimens is predicted. Comparison of the experimental results and theoretical predictions from the 2 criteria showed that both criteria could accurately predict the LCC of the cracked specimens. Moreover, as the contribution of mode II loading increases, the size of the plastic region around the crack tip at failure increases, leading to increasing the LCC.     

Properties and microstructure of double-sided friction stir-welded microalloyed steel

This study investigated the properties and microstructures of EH46 microalloyed steel following double-sided friction stir welding. The partially welded material was reversed, completing the weld. Yield strength, elongation and toughness of the weld were similar to those of the base material. During welding, the ferrite-pearlite in the base material transformed to mainly upper bainite, but the overlap or interference zone in the centre of the weld consisted predominantly of 0.5–3?µm recrystallised ferrite grains. The microhardness increased from 240?HV in the base material to 350?HV in bainite but decreased 200–240?HV in the overlap zone. These substantially differing microstructures suggest that the overlap or interference zone was processed at a lower temperature than the remainder of the weld, probably in ferrite.     

Influence of a non-rotating shoulder on heat generation,microstructure and mechanical properties of dissimilar AA2024/AA7050 FSW joints

Friction stir welding (FSW) and stationary shoulder friction stir welding (SSFSW) were carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with thicknesses of 2 mm. A comparison between the two processes was performed by varying the welding speed while keeping the rotational speed constant. Through the analysis of the force and torque produced during welding and a simple analytical model, it was possible to show that in SSFSW there is more effective coupling with the tool and the heat produced is more efficiently distributed. This process decreases both the welding area and the diffusion at the interface of the two alloys compared with FSW. The minimum microhardness occurred at the advancing side (AS) at the interface between the thermo-mechanically affected zone (TMAZ) and the stir zone (SZ) in both processes, although the decrease was more gradual in SSFSW. This interface is also where all specimens failed for both welding technologies. An increase in tensile strength was measured in SSFSW compared with standard FSW. Furthermore, it was possible to establish the mechanical performance of the material in the fracture zone using digital image correlation.     

Effect of self-support friction stir welding on microstructure and microhardness of 6082-T6 aluminum alloy joint

In this paper, 5-mm-thick 6082-T6 aluminum alloy was joined by means of self-support friction stir welding (SSFSW). Here we report the grain structure and second phase particles in various regions including the welding nugget zone (WNZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ). In the upper part of the joint, microhardness in the TMAZ in proximity of the UWNZ was the highest (average 89.4 HV) due to the severe plastic deformation. The similar result was also found in the lower part of the SSFSW joint. The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Some coarse equiaxed grains which were produced in incomplete dynamic recrystallization process and dissolution of some precipitates have been observed in TMAZ. The HAZ retained the same grain structure as the base material, however, the grain size decreased with increasing distance of the weld centerline.     

Effect of position and force tool control in friction stir welding of dissimilar aluminum-steel lap joints for automotive applications

Widespread use of aluminum alloys for the fabrication of car body parts is conditional to the use of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Friction stir welding (FSW) is considered to be a reasonable solution to obtain sound aluminum-steel joints. In this context, this work studies the effects of tool position and force control in dissimilar friction stir welding of AA6061 aluminum alloy on DC05 low carbon steel in lap joint configuration, also assessing proper welding parameter settings. Naked eye and scanning electron microscopy (SEM) have been used to detect macroscopic and microscopic defects in joints, as well as to determine the type of intermixture between aluminum and steel. The joint strength of sound joints has been assessed by shear tension test. Results point out that tool force control allows for obtaining joints with better quality and strength in a wider range of process parameters. A process window has been determined for tool force conditions to have joints with adequate strength for automotive purposes.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-019-00290-1.pdf     

Effect of tool pin eccentricity on microstructure and mechanical properties in friction stir welded 7075 aluminum alloy thick plate

Four different tools with the pin eccentricity of 0.1 mm, 0.2 mm, 0.3 mm and 0.4 mm were designed to friction stir weld 10 mm thick AA7075-O plate. The effect of pin eccentricity on microstructure, secondary phase particles transformation and mechanical properties of the joints was investigated. The results show that the nugget area (A_NZ) increases firstly and then decreases with increasing the pin eccentricity. When the pin with 0.2 mm eccentricity is applied, the A_NZ is the largest; meanwhile the grains size is the smallest which is about 3 μm and secondary phase particles are the most dispersive in nugget zone compared with other tools. While the grains are coarsened to 7–11 μm as the eccentricity is more than 0.4 mm, some coarse hardening particles get to cluster in the thermo-mechanically affected zone. The joints produced by the pin with 0.2 mm eccentricity perform the highest tensile strength and elongation, which is attributed to better interfaces, finer grains and more dispersive secondary phase particles.     

Inhomogeneity of microstructure and mechanical properties in the nugget of friction stir welded thick 7075 aluminum alloy joints

In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.     

Small punch and uniaxial creep fracture behaviours of modified SUS304H steel at various temperatures

Commercial austenitic stainless steel SUS304H with small amount of vanadium addition was used in this study. Small punch (SP) creep and uniaxial tensile creep tests were conducted at 650, 700, and 750 °C to measure creep lives and the minimum displacement rates or the minimum creep strain rates. The measured parameters were compared between the two test methods, seeking empirical relationships among the parameters using Larson-Miller Parameter and Monkman-Grant relation. Magnitude of the applied stress (MPa) in the uniaxial tensile creep test was approximately equal to the applied load value (N) in the SP creep test at all test temperatures. It was shown that during the creep deformation of the SP creep specimen, crack initiation and accompanying crack growth occur simultaneously. Competing failure mechanisms of creep deformation and crack growth may affect the SP creep life and consequently determine the proportionality function, α, in the relation between the SP load and the tensile creep rupture stress in creep tests.     

Microstructures and mechanical properties of friction stir welded dissimilar copper/brass joints

In this study, an experimental investigation has been carried out on microstructure and mechanical properties of friction stir welded copper/brass dissimilar joints. Effect of axial tool force to welding quality has been investigated under obtained optimal tool rotation rate and tool traverse speed conditions. The tool for the dissimilar copper/brass friction stir welding manufactured from X155CrMoV12–1 cold work tool steel with material number of 1.2379. The friction stir welding quality was investigated by welding surface inspections, microstructural studies, micro hardness measurements and tensile tests. The experimental studies have shown that constant axial tool force during pre‐heating and during welding process are very important. As a result, by using 2.5–3 kN of axial tool force during pre‐heating and 5.5 kN of axial tool force during welding process, copper/brass dissimilar joints with well appearance and higher mechanical strength can be obtained.