State of the art about dissimilar metal friction stir welding

Friction stir welding is a rather recent welding process (patented in 1991 by Thomas et al., ‘Improvements to friction welding’ UK patent application no. 9125978.8, US Patent 5460317, 1995) that has shown great potential for welding dissimilar materials even of different metallic nature, e.g. Al to steel, Mg to steel, Al to Ti, Mg to Ti, Al to Cu, Al to Mg. This review presents the specific microstructural features and mechanical properties, in particular tensile strength, of such welds. A focus will be on the material flow and welding defects, on the intermetallic compounds, on constitutional liquation, on particularities related to dissimilar lap welding and finally on process modifications to improve dissimilar friction stir weldability.     

Towards attaining dissimilar lap joint of CuCrZr alloy and 316L stainless steel using friction stir welding

CuCrZr alloy (Cu-0.8wt-%Cr-0.1wt-%Zr) and 316L stainless steel (Fe-0.03wt-%C-16wt-%Cr-10wt-%Ni) plates were successfully friction stir lap welded resulting in significant mechanical mixing of the two matrix elements, Cu and Fe, in the stir zone. The severe mixing not only led to improved load bearing response but also leads to form Cu-rich and Fe-rich regions in the weld nugget. The formation of these phases governs the failure mechanism of the joint. Tensile properties of the weld showed promising response when compared with joints made for the similar alloy pair by other welding techniques. This suggests strong feasibility of applying FSW for joining Cu and steel for nuclear applications.     

基于镍合金中间层的镁/钢异质金属激光-电弧复合胶焊技术

采用激光-TIG电弧复合胶焊技术实现了AZ61镁合金与Q235钢之间的良好连接.重点讨论了激光-TIG复合胶焊的焊缝表面形貌、焊缝区组织及元素分布特征.结果表明,在胶粘剂厚度一定时,焊接热输入是影响焊缝成形的关键因素.胶粘剂在复合热源作用下分解气化并逸出熔池,在一定程度上增强熔池内部液态金属的流动性,促进熔池内部异质金属之间冶金反应和相互混合.通过镍合金层与胶粘剂的综合作用使镁/钢异质材料之间以冶金反应形式连接,提高了镁/钢异质金属连接结构的线载荷,增强了镁/钢异质金属的整体性能.     

机床用铝合金/不锈钢的异质搅拌摩擦焊工艺

采用不同工艺参数下的搅拌摩擦焊对接焊方法,进行了机床用6063铝合金/304L不锈钢的异质焊接试验,并进行了接头的X光无损检测以及显微组织和力学性能测试。结果表明,搅拌头旋转速度500~650 r/min、焊接速度155~185 mm/min时可获得良好的焊接接头;接头抗拉强度可达139 MPa,达到6063铝合金母材抗拉强度的67%,达到304L不锈钢母材抗拉强度的17%。搅拌头旋转速度优选550 r/min、焊接速度优选180 mm/min。     

铝合金与钢的异种材料离焦激光焊研究现状

综述了铝合金与钢的异种材料离焦激光焊技术的研究现状;介绍了基于非定常热传导利用境界要素法对铝合金与钢离焦激光焊接合界面温度分布的解析和接头界面微观组织特性、力学性能与工艺条件的关系.就铝合金与钢离焦激光焊可焊范围与垫砧材质等工艺条件关系进行了探讨,并指出了今后铝合金与钢异种材料激光焊的研究方向.     

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.     

镍箔中间层对不锈钢/铝合金激光深熔焊的影响

以不锈钢201和铝合金5052作为试验材料,添加镍箔作为中间层,配合钢上铝下的搭接接头形式,采用激光深熔焊方法进行了焊接试验,分析了热输入对焊缝成形的影响以及添加镍箔后接头力学性能与不锈钢／铝合金焊接性的变化,并提出了焊缝下凹深宽比r以表征焊缝对应力集中的敏感程度．结果表明,热输入升高会导致焊接过程中飞溅增加,焊缝宽度与下凹程度增大,熔穿深度升高;不锈钢焊缝金属嵌入到铝合金内的熔穿深度对焊缝的力学性能有着重要的影响;镍中间层的添加有效地改善了接头力学性能,扩大了可用的工艺参数范围．     

TiAl合金与异种材料的摩擦焊接

TiAl合金与42CrMo直接摩擦焊接性较差,为此分别引入高温合金GH3039、K418、N80A和纯镍N6作为中间材料,对TiAl-GH3039/K418/N80A/N6-42CrMo异种材料的摩擦焊接工艺进行了研究。采用硬度计、扫描电镜和电子万能试验机对焊后接头区域的硬度、组织和焊合区成分变化以及接头力学性能进行了分析。研究表明,TiAl合金与异种材料焊后接头中形成了复杂的多层状金属间化合物;TiAl合金与GH3039、N80A的摩擦焊接性较好,与K418、N6的摩擦焊接性较差;根据不同材料线膨胀系数随温度的变化规律、与TiAl合金摩擦焊接后接头的性能及其与42CrMo的摩擦焊接性,最终选择GH3039作为中间材料。通过引入中间材料,摩擦焊制备了TiAl合金涡轮-42CrMo转轴的异种材料整体转子,使得TiAl合金在涡轮增压器领域的应用成为可能。     

Thermomechanical deformation behaviour of DH36 steel during friction stir welding by experimental validation and modelling

Friction stir welding is a solid state thermomechanical deformation process from which the plasticisation behaviour of the stirred material can be evaluated through the study of flow stress evolution. Flow stress data also supporting the development of a local microstructural numerical model have been generated. Hot compression testing of DH36 steel has been performed at a temperature range of 700–1100°C and strain rates from 10^?3 to 10² s^?1 to study the alloy’s thermomechanical deformation behaviour in conditions that simulate the actual friction stir welding process. It has been found that the evolution of flow stress is significantly affected by the test temperature and deformation rate. The material’s constitutive equation and constants have been calculated after analysis of these data. Preliminary numerical analysis results are in good agreement with experimental observations.     

Novel dissimilar spot welding of aluminium alloy and steel sheets by friction stirring

Friction stir spot welding (FSSW) has been applied to a dissimilar metal lap joint of an aluminium alloy and steel by stirring only the upper aluminium alloy sheet. Therefore, FSSW cannot be used to weld a lap joint composed of three or more sheets and a lap joint with an adhesive interlayer. In the present work, we propose a novel spot welding process for dissimilar metal lap joints using a new tool with the tip made of spherical ceramics. When this process is applied to the lap joint of the aluminium alloy and steel, the tool can be plunged into the lower steel sheet, then a steel projection is formed in the aluminium alloy sheet. The height of this steel projection increases with the plunge depth, and accordingly, the weld strength increases; the tensile shear strength and the cross tensile strength reached about 3.6 and 2.3 kN/point, respectively.     

铝合金/镀锌钢异种材料薄板的超声波点焊

为了实现铝合金和钢板的高效连接,对3003铝合金和镀锌钢板进行了超声波点焊. 研究了接头的显微组织特征、焊接参数对接头性能的影响以及焊缝区的温度变化过程. 结果表明,超声波焊接可以对3003铝合金与镀锌钢板进行有效连接;镀锌层被不规则挤出,铝合金与钢直接接触区形成了FeAl₃和Fe₂Al₅相;在一定范围内,随着焊接时间的增加,接头抗拉强度先增加后减小,其减小的原因是过长的焊接时间诱导显微组织演变;当焊接时间为240 ms,焊接压力为0.4 MPa时,获得接头的最大抗拉力为673.05 N;在文中试验条件下,焊接区最高温度达到390 ℃.     

Dissimilar spot welding of aluminium alloy and galvannealed steel by metal flow-application of friction anchor welding to aluminium alloy and Zn-coated steel

ABSTRACT

Lap joints of an upper Al alloy (1.0-mm-thick A5052) and lower hot dip galvanized steel (1.2-mm-thick GI steel) were welded by a novel spot welding process for dissimilar metal lap joints using a new tool with the tip made of spherical ceramics, i.e. ‘Friction Anchor Welding.’ As a result, the rotating tool was plunged only to 1.3–1.4 mm from the Al alloy surface, and accordingly, a steel projection was not formed in the Al alloy sheet. Further, the Al alloy near the rotating tool was removed. However, near this removed area, the Zn layer on the GI steel melted and was removed by friction heat, and consequently, the GI steel and the Al alloy were welded. Thus, the tensile shear strength reached about 2.6 kN/point.     

钛/钢异种金属焊接的研究现状

实现钛与钢异种金属间的有效连接比较困难。为了探寻钛/钢的有效连接方法,在分析钛/钢异种材料的焊接性基础上,对钛/钢异种金属间的激光焊、电子束焊、激光-电弧复合焊等研究现状进行探讨。生成于接合界面的脆性金属间化合物是严重限制钛/钢异种金属接头性能的主要因素;选用合理的焊接工艺和添加适宜的中间层是实现钛/钢有效连接的重要途径。提出采用双层或多层金属的中间层来抑制界面金属间化合物生成是今后的研究方向。     

镍基合金复合钢板的焊接

环化塔预热器壳体的设计材料是Hastelloy C-276、Monel 400两种镍基合金复合不锈钢板,焊接是制造这台设备的关键技术.通过分析镍基合金复合钢板的焊接特点,指出镍基合金复合钢板焊接的关键是控制基层根部焊接时,焊缝金属中不要熔入复层合金成分;复层堆焊后的合金成分接近或达到焊材的化学成分,满足耐蚀要求.采用台阶式坡口形式,是避免根部焊缝金属互熔的最好措施;控制焊接线能量的多层焊是保证堆焊复层耐蚀性的关键.     

Modelling rotary friction welding of VZh175 high creep strength nickel alloy

The technological parameters of rotary friction welding of VZh175 nickel superalloy with high creep resistance and subjected to different heat treatment were investigated. The second-order polynomials are derived. The ranges of the optimum parameters of rotary friction welding are determined.     

Seal spot welding of steel and aluminium alloy by resistance spot welding: dissimilar metal joining of steel and aluminium alloy by Zn insertion

This research concerns a dissimilar metal joining of steel and aluminium (Al) alloys by means of zinc (Zn) insertion. The authors propose a joining concept for achieving strong bonded joints between Zn-coated steel and Al alloys. A eutectic reaction between Zn in the Zn coating and uniform Al–Fe intermetallic compound (IMC) layer at the joint interface, leading to a strong bonded joint. The ultimate aim of this research was to apply this joining concept in the resistance spot welding process for manufacturing vehicle bodies. As a practical issue characteristic to joints of dissimilar metals, anticorrosion measures against electrochemical corrosion must be undertaken. If there is moisture near a joint interface of dissimilar metals, electrochemical erosion will progress. Therefore, a sealing function that could prevent moisture intrusion is required. By applying the above-mentioned welding process to a set of metals with thermosetting resin spread in between, we realized seal spot welding, which not only prevented moisture intrusion but also retained high tensile strength. In this research, first, a cyclic corrosion test was performed on the seal spot-welded joint of galvanized (GI) steel, a steel grade widely distributed in Japan, and Al alloy was bonded by seal spot welding, and the following topics are discussed. Complete removal of sealant from the joint interface is the key to realizing the high tensile stress joint, because remaining sealant will lead to reduction in tensile strength. Therefore, heat generation at the interface was monitored by measuring electrical current and potential difference between the two electrodes, and a precise temperature control was performed. Moreover, the bonding process was clarified by stepwise analysis of the joint interface using optical microscopy, and a guideline for producing strong joints was proposed. And finally, a TEM observation also confirmed that the interface structure of the seal spot-welded joint was the same as joints without the resin; a thin and uniform Al–Fe IMC layer was formed and a strong metallurgical bonding was achieved.     

Improving weld strength of magnesium to aluminium dissimilar joints via tin interlayer during ultrasonic spot welding

Abstract

Welding of magnesium to aluminium alloys is enormously challenging due to the formation of brittle Al₁₂Mg₁₇ intermetallic compounds (IMCs). This study was aimed at improving the strength of dissimilar joints of AZ31B-H24 magnesium alloy to 5754-O aluminium alloy by using a tin interlayer inserted in between the faying surfaces during ultrasonic spot welding. The addition of tin interlayer was observed to successfully eliminate the brittle Al₁₂Mg₁₇ IMCs, which were replaced by a layer of composite-like tin and Mg₂Sn structure. Failure during the tensile lap shear tests occurred through the interior of the blended interlayer as revealed by X-ray diffraction and SEM observations. As a result, the addition of a tin interlayer resulted in a significant improvement in both joint strength and failure energy of magnesium to aluminium dissimilar joints and also led to an energy saving because the optimal welding energy required to achieve the highest strength decreased from ～1250 to ～1000 J.     

Influence of aluminium alloy type on dissimilar friction stir lap welding of aluminium to copper

A heat-treatable (AA 6082) and a non-heat treatable (AA 5083) aluminium alloys were friction stir lap welded to copper using the same welding parameters. Macro and microscopic analysis of the welds enabled to detect important differences in welding results, according to the aluminium alloy type. Whereas important internal defects, resulting from ineffective materials mixing, were detected for the AA 5083/copper welds, a relatively uniform material mixing was detected in the AA 6082/copper welds. Micro-hardness testing and XRD analysis also showed important differences in microstructural evolution for both types of welds. TEM and EBSD-based study of the AA 5083/copper welds revealed the formation of submicron-sized microstructures in the stirred aluminium region, for which untypically high hardness values were registered.     

Effect of friction welding conditions on joint properties of austenitic stainless steel joints by friction stud welding

This study focuses on the opening mode of induction bends; this mode represents the deformation outside a bend. Bending experiments on induction bends are shown and the manner of failure of these bends was investigated. Ruptures occur at the intrados of the bends, which undergo tensile stress, and accompany the local reduction in wall thickness, i.e. necking that indicates strain localization. By implementing finite element analysis (FEA), it was shown that the rupture is dominated not by the fracture criterion of material but by the initiation of strain localization that is a deformation characteristic of the material. These ruptures are due to the rapid increase in local strain after the initiation of strain localization and suddenly reach the fracture criterion. For the evaluation of the deformability of the bends, a method based on FEA that can predict the displacement at the rupture is proposed. We show that the yield surface shape and the true stress–strain relationship after uniform elongation have to be defined on the basis of the actual properties of the bend material. The von Mises yield criterion, which is commonly used in cases of elastic–plastic FEA, could not predict the rupture and overestimated the deformability. In contrast, a yield surface obtained by performing tensile tests on a biaxial specimen could predict the rupture. The prediction of the rupture was accomplished by an inverse calibration method that determined the true stress–strain relationship after uniform elongation.     

铝合金与低碳钢的夹层电阻点焊接头特性

以钎料Al86Si6Mg8薄带为中间层对铝合金A6061与低碳钢Q235进行了点焊,观察分析了接合界面区反应层形貌及分布等微观组织结构特征,探讨了焊接电流、焊接时间与电极压力对熔核尺寸和接头抗剪力的影响。接头熔核直径与抗剪力随焊接电流、焊接时间的增加而增加,随电极压力的增大而降低,在19 k A的焊接电流条件下获得接头的抗剪力达到5.2 k N。试验结果表明,夹层的使用起到了抑制界面反应层生长和提高接头性能的效果。