搅拌摩擦焊焊缝横截面塑性材料迁移行为分析

在搅拌摩擦焊过程中,焊缝塑性材料的迁移是保证焊缝的冶金完整性的重要因素.本研究通过采用镶嵌标示材料的方法,焊后观察焊缝横截面上塑性材料的迁移行为.研究结果表明:在焊缝横截面上,探针附近的塑性材料沿带左旋螺纹的探针表面从焊缝上表面螺旋迁移至焊缝底部,从四周向焊缝表面迁移,在厚度方向上形成一个连续迁移的循环路径.塑性变形的区域关于焊缝中心不对称,塑性材料在焊缝中心形成类似于倾斜"花瓶"状的形貌.从焊缝表面至底面,塑性变形区宽度逐渐减小,前进边塑性材料向焊缝表面迁移的距离小于返回边,前进边塑性变形区小于返回边.     

铝合金薄板高转速FSLW焊接界面形成及迁移行为

目的 研究0.8 mm厚2024铝合金薄板在高转速搅拌摩擦搭接（FSLW）时对其焊接界面的影响规律。方法 通过采用铜粉作为标记材料,探究了高转速FSLW接头的微观组织、焊接界面形成及迁移的特征,揭示了高转速FSLW接头中转速对焊接界面迁移的影响规律。结果 焊接界面是由于原始界面上距焊缝中心线约轴肩半径距离的两侧金属因受到的热循环和机械力不足,难以形成原子间的结合,之后伴随塑性金属的流动,原始界面上距焊缝中心线约轴肩半径距离的两侧金属流向焊缝当中,进而形成未熔合界面。焊接界面的迁移是由于焊缝塑性金属发生了摩擦和挤压,进而引起了焊接界面的向上或向下迁移。结论 铝合金薄板高转速FSLW时,焊接界面在前进侧向上迁移,在后退侧向下迁移。随着转速增加,焊接界面迁移的垂直距离（沿板厚方向）逐渐减小。     

铝合金薄板搭接高速 FSW 缺陷及断裂行为

目的 为了拓展搅拌摩擦焊技术应用,对薄板搭接结构高速搅拌摩擦焊工艺优化与工程应用提供 借鉴与指导。方法 采用圆锥无螺纹搅拌针,进行了 6061 铝合金薄板搭接高速搅拌摩擦焊接,对接头界 面缺陷及其断裂模式进行分析,探讨了转速对 6061 铝合金薄板搭接接头成形及性能的影响规律。结果 发现在无螺纹圆锥搅拌针、高转速（6000~9000 r/min）条件下,接头塑性金属在后退侧易形成飞边流出, 导致下板前进侧出现孔洞缺陷,且随转速增大,界面缺陷尺寸逐渐增大,当转速达到 10 000 r/min 时, 孔洞尺寸有所减小,此时接头拉剪强度最高,为 123 MPa。对试样拉剪断裂位置分析发现,高速搭接接 头断裂位置主要有两种,分别断裂在结合界面处或在前进侧下板,且转速在 9000 r/min 以上越趋向于在 结合界面断裂。结论 高转速搭接焊接必须协调轴肩相貌、焊接工装约束等条件,保证接头塑性金属充 分流动而不流失,才能获得成形良好无缺陷的接头。     

轴肩直径对6061铝合金搅拌摩擦焊轴向力的影响

目的 降低搅拌摩擦焊接过程中的轴向力,选择直径合适的轴肩,提高搅拌摩擦焊的焊接效率以及接头性能。方法 设计并使用了3种不同轴肩直径的搅拌头（9,12,15 mm）对6061铝合金进行焊接,记录并分析焊接轴向力的变化,观察焊缝表面形貌及微观组织,选择合适的轴肩直径。结果 “轴向力-时间”曲线上下起伏,当轴肩直径为15 mm时,曲线呈现较大的起伏;随着轴肩直径的减小,焊接轴向力也随之减小,当焊接速度为95 mm/min,搅拌头旋转速度为1500 r/min时,轴肩直径为9 mm的搅拌头所产生的平均轴向力最小,最小值约为2311 N;9 mm轴肩焊接所形成的焊缝表面形貌光滑,飞边量少;轴肩直径越小,焊核区晶粒尺寸越细小,当轴肩直径为9 mm时,焊核区晶粒尺寸为9.77 μm。结论 在相同的焊接参数下,选用9 mm轴肩所产生的轴向力小,焊缝表面形貌优,焊核区晶粒尺寸细化,接头力学性能好。     

搅拌摩擦焊焊缝塑性流动规律的数值模拟

使用FLUENT流体工程仿真软件对搅拌摩擦焊缝金属的塑性流动进行了数值模拟;初步得出了搅拌摩擦焊焊缝塑性流体流动规律.实验结果表明:随着距轴肩和搅拌针距离的增大,速度场开始减弱,焊缝金属由顶面向底面、由搅拌区向旋转区的流动也随之减弱.     

搅拌摩擦钎焊及其在异种金属搭接焊与复合板制备中的应用

目的克服搅拌摩擦搭接焊(FSLW)焊道狭窄、界面钩型缺陷、匙孔及工具磨损的问题。方法开发了采用无针工具并预置钎料的搅拌摩擦钎焊(FSB)新工艺。综述了FSB要点、优点及主要应用场合。结果FSB利用母材向钎料中的快速溶解替代塑性变形,降低了通过塑性流动实现上下界面混合的苛求。FSB综合了FSW方法的机械去膜、钎焊方法的焊接面积宽大的优点,尤其是可利用双重机制——钎料的冶金作用(共晶反应)及旋转轴肩的力学作用实现界面去膜,并大幅拓宽单道焊合宽度至轴肩直径,故可在大气环境下利用摩擦实现宽幅高效焊接。结论 FSB可用于在大气环境下,实现Al/X与Cu/X异种金属大面积搭接焊、选区复合(比爆炸复合的优点)、复合板与复合管制备等。     

薄板铝铜搭接搅拌摩擦焊工艺

目的研究铝铜异种材料的搅拌摩擦焊搭接工艺,揭示搭接接头界面行为演变的基本规律。方法对1mm的6061铝合金与1 mm的紫铜薄板进行搅拌摩擦焊搭接焊接,测试焊缝的力学性能,对焊缝组织进行分析。结果焊缝表面成形良好,焊缝内部无缺陷。接头的最高拉伸强度达到1447 N,观察拉伸接头断口形貌,发现断裂均发生在上层铝合金的热影响区。结论接头连接界面区域生成钩状"自锁紧"结构,这种钩状"自锁紧"结构增加了铝铜之间的有效接触面积,有利于提高焊缝连接强度。     

双轴肩搅拌摩擦焊接头温度场和流场数值模拟分析

目的 研究铝合金双轴肩搅拌摩擦焊接头温度场和流场规律。方法 以2024铝合金为研究对象,借助FLUENT软件,综合考虑了温度和应变速率对铝合金粘度的影响,采用修正的本构模型,分析了典型双轴肩搅拌摩擦焊接条件下接头温度和速度特征。结果 搅拌头边缘,应变速率较大,接近1000 s-1;温度场呈现出对称的哑铃状分布,最高温度为751 K,达到2024铝合金熔点的83%;前进侧温度大于后退侧温度,前进侧温度为640 K左右,后退侧为600 K左右;双轴肩摩擦焊材料流动速度大于常规焊,前进侧速度大于后退侧速度,前进侧轴肩作用区域大于后退侧;前进侧轴肩作用区域延伸至板材中间,造成带状不连续缺陷。结论 CFD软件Fluent可以较为准确地分析双轴肩搅拌摩擦焊的温度场和流场,可为搅拌工具的优化提供依据。     

纯铝板搅拌摩擦焊温度场数值模拟

建立了搅拌摩擦焊热源模型,利用有限元分析软件ABAQUS模拟了搅拌摩擦焊的温度场,研究了焊接速度、搅拌头轴肩尺寸和垫板材质对搅拌摩擦焊接过程中试板的温度场的影响。结果表明：随着焊接速度的提高,焊件上各点的峰值温度降低,经历高温区的时间减少;轴肩摩擦热是热输入的主要来源,随着搅拌头轴肩尺寸的增加,焊缝中心高温区同一等温线上宽下窄的分布特征越来越明显;垫板材质明显影响焊件底部的温度和分布;适当的焊接参数、搅拌头尺寸及散热条件对获得较好的焊缝质量极为重要。     

搅拌摩擦焊接全过程热力耦合有限元模型

利用ALE网格自适应技术及相应边界条件处理,建立搅拌摩擦焊接全过程(下压阶段和稳定焊接阶段)热力耦合有限元模型。采用6061铝合金焊件验证模型。结果表明:整个焊接过程温度场最高温度在463℃左右,低于材料熔点;稳定焊接6s后,焊件后方横截面上等效塑性应变区近似呈"V"形分布,前进边侧变形程度较返回边侧剧烈,变形范围更大。     

Effect of tool geometry and process condition on static strength of a magnesium friction stir lap linear weld

Friction stir lap linear welding is conducted on overlapped AZ31 magnesium plates with different welding tools. Welds are made mainly with the orientation such that the weld retreating side on the upper plate is to be placed under load. Welding tools consist of a concave shoulder and a pin having a cylindrical, or triangular, or pie shape. This work addresses the effects of tool geometry and process condition on lap shear strength of welds. The shape of the hook formed due to upward bending of the plate interface on the retreating side and the strength of friction stir processed material are quantitatively characterized. Compared to the cylindrical tool, the triangular tool effectively suppresses the hook on the retreating side due to enhanced horizontal material flow. This primarily leads to a 78% increase in optimized weld strength. A ‘pure’ shear surface present on the tool pin significantly reduces weld strength.     

Experimental and numerical investigations of bonding interface behavior in stationary shoulder friction stir lap welding

Stationary shoulder friction stir lap welding (SSFSLW) was employed to weld 2024 aluminum alloy. A coupled Eulerian-Lagrangian (CEL) model was developed to investigate the lap interface behavior during SSFSLW. Numerical results of material movement and equivalent plastic strain were in good agreement with the experimental work. With increasing welding speed, the distances from the hook tip to the top surface of the upper workpiece on the retreating side (RS) and the advancing side (AS) increase, while the distance between two wave-shaped alclads decreases. A symmetric interface bending is observed on the AS and the RS during plunging, while the interface bending on the AS is bigger than that on the RS during welding. The peak temperature of the interface on the AS is higher than that on the RS. The equivalent plastic strain gradually increases as the distance to the weld center decreases, and its peak value is obtained near the bottom of the weld.     

Influence of magnesium AZ80 friction stir weld texture on tensile strain localisation

Synchrotron diffraction was used to construct the first 2D texture maps of entire magnesium AZ80 friction stir welds and showed that basal slip is favoured along most of the advancing side interface, and to a lesser extent on the retreating side interface. Zones of grains optimally oriented for basal slip are known to be a major contributor to strain localisation leading to failure during transverse tensile tests. Profilometry results confirm that the basal plane orientation dominates strain localisation. Microtexture maps traversing the weld interfaces were used to describe the material flow within the weld using scatter from the ideal shear texture fibre. The current results are highly applicable to modelling the strength and ductility of these joints under transverse loading.     

Effect of friction stir welding parameters on morphology and strength of acrylonitrile butadiene styrene plate welds

The aim of this study is to examine the effect of main friction stir welding (FSW) parameters on the quality of acrylonitrile butadiene styrene (ABS) plate welds. Welds were carried out in a FSW machine, using a tool with a stationary shoulder and no external heating system. The welding parameters studied were the tool rotational speed which varied between 1000 and 1500 (rpm); the traverse speed which varied between 50 and 200 (mm/min), and the axial force ranging from 0.75 to 4 (kN). The major novelty is to study the influence of the parameter axial force on FSW of polymers. Produced welds have always a tensile strength below the base material, reaching the maximum efficiencies of above 60 (%) for welds made with higher rotational speed and axial force. Good quality welds are achieved without using external heating, when the tool rotational speed and axial force are above a certain threshold. Above that threshold the formation of cavities and porosity in the retreating side of the stir zone is avoided and the weld region is very uniform and smooth. For low rotational speed and axial force welds have poor material mixing at the retreating side and voids at the nugget. For this reason the strain at break of these welded plates is low when compared with that of base material.     

Process parameters/material location affecting hooking in friction stir lap welding: Dissimilar aluminum alloys

Influence of spindle and weld speeds, metal location, direction of spindle rotation, and tool pin length on hooking in lap FSW of dissimilar aluminum alloys and the effect of hook on tensile and fatigue weld strength was studied. Optical images of the cross-section of the specimen welded at different process parameters were analyzed. The results indicate that increased spindle speed, reduced weld speed, higher tool pin length, clockwise spindle rotation, and locating the stronger material at the bottom of the joint increased the size of the hooking defect. Higher weld speeds and very high spindle speeds resulted in lower hook size on the advancing side (AS) compared to the retreating side (RS) of the joint. Welding with low weld speed would result in higher advancing side hook size compared to the retreating side. Friction stir weld joints fabricated with anti-clockwise spindle rotation has been found to have extremely low hook both on the AS and the RS of the joint. The tensile and fatigue strengths of the weld joints and plates are degraded by the hook. The fatigue strength of welded alloys could be improved by a double pass weld, the second pass welded immediately adjacent to the first pass.     

Process optimisation and mechanical properties of friction stir lap welds of 7075-T6 stringers on 2024-T3 skin

This paper focuses on the results of process optimisation and mechanical tests that were used to ascertain the feasibility of using friction stir welding (FSW) to join stringers to skin. The effects of process parameters on weld quality of 1.5-mm 7075-T6 stringers lap-joined on 2.3-mm 2024-T3 skins were investigated. Advancing and retreating side locations on the joint configuration were alternated to determine optimal design arrangements. The effects of travel and rotation speeds on weld quality and defect generation were also investigated. Weld quality was assessed by optical microscopy and bending tests. It was found that: (i) the increase of the welding speed or the decrease of the rotational speed resulted in a reduction of the hooking size and top plate thinning but did not eliminated them, (ii) double pass welds by overlapping the advancing sides improved significantly the weld quality by overriding the hooking defect, and (iii) change of the rotational direction for a counter clockwise with a left-threaded probe eliminated the top sheet thinning defect. Subsequently, FSW lap joints were produced using optimum conditions and underwent extensive mechanical testing program. Several assembly configurations including discontinuous and continuous welds as well as single and double pass welds were produced. The results obtained for cyclic fatigue performance of FSW panels are compared with riveted lap joints of identical geometry. S–N curves, bending behaviour, failure locations and defect characterisation are also discussed. It was found that: (i) the tensile strength of FSW joints approached that of the base material but with a significant reduction in the fatigue life, (ii) the probe plunge and removal locations served as the key crack nucleation sites in specimens with discontinuous welds, and (iii) double pass welds with overlapping advancing sides showed outstanding fatigue life and very good tensile properties. The present work provided some valuable insight into both the fabrication and application of FSW on stringer/skin lap joints.     

Effect of weld morphology on mechanical response and failure of friction stir welds in a naturally aged aluminium alloy

Friction stir butt welds in 6063-T4 aluminium alloy were obtained using square and two tapered tool pin profiles. Tensile tests at 0°, 45°, and 90° to the weld line, hardness contours in the weld cross-section, temperatures in the heat affected zones, cross-sectional macrographs, transmission electron micrographs, and X-ray diffraction studies were used to characterize the welds. In transverse weld specimen, tunnel defects appearing at higher weld speeds for tapered pin profiles, were found to result in mechanical instabilities, i.e. sharp drops in load–displacement curves, much before macroscopic necking occured. Further, in comparison to the base metal, a marked reduction in ductility was observed even in transverse specimen with defect free welds. Hardness contours in the weld cross-section suggest that loss in ductility is due to significant softening in heat affected zone on the retreating side. Transmission electron microscopy images demonstrate that while recovery and overaging are responsible for softening in the heat affected zone, grain size refinement from dynamic recrystallization is responsible for strengthening of the weld nugget zone. X-ray diffraction studies in the three weld zones: weld nugget zone, heat affected zone, and the base metal corroborate these findings. A weld zone model, for use in forming simulations on friction stir welded plates of naturally aged aluminium alloys, was proposed based on mechanical characterization tests. The model was validated using finite element analysis.     

Defect tolerance of friction stir welds in DH36 steel

Friction stir welding of steel is in the early stages of development. The aim to commercialise this process creates a trade-off between welding time, cost and quality of the joint produced. Therefore, it becomes critical to analyse the lower quality bound of steel friction stir welds in conventional square edge butt welding configuration. Work has been undertaken to evaluate the microstructure and fatigue performance of 6 mm thick DH36 steel plates friction stir welded with sub-optimal process conditions, resulting in the development of embedded and surface breaking flaws. The defective weldments were characterised to understand the nature of the flaws and a programme of mechanical testing was undertaken (including fatigue assessment) to determine the relationship between the flaw geometry, location and weld quality. A number of characteristic flaws were identified and seen to interact with the samples' fatigue fracture mechanisms. Samples with wormholes at the weld root produced the lowest fatigue performance. Fracture from incomplete fusion paths at the retreating side of the welds' top surface was seen to correspond to the highest recorded fatigue lives. The work provides an insight into the complex nature of characteristic flaws in steel friction stir welds and their interaction with fatigue behaviour.     

Effect of weld curvature radius and tool rotation direction on joint microstructure in friction stir welding casting alloys

Curved welds were designed and the effects of the weld curvature radius and tool rotation direction on the microstructure of friction stir welded cast aluminum alloy joints were investigated. Results show that both the weld curvature radius and tool rotation direction have a significant influence on the microstructure of the curved joints during FSW. With decreasing weld curvature radius, the size of the tunnel defect is reduces and the proportion of fine Si particles in the stir zone increases. Si particles are finer and denser in the retreating side (RS) than that in the advancing side (AS) when both the welding direction and tool rotation direction are anticlockwise. However, when the welding direction is anticlockwise while the tool rotates clockwise, the proportions of fine Si particles decrease compared to the former situation. Furthermore, the tunnel defect is more likely to be present in the AS in the former situation.