异种铝合金摩擦塞补焊工艺与组织性能

采用顶锻式摩擦塞补焊方法,以2219-T6铝合金为塞棒材料,分别对8 mm厚2024-T3和7075-T6两种铝合金FSW接头进行了摩擦塞补焊试验研究,深入探讨了不同焊接压力下塞补焊接头的微观组织、显微硬度、力学性能及断口形貌特征. 结果表明,塞棒和母材或FSW焊缝是由等轴晶进行过渡,获得了紧密结合的接头,热力影响区和热影响区晶粒发生长大. 整个塞补焊接头塞棒区软化最严重,硬度在85 ~ 95 HV之间. 2024铝合金塞补焊接头抗拉强度和断后伸长率分别达到了母材的70%和65%以上,7075铝合金塞补焊接头抗拉强度和断后伸长率分别达到了母材的62%和48%以上. 塞补焊接头断裂模式为韧性特征.     

Establishing empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints

AA 6061-T6 aluminium alloy(Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high specific strength and good corrosion resistance.Compared with the fusion welding processes that are routinely used for joining structural aluminium alloys,friction stir welding(FSW) process is an emerging solid state joining process in which the material welded does not melt and recast.Joint strength is influenced by the grain size and tensile strength of the weld nugget region.Hence,an attempt was made to develop empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints.The empirical relationships are developed by response surface methodology(RSM) incorporating FSW tool and process parameters.A linear regression relationship was also established between grain size and tensile strength of the weld nugget of FSW joints.     

Experimental study on temperature distributions within the workpiece during friction stir welding of aluminum alloys

This study aims to experimentally explore the thermal histories and temperature distributions in a workpiece during a friction stir welding (FSW) process involving the butt joining of aluminum 6061-T6. Different types of thermocouple layout are devised to measure the temperature histories during FSW at different locations on the workpiece in the welding direction. Successful welding processes are achieved by appropriately controlling the maximum temperatures during the welding process. Regression analyses by the least squares method are used to predict the temperatures at the joint line. A second-order polynomial curve is found to best fit the experimental temperature values in the width direction of the workpiece. The Vickers hardness test is conducted on the welds to evaluate the hardness distribution in the thermal-mechanical affected zone, the heat affected zone, and the base metal zone. Tensile tests are also carried out, and the tensile strength of the welded product is compared with that of the base metal.     

AA6061-T6与AZ31合金异种搅拌摩擦焊接头的微观组织

研究了AA6061-T6和AZ31合金异种搅拌摩擦焊接头的微观组织。在异种搅拌摩擦焊接AA6061-T6与AZ31合金时,采用偏置条件,即将搅拌针插入时偏向AZ31合金,从而得到异种对接接头。通过预备实验来优化搅拌针的前进速度、旋转速度。运用电子背散射衍射技术观察搅拌区的纹理,并得到粒径分布和错位角分布,在搅拌区存在相对精细的晶粒结构。在AA6061-T6搅拌区出现随机或弱面取向,而在AZ31搅拌区出现旋转底面取向。再结晶颗粒的平均尺寸只有2．5～4．5μm。与基础合金相比,在AA6061-T6搅拌区的大角度晶界的分数增大,而在AZ31搅拌区的小角度晶界的分数降低。     

搅拌摩擦焊接的传热和力学计算模型

搅拌摩擦焊接（Ｆｒｉｃｔｉｏｎ Ｓｔｉｒ Ｗｅｌｄｉｎｇ）是最近发展起来的一种新的固态连接技术。它主要用于铝合金,可以得到小变形、低成本和高质量的焊接接头。本文提出一个基于三维热弹塑性有限元分析的传热和力学计算模型。利用该模型可以了解搅拌摩擦焊接过程中的温度分布和循环,并预测焊后的残余应力和变形。对６０６１－Ｔ６铝合金搅拌摩擦焊接进行了实例分析。传热分析表明,铝合金搅拌摩擦焊接时的最高温度不超过材料熔点的８０％,因而属固态连接,同时为预测焊接接头的组织性能提供依据。力学计算结果表明,搅拌摩擦焊接的残余应力与变形要比传统的熔化焊接方法小得多。工件中最大的残余应力大约只有母材屈服极限的２５％～３０％。计算结果与试验数据相近,可作为进一步研究搅拌摩擦焊接过程和优化焊接参数的有效工具。     

Mechanical properties of friction stir welded Al alloys with different hardening mechanisms

The mechanical properties of precipitation hardened Al 6061-T651 and Al 7075-T6 and strain hardened Al 5083-H32, friction stir welded with various welding parameters, were examined in the present study. 4 mm thick Al 6061-T651, Al 7075-T6, and Al 5083-H32 alloy plates were used for friction stir welding (FSW) with rotating speed varied from 1000 to 2500 rpm (rotation per minute) and welding speed ranging from 0.1 to 0.4 mpm (m/min). Each alloy displayed slightly different trends with respect to the effect of different welding parameters on the tensile properties of the FSWed Al alloys. The tensile elongation of FSWed Al 6061-T651 and Al 7075-T6 tended to increase greatly, while the tensile strength decreased marginally, with increasing welding speed and/or decreasing rotating speed. The tensile strength and the tensile elongation of Al 6061-T651 decreased from 135 to 154 MPa and 10.6 to 17.0%, respectively, with increasing welding speed from 0.1 to 0.4 mpm at a rotating speed of 1,600 rpm. Unlike the age-hardened Al 6061-T651 and Al 7075-T6, the strain-hardened Al 5083-H32 showed no notable change in tensile property with varying welding parameters. The change in the strength level with different welding parameters for each alloy was not as significant as the variation in tensile elongation. It was believed that the tensile elongation of FSWed Al alloys with varying welding parameters was mainly determined by the coarse particle clustering. With respect to the change in tensile strength during friction stir welding, it is hypothesized that two competing mechanisms, recovery by friction and heat and strain hardening by plastic flow in the weld zone offset the effects of different welding parameters on the tensile strength level of FSWed Al alloys.     

Effect of Temperature on Microstructure and Fracture Mechanisms in Friction Stir Welded Al6061 Joints

Aluminum and its alloys are widely used in different industries due to such attractive properties as adequate strength, ductility, and low density. It is desirable to characterize welds of aluminum alloys obtained using “friction stir welding” at high temperatures. Al-to-Al (both 6061-T6) butt joints are produced by friction stir welding at tool rotation speed of 1600 rpm and four levels of tool advancing speeds: 250, 500, 750, and 1000 mm/min. Microstructural properties of the different welds are investigated. Observed are noticeable differences in microstructure characteristics between the various weld zones. Mechanical properties of these welded joints are characterized under tensile tests at temperatures of 25, 100, 200, and 300 °C, at a constant strain rate of 10^?3/s. The optimum microstructural and mechanical properties were obtained for the samples FS welded with 1600 rpm tool rotation speed at 1000 mm/min tool advancing speed. The studied welds exhibited yield strength, ultimate tensile strength, and strain to failure with values inferior of those of the base material. Observations of postmortem samples revealed that in the temperature range of 25-200 °C the locus of failure originates at the region between the thermo-mechanically affected zone and the heat-affected zones. However, at higher temperatures (300 °C), the failure occurs in the stir zone. A change in the crack initiation mechanism with temperature is suggested to explain this observation.     

Residual stress engineering in friction stir welds by roller tensioning

Abstract

The authors investigate the efficacy of applying rolling pressure along the weld line in thin butt welds produced using friction stir welding (FSW) as a means of controlling the welding residual stresses. Two cases are examined and in each case, comparison is made against the as welded condition. First, for FSW of AA 2024 aluminium alloy, roller tensioning was applied during welding using two rollers placed behind and either side of the FSW tool. Very little effect was seen for the down forces applied (0, 50, 75 kN). Second, for FSW AA 2199 aluminium alloy, post-weld roller tensioning was applied using a single roller placed directly on the FS weld line. In this case, significant effects were observed with increased loading, causing a marked reduction in the longitudinal tensile residual stress. Indeed, a load of just 20 kN was sufficient to reverse the sign of the weld line residual stress. Only slight differences in Vickers hardness were observed between the different applied loads. Furthermore, unlike some methods, this method is cheap, versatile and easy to apply.     

Rupture locations of friction stir welded joints of AA2017-T351 and AA6061-T6 aluminum alloys

The tensile rupture locations of friction stir welded joints of AA2017-T351 and AA6061-T6 aluminum alloys were examined. The experiments show that the rupture locations of the joints are different for the two aluminum alloys, which are influenced by the welding parameters. When the joints are free of welding defects, the AA2017-T351 joints are ruptured in the weld nugget adjacent to the thermo-mechanically affected zone on the advancing side and the rupture surfaces appear as oval contours of the weld nugget, while the AA6061-T6 joints are ruptured in the heat affected zone on the retreating side and the rupture surfaces are inclined at a certain degree to the bottom surfaces of the joints. When welding defects are present in the joints, the AA2017-T351 joints are ruptured in the weld center, while the AA6061-T6 joints are ruptured on the retreating side near the weld center. The rupture locations of the joints are dependent on the internal structures of the joints and can be explained through them.     

2024-T3铝合金搅拌摩擦焊接中搅拌头尺寸和搅拌针形状影响的数值模拟

采用完全热力耦合模型研究了搅拌针直径、轴肩直径以及搅拌针锥角对2024-T3铝合金搅拌摩擦焊接过程中热生成、材料变形和能量历史的影响。结果表明：相比搅拌针接触面,轴肩接触面对搅拌摩擦焊接的热生成起主要作用。增加轴肩直径和减小搅拌针直径均能增加焊接温度,但是轴肩尺寸变化的影响更为明显。与6061-T6铝合金的搅拌摩擦焊接过程相比,2024-T3铝合金搅拌摩擦焊接的能量输入明显增加,同时塑性耗散与摩擦耗散的能量比减小。     

6061-T6铝合金的静止轴肩搅拌摩擦焊工艺及组织性能

采用自主研制的静止轴肩搅拌摩擦焊工具系统成功获得了6061-T6铝合金的对接接头. 对该接头的焊缝成形、显微组织、硬度分布以及拉伸性能分别进行了试验研究. 结果表明,SSFSW工艺所得6061-T6铝合金接头具有非常美观的焊缝成形,与常规的FSW工艺相比,几乎没有出现焊缝减薄的现象;焊缝组织分区也有明显的不同,TMAZ非常窄,只有几百微米;接头的硬度呈"W"形分布;在转速1 000 r/min,焊速为200 mm/min时,接头的抗拉强度和断后伸长率达到最大,分别为母材的71.5%和44.6%;拉伸试样均断裂在热影响区,它是接头发生断裂的最薄弱区域.     

Microstructure characterization and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy

The microstructure, microhardness and quasi-static failure behavior of resistance spot welds of AA6111-T4 aluminum alloy were experimentally investigated. Optical metallography and high-resolution hardness traverses were utilized to characterize the weld nugget, heat affected zone and base metal. The AA6111 spot welds displayed a softer nugget and hardened heat affected zone, compared with the base metal. The through-thickness hardness of the base metal sheet was not constant and had to be carefully considered to determine the effect of welding on material properties. Quasi-static lap-shear tensile tests were used to determine the failure load and failure mode. All tensile specimens failed through the interfacial fracture. This failure mode is consistent with the observed reduced hardness in the weld nugget.     

Numerical and Experimental Investigations on the Loads Carried by the Tool During Friction Stir Welding

A computational fluid dynamics (CFD) model is presented for simulating the material flow and heat transfer in the friction stir welding (FSW) of 6061-T6 aluminum alloy (AA6061). The goal is to utilize the 3-D, numerical model to analyze the viscous and inertia loads applied to the FSW tool by varying the welding parameters. To extend the FSW process modeling, in this study, the temperature-dependant material properties as well as the stick/slip condition are considered where the material at the proximity of the FSW tool slips on the lower pressure regions. A right-handed one-way thread on a tilted FSW tool pin with a smooth, concaved shoulder is, additionally, considered to increase the accuracy of the numerical model. In addition, the viscous and frictional heating are assumed as the only sources of heat input. In the course of model verification, good agreements are found between the numerical results and the experimental investigations.     

厚板铝合金FSW和MIG焊接接头疲劳性能

对厚度10 mm的6082-T6铝合金搅拌摩擦焊(FSW)和MIG焊接接头的疲劳强度进行了试验研究,并与6082-T6母材疲劳性能进行了对比分析.结果表明,6082-T6母材的疲劳S-N曲线最高、MIG焊接接头S-N曲线度最低,而FSW接头的疲劳S-N曲线近似位于两者之间;在高应力区FSW疲劳强度低于MIG焊接接头、而在低应力区高于MIG焊接接头.大部分FSW试样疲劳裂纹启始于焊缝根部的"弱连接"缺陷,采用机械加工去掉1.4 mm厚度焊缝根部材料后,FSW疲劳强度明显提高并接近母材数据.厚板6082-T6铝合金FSW焊缝根部质量控制是影响疲劳性能的关键因素.     

Experimental defect analysis and force prediction simulation of high weld pitch friction stir welding

Abstract

Experimental data for AA 6061-T6 friction stir welded at rotational and travel speeds ranging from 1000 to 5000 rev min^?1 and from 290 to 1600 mm min^?1 (11–63 ipm) are presented. The present paper examines the forces and torques during friction stir welding (FSW) with respect to mechanistic defect development owing to process parameter variation. Two types of defects are observed: wormholes and weld deformation in the form of significant excess flash material. A 3D numerical model, implemented using the computational fluids dynamics package Fluent, is used to simulate and investigate the parametric relationship of the forces and torques during FSW. In order to establish a mechanistic quantification of the FSW process, two mechanical models, the Couette and the viscoplastic fluid flow models, were simulated and compared with experimental data for AA 6061-T6.     

6061铝合金FSW接头与MIG焊接头对比试验

采用搅拌摩擦焊(FSW)和MIG焊分别对6061铝合金板进行了焊接试验,测试了焊接接头的强度,观察了焊接接头的金相组织,并进行了接头的硬度分布测试.结果表明,搅拌摩擦焊接头抗拉强度高达212.05 MPa,是母材抗拉强度的86％,比MIG焊的接头强度略高.焊接接头软化区宽度比MIG焊接头软化宽度窄.6061铝合金母材为典型的轧制组织,焊核区为细小的等轴晶组织,MIG焊接头焊缝为柱状晶组织.     

Effect of welding heat input and post-weld aging time on microstructure and mechanical properties in dissimilar friction stir welded AA7075–AA5086

The effects of welding heat input and post-weld heat treatment on the mechanical and microstructural aspects of dissimilar friction stir welds of age-hardened AA7075-T6 and strain hardenable AA5086-H32 aluminium alloys were investigated. X-ray diffraction (XRD) residual stress analysis and tensile testing together with optical metallography and transmission electron microscopy (TEM) were performed to assess the effects of process parameters on welded joints. It was discovered that joints produced without heat sink exhibited more homogeneous stir zones than other joints. Of the natural aging time studied, higher amount of solid solution during rapid cooling of welds produced higher driving force for increase in hardness in the AA7075 side during natural aging. Natural aging within stirring zone and thermo-mechanical affected zone of AA7075 side resulted in a 10 to 25 MPa reduction in the residual stress in these zones; its effect decreased considerably in the welds performed without heat sink. In addition, natural aging had no noticeable effect on the joint strength.     

铝合金板材温热成形性能

在20℃～300℃的温度范围内,分别对7B04-T6和6061-T6铝合金薄板进行了单拉试验,结果表明,7B04-T6高强度铝合金的断后延伸率和拉伸极限应变在温热状态下都有显著的提高,比较适合于温热成形,而6061-T6则不太适合。另外,基于Fields&Backofen本构方程,对7B04-T6在不同温度状态下的强化规律进行了分析和探讨,结果表明,随着温度的逐渐升高,应变强化指数n值不断减小,应变率敏感系数m值则显著增大,应变率强化明显增强,这也是在温热状态下其成形性能提高的主要原因。     

Comparative study on fatigue properties of friction stir and MIG-pulse welded joints in 5083 Al-Mg alloy

The objective of this investigation was to compare the fatigue properties of friction stir welds with those of MIG-pulse welds. The 5083 Al-Mg alloy was welded by single pass friction stir welding（FSW） and double-sided MIG-pulse welding. The results show that friction stir（FS） welds have a better appearance than MIG-pulse welds for the lack of voids, cracks and distortions. Compared with the parent plate, FSW welds exhibit similar fine grains, while MIG-pulse welds display a different cast microstructure due to the high heat input and the addition of welding wire. The S-N curves of FSW and MIG-pulse joints show that the fatigue life of FS welds is 18 - 26 times longer than that of MIG-pulse welds under the stress ratio of 0.1 and the calculated fatigue characteristic values of each weld increase from 38.67 MPa for MIG-pulse welds to 53.59 MPa for FSW welds.     

On the growth of intermetallic phases by heat treatment of friction stir welded aluminum steel joints

Multi-material components made from aluminum and steel sheet metal are an innovative approach for weight reduction in automotive applications. However, lightweight components made from aluminum and steel require suitable joining technologies. A promising solid-state welding technology for producing dissimilar steel aluminum joints is Friction Stir Welding, which minimizes the formation of Fe-Al intermetallic phases due to process temperatures lower than the melting temperatures of the base material. The results obtained show a comparison of steel aluminum joints made by FSW using DC04 mild steel with the strain hardened aluminum alloy AA5754-H22 on the one hand and the precipitation hardened aluminum alloy AA6082-T6 on the other hand. The difference between achieved maximum tensile strengths of the joints in relation to those from both base materials is investigated. Due to the stirring and heat input of the welding process, the temper condition of the precipitation hardened aluminum alloy is changed. To improve the mechanical properties of the welded joints, post weld heat treatments are performed. The post weld heat treatments of the produced multi-material specimens from AA6082-T6 aluminum alloy and mild steel at various heat treatment conditions show substantial growth of intermetallic phase layer, which is characterized in detail within the present work. Tensile tests show a degradation of the mechanical properties resulting in a decreased tensile strength and insufficient connection of both materials. Investigations using a scanning electron microscope (SEM) show a distinct increase of the thickness of intermetallic phases in the transition between aluminum and steel.