Microstructure and mechanical properties of friction stir lap welded Mg/Al joint assisted by stationary shoulder

Using magnesium alloy as upper sheet, 3 mm-thick AZ31 magnesium alloy and 6061 aluminum alloy were joined using friction stir lap welding assisted by stationary shoulder. The effects of tool rotating speed on cross-sections, microstructure and mechanical properties of Mg/Al lap joints were mainly discussed. Results showed that stationary shoulder contributed to joint formation, by which stir zones (SZ) were characterized by big onion rings after welding. Because of the big forging force exerted by stationary shoulder, the upper region of hook was well bonded. SZ showed much higher hardness because of intermetallic compounds (IMCs). The bonding conditions at the base material (BM)/SZ interface at advancing side and the hook region played important roles on joint lap shear properties. The X-ray diffraction pattern analysis revealed that the main IMCs were Al₃Mg₂ and Al₁₂Mg₁₇.     

Influence of tool pin design on properties of dissimilar copper to aluminum friction stir welding

Dissimilar friction stir welding (FSW) of copper and aluminum was investigated by nine different tool designs, while the rest of the process parameters were kept constant. Mechanical and metallurgical tests such as macrostructure, microstructure, tensile test, hardness, scanning electron microscope and electron X-ray spectrographs were performed to assess the properties of dissimilar joints. The results exhibited that, the maximum joint strength was achieved by the tool of cylindrical pin profile having 8 mm pin diameter. Besides, the fragmental defects increased as the number of polygonal edges decreased, hence the polygonal pin profiles were unsuitable for dissimilar FSW butt joints. Furthermore, the tensile strength increased as the number of polygonal edges increased. Stir zone of polygonal pin profiles was hard and brittle relative to cylindrical tool pin profiles for same shoulder surface. Maximum hardness of HV 283 was obtained at weld made by the polygonal square pin profile. The hard and brittle intermetallic compounds (IMCs) were prominently presented in the stir zone. Phases of IMCs such as CuAl, CuAl₂, Cu₃Al and Cu₉Al₄ were presented in the stir zone of dissimilar Cu–Al joints.     

Microstructure and Mechanical Properties of Dissimilar Double-Side Friction Stir Welds Between Medium-Thick 6061-T6 Aluminum and Pure Copper Plates

It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding. Thus, double-side friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates, and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed. It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min, while a nonuniform relatively thick intermetallic compound (IMC) layer is formed at the Al/Cu interface, resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass, and seriously deteriorates the mechanical properties of the joint. With the increase of welding speed to more than 300 mm/min void defects appear in the joint, but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface. The maximum tensile strength and elongation of Al/Cu weld are, respectively, 135.11 MPa and 6.06%, which is achieved at the welding speed of 400 mm/min. In addition, due to the influence of welding distortion of the first-pass weld, the second-pass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides. The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.     

静轴肩辅助铝镁搅拌摩擦搭接接头的组织与性能

文中将静止轴肩技术应用到铝镁异种合金的搅拌摩擦搭接过程中,并分析了焊接速度对接头成形和力学性能的影响.结果表明,静止轴肩能够增强上下板之间的材料交换,焊后搅拌区呈较大的洋葱环形貌,其内部分布大量的金属间化合物;搭接面处发生良好的冶金结合.由于生成金属间化合物,洋葱环区域的显微硬度值明显高于接头其它区域.X射线衍射结果表明,金属间化合物的主要成分是Al₃Mg₂和Al₁₂Mg₁₇.接头的抗拉强度随着焊接速度的增加呈先上升后下降的趋势,最大值在焊接速度为40 mm/min时取得.     

温度峰值影响6061铝/AZ31B镁异种材料FSW接头成形的规律

以6061-T6铝合金与AZ31B镁合金为研究对象,基于Abaqus软件进行了异种材料搅拌摩擦焊过程的温度场数值模拟,重点分析搅拌针偏置镁侧下的搅拌区温度峰值影响焊缝表面成形的规律。结果表明,当焊接温度峰值高于Al-Mg共晶温度时,搅拌针根部附近区域会出现较明显的黏着现象,其随着焊接速度的降低而加剧,这与焊接温度峰值的升高相关。随着焊接速度的增加,焊缝表面更易避免裂纹缺陷的产生。当搅拌头的转速为1200r/min且焊接速度为40mm/min时,6061铝/AZ31B镁异种材料焊接接头的表面成形良好。     

Interface morphology and microstructure of high-power ultrasonic spot welded Mg/Al dissimilar joint

High-power ultrasonic welding technology, which has the excellent characteristics of low-energy input and high efficiency, can effectively shorten the welding time, reduce the formation of intermetallic compounds (IMCs), and improve the strength of Mg/Al dissimilar welded joints in the future manufacturing industry. Mg/Al dissimilar metal ultrasonic welded joints with favourable mechanical properties were obtained through reasonable selection of sonotrode patterns and optimisation of welding parameters. The connection mechanisms of joints were discussed based on the analysis of weld interface morphology, microstructure evolution, and the composition and distribution of Mg–Al IMCs that varied with welding energy. The mechanical interlocking phenomenon and discontinuously distributed Mg₁₇Al₁₂ with low thickness were observed at the weld interface, which helped to improve the joint performance.     

带状组织对铝/镁异种金属搅拌摩擦焊接头力学性能的影响

采用搅拌摩擦焊(FSW)对厚度为4 mm的6061铝合金与AZ31B镁合金进行不同工艺的平板对接试验. 采用光学显微镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)及能谱仪(EDS)对接头进行微观组织观察，采用电子万能试验机对接头力学性能进行测试. 结果表明，在接头焊核区(WNZ)中存在着明显的带状组织，带状组织是由插入镁基体中的铝合金条以及弥散分布在条带上的金属间化合物(IMCs)组成；IMCs主要为Al₁₂Mg₁₇和Al₃Mg₂；铝/镁异种金属FSW接头裂纹形核和扩展均发生在带状组织内；焊接工艺影响带状组织形态和IMCs尺寸及数量；随着转速(n)的增加或焊接速度(v)的降低，带状组织呈弯曲状，长度相对较短且呈不连续分布；当转速(n)过高或焊接速度(v)过低时，带状组织变细，但IMCs数量增多且尺寸变大；铝/镁异种金属FSW接头强度主要取决于带状组织形态和IMCs尺寸及数量.     

热压焊接制备的Cu / Al双金属的界面组织和剪切强度

采用扩散焊（DFW）技术制备了Cu/Al双金属，连接温度范围683-803K，连接时间范围20-80min，连接压力15MPa。Cu/Al双金属界面处的SEM试验结果表明，随着焊接温度的升高和保温时间的延长，界面层厚度逐渐增加，在连接温度为803K，连接时间80min，Cu/Al界面处形成了Al4Cu9，Al3Cu4，AlCu、Al2Cu金属间化合物（从铜侧到铝侧），根据扩散动力学，金属间化合物(IMCS)的生成顺序为Al2Cu、Al4Cu9、AlCu、Al3Cu4。Cu / Al双金属的剪切试验显示为脆性断裂，并且界面强度随着IMC的减少而增加。在723 K的焊接温度下进行20分钟焊接后，Cu / Al双金属的剪切强度最高为63.8 MPa。     

冷金属过渡搭接焊镁铝异种金属接头组织及性能

采用冷金属过渡（CMT）焊接工艺,以HS201铜焊丝作为焊缝填充金属对AZ3l镁合金和6061铝合金进行搭接焊接．测试了接头的抗剪强度和显微硬度,并利用光学显微镜（OM）、扫描电镜（SEM）、能谱（EDS）对接头的组织成分及断口形貌进行了分析．结果表明,当焊接电流为109A,电弧电压10．9V,送丝速度4．9mm／s,...     

A Novel Friction Stir Spot Riveting of Al/Cu Dissimilar Materials

In order to eliminate the disadvantages of the keyhole in conventional friction stir spot welding joint and attain the high-strength lap joint of Al/Cu dissimilar metals,a novel welding technique,named as friction stir spot riveting(FSSR),was proposed.A pinless tool and an extra filling stud were employed.The Al/Cu spot joints without keyhole defect were achieved by the FSSR.A Cu anchor-like structure was formed,which greatly increased the mechanical interlocking between the upper Al sheet and lower Cu sheet.The thin intermetallic compounds containing CuAl2 and CuAl at the Al/Cu interface strength-ened the joining interface between the Al sheet and the Cu stud.Increasing rotating velocity increased frictional heat and plastic deformation and then eliminated the interfacial joining defects.The FSSR joint with the maximum tensile shear load of 3.50 kN was achieved at a rotating velocity of 1800 rpm and a dwell time of 20 s,whose fracture path passed through the softened region of upper Al sheet.In summary,the novel FSSR technique has the advantages of strong mechanical interlock-ing and metallurgical bonding between dissimilar materials,thereby attaining the high-strength spot joint.     

铝/黄铜异种金属TIG填丝熔钎焊工艺

采用TIG熔钎焊进行5052铝合金和H62黄铜搭接,选用Al-12% Si药芯焊丝作为填充材料,并对接头微观组织和力学性能进行分析.结果表明,Al-12% Si药芯焊丝在黄铜母材表面润湿性较差,较难获得优质的熔钎焊接头.焊缝中黄铜侧界面层附近过渡区内铝含量较高,与部分熔化和溶解的黄铜母材形成了尺寸较大的条状AlCu金属间化合物相,严重影响接头力学性能.黄铜母材侧界面层由两层不同的金属间化合物相组成,从焊缝到黄铜母材分别为Cu₉Al₄和CuZn.拉伸试验中,试样断裂于黄铜侧过渡区或界面层,断口呈现解理断裂的特征.     

5A06/T2异种材料搅拌摩擦焊接头的耐蚀性

为了研究Al/Cu异种材料搅拌摩擦焊焊缝的耐腐蚀性能,对4mm的5A06和T2搅拌摩擦焊焊接接头进行了浸泡腐蚀试验。结果表明,焊缝区的耐腐蚀性能比铝合金母材要差,而焊缝铝铜结合过渡区耐腐蚀性能最差,并在该区域产生了腐蚀沟。电子能谱和X射线衍射物相分析结果发现,在过渡区Mg含量比其它区域高,而且有少量Al4Cu9产生,它的自腐蚀电位比铝高,这是导致该区域严重腐蚀的主要原因。     

铝/铜异种金属熔钎焊工艺及界面调控方式的研究现状

铝/铜复合结构件具有质量轻、综合性能优异等优势使其在电气电工、航空航天、新能源汽车等行业具有广泛的应用前景。但由于铝/铜在物理化学性能上的差异,使其在焊接过程中存在界面调控等诸多问题。为解决这些问题,国内外研究者通过工艺调控和冶金调控来抑制金属间化合物的生长,促进Al/Cu之间的冶金结合。文中从铝/铜熔钎焊方法进行了综述介绍,重点总结了焊接接头界面调控的方法,提出了该领域的研究热点及难点,并且探究了未来铝/铜焊接的发展趋势及应用前景。结果表明,从焊接效率、焊接强度来看当属熔钎焊最佳,但是其接头处的金属间化合物影响了其机械性能,通过添加微量元素的冶金调控,可以使其力学性能大幅提升。     

Residual stress measurement of Al/steel dissimilar friction stir weld

ABSTRACT

The dissimilar welds between aluminium (Al) alloy, A6061-T6, and stainless steel, type 304, were fabricated by a friction stir welding (FSW) technique. The FSW tool was offset to Al side and the probe was inserted only into Al plate. The softening occurred in Al side due to the heat input during FSW, while the hardness increased by the post-ageing treatment. Tensile strength of dissimilar weld also increased about 8.5% by the post-ageing. The residual stresses were measured based on the cos α method. The residual stresses parallel to the weld line, σ_xr, were predominantly tensile, while those perpendicular to the weld line, σ_yr, were compressive. Post-ageing treatment had little effect on the residual stresses.     

外加热源对铝-铜搅拌摩擦焊对接的影响

为了改善铝-铜搅拌摩擦焊对接接头的焊缝接头性能,文中采用对焊缝铜一侧引入外加热源的方法,来增加焊接热输入,提高铜侧材料的软化程度.结果表明,外加热源能够有效提高焊缝部位铜一侧的焊接温度,从而增加焊接过程中铜一侧的塑化流动性,形成成形良好的焊接接头.通过焊缝的物相对比可知,外加热源引起的温度场的改变,有效地减少了焊缝中CuAl,CuAl₂等中间相的含量,增加了铜颗粒在焊缝中的含量.在力学性能上表现为有外加热源的焊缝拉伸强度较高,显微硬度分布均匀.     

Preparation of bimetallic nano-composite by dissimilar friction stir welding of copper to aluminum alloy

Butt friction stir welding between pure copper and AA5754 alloy was carried out. Reinforcing SiC nano- particles were utilized in friction stir welded (FSW) joints to decline the harmful effects of intermetallic compounds. Tensile tests, micro-hardness experiments, scanning electron microscopy and X-ray diffraction analysis were applied to studying the properties of welded joints. The joints with a travel speed of 50 mm/min and a rotation speed of 1000 r/min showed the best results. The presence of nano-sized SiC particles reduced the grain size of aluminum and copper in the stir zone (SZ) from 38.3 and 12.4 μm to 12.9 and 5.1 μm, respectively. The tensile strength of the joint in the presence of reinforcing SiC nano-particles was ~240 MPa, which is ～90% of that for the aluminum base. Furthermore, the highest microhardness of the weld zone was significantly increased from HV 160 to HV 320 upon the addition of SiC nano-particles. The results also showed that raising the heat generation in FSW joints increased the amount of Al₄Cu₉ and Al₂Cu intermetallic compounds.     

纯铝纯铁搅拌摩擦焊接头的组织与力学性能

选用3 mm厚冷轧态高纯铝板和退火态高纯铁板作为焊接母材,使用300/400/500/600 r/min-100 mm/min和300 r/min-80/60 mm/min焊接参数进行铝/铁异种金属搅拌摩擦焊对接焊试验。对焊接接头进行显微硬度和拉伸性能测试,通过扫描电镜(SEM)、能谱仪(EDS)、电子背散射衍射(EBSD)等对接头组织进行表征。焊缝宏观形貌观察发现,焊缝的正面和背面有孔洞,正面出现毛刺。随着转速焊速比增加,孔洞消失毛刺增加。拉伸试验结果显示,共出现3种失效模式,分别为在300 r/min-100 mm/min参数下孔洞缺陷处断裂,300 r/min-80/60 mm/min参数下Al/Fe界面断裂和400/500/600 r/min-100 mm/min处Al侧基体断裂,3种模式下的最大焊接效率分别为40.1%、41.0%和60.4%,其中Al侧基体断裂模式的焊接效率最高。出现在焊核区的孔洞降低了接头强度,导致了缺陷断裂;在300 r/min低转速下,界面未达到有效的冶金结合,界面强度低于Al基体强度,导致Al/Fe界面断裂。硬度试验结果显示,铝侧硬度呈现先下降后上升...     

Enhancing metallurgical and mechanical properties of friction stir lap welding of Al–Cu using intermediate layer

Abstract

In this paper, the material behaviour and mechanical characteristics of lap joint friction stir welding (FSW) between dissimilar alloys, namely, Cu and Al, is investigated. In order to produce welds of a higher quality, a layer of Cu is anodised on the aluminium alloy. The mechanical and the microstructural characterisations are performed on the welds, which are produced using various welding parameters. Scanning electron microscope with energy dispersive X-ray spectroscopy is used to identify the elemental compositions of phases that are formed. The results reveal that the use of the copper anodised layer prevented formation of brittle intermetallic compounds due to the direct FSW of 6061 aluminium alloy to copper and, as a result, enhanced the weld metallurgical and mechanical properties.     

TC4钛合金与Al6061铝合金热等静压扩散连接接头的界面特征及力学性能

对TC4钛合金和Al6061铝合金的异种金属进行了热等静压扩散连接实验,研究了TC4/Al6061连接接头的界面特征、形成机制和力学性能,并通过热力学分析解释相关实验现象。结果表明,热等静压扩散连接及后续退火处理后,两侧母材元素发生了明显的互扩散,其中Si、Mg元素在化学势驱动力作用下分别富集于扩散过渡区和Al侧界面。接头界面发生冶金反应生成TiAl₃、TiAl、Ti₃Al等金属间化合物,通过有效生成热模型计算表明TiAl₃相优先生成。硬度实验表明界面生成的Ti-Al金属间化合物具有较高的硬度。拉伸实验显示接头最大抗拉伸强度达到了144 MPa。     

转速对6061铝合金/纯铜异种金属搅拌摩擦焊接头组织与性能的影响

采用搅拌摩擦焊技术对4 mm厚6061-T6铝合金和纯铜进行连接,研究转速对铝铜异种金属接头组织与力学性能的影响。结果表明,当焊接速度为30 mm/min、搅拌头转速在1 200~1 800 r/min的范围内,可以获得表面成形良好、无缺陷的铝铜异种金属接头。大量破碎的铜被搅入焊核区,形成了组织结构复杂的区域。通过EDS和XRD分析,在焊核区内发现了Al_2Cu、Al_4Cu_9和Al Cu金属间化合物。在界面处,铝和铜发生相互扩散形成金属间化合物层,随着转速的提高,化合物层逐渐变厚。由于晶粒细化、固溶强化作用以及金属间化合物的生成,异种接头的焊核区平均显微硬度值高于铝铜两侧平均硬度,并且在焊核区出现硬度峰值点。随着转速的增加,接头抗拉强度呈现先增大后减小的趋势,所得最优接头抗拉强度为183 MPa,达到铜母材的71.8%,断裂位置位于铝侧热影响区,断裂方式为韧性断裂。