扩散时间对Al/Cu真空扩散连接的影响

采用真空扩散焊工艺对Al/Cu异种材料进行连接,研究了保温时间对接头微观组织及力学性能的影响.利用扫描电镜和EDS对焊接接头的微观组织及元素扩散行为进行了研究.结果表明:随着扩散时间的延长,接头的抗拉强度随之升高,焊接接头最高抗拉强度为185 MPa.     

β转变组织TA15钛合金的流动软化行为EI北大核心CSCD

利用等温压缩实验研究了β转变组织TA15钛合金在变形温度750~950℃、应变速率0.001~10 s^(−1)范围内的流动软化行为,定量分析了变形热效应和微观组织演变对流动软化行为的影响。结果表明:变形热效应是β转变组织TA15钛合金流动软化的重要机制,变形热软化程度随着变形温度的下降和应变速率的增大而增强,最高占到总流动软化程度的48.2%;动态再结晶、动态回复和流动失稳缺陷等形式的微观组织演变是流动软化的主要机制。基于动态材料模型,利用应变速率敏感性指数预测了3种微观组织演化形式主导的软化区域,并通过微观组织观测进行了验证。     

高熔点材料的搅拌摩擦焊接技术

通过焊具设计、接头微观组织与性能、焊接温度场和残余应力、热源辅助的搅拌摩擦焊(FSW)几个方面,全面介绍了高熔点材料搅拌摩擦焊技术的研究现状.结果表明,合适的搅拌头材料为钨铼(W-Re)合金和多晶立方氮化硼(PCBN);采用合适的焊具设计和工艺参数,可以得到具有良好微观组织、高强度的FSW接头;在模拟搅拌摩擦焊温度场和接头残余应力时,应依据焊接过程实际进一步完善物理模型;引入辅助热源有利于高熔点材料焊缝成形并提高焊具使用寿命.     

Cu/Al异种材料真空扩散连接研究

采用真空扩散连接工艺对Cu/Al异种材料进行连接,焊后利用扫描电镜和EDS对焊接接头的微观组织及元素扩散行为进行了研究.在焊接温度为540℃、扩散时间为60 min、焊接压力为5MPa的工艺下,焊接接头最高抗拉强度为185 MPa.     

Mg/Cu异种材料共晶反应钎焊连接研究

采用共晶钎焊工艺对Mg/Cu异种材料进行连接,焊后利用扫描电镜和EDS对焊接接头的微观组织及元素扩散行为进行了研究.在焊接温度为500℃,焊接时间为5min,焊接压力为2MPa的工艺下,焊接接头最高抗拉强度为42 MPa.     

4YQ690级埋弧焊焊接材料国内外对比试验

采用国内外两种4YQ690级埋弧焊接材料分别进行了熔敷金属及焊接接头性能试验,对两种焊接材料熔敷金属的化学成分、力学性能及焊接接头的微观组织及力学性能进行了分析研究。结果表明:通过对比国内外两种焊接材料发现熔敷金属化学成分设计上有一定差异,但焊缝金属的微观组织及力学性能接近;在设定的工艺条件下焊接WQ690E钢板,焊接接头各项性能全面满足ABS及CCS船级社规范中4YQ690级的相关要求。     

2219铝合金搅拌摩擦焊“弱连接”缺陷的制备及表征

搅拌摩擦焊焊缝金属的塑性流动与工件表面状态对焊缝的微观组织演化及焊缝缺陷形成有着十分重要的影响,采用"示踪铜箔"探索了可视化示踪材料紫铜箔在搅拌摩擦焊接头内的迁移行为。为进一步分析和证明搅拌摩擦焊接头"弱连接"缺陷形成机制,进行了2219铝合金(阳极化处理)的搅拌摩擦焊试验。结果表明,焊件表面未清理的氧化膜在搅拌摩擦接头内形成了一条始于后退侧、而在前进侧取向发生逆向延伸的黑色流动迹线,即"S"线弱连接缺陷。     

加载方式对Cu/Al真空扩散连接的影响

采用恒压和脉冲加压两种加压方式下的真空扩散连接工艺对Cu/Al异种材料进行连接,利用扫描电镜和EDS对焊接接头的微观组织及元素扩散行为进行了研究.在焊接温度为540℃、扩散时间为60 min、焊接压力为2～5MPa的工艺下,焊接接头最高抗拉强度为197MPa.     

304/Q345R复合板焊接接头微观组织及残余应力

为研究复合板在焊接过程中复杂的热力学行为,利用ABAQUS有限元软件对304/Q345R复合板的焊接过程进行了数值模拟,通过热电偶和盲孔法获得了焊接接头的热循环曲线和残余应力分布规律,验证了有限元模型的正确性. 同时采用光学显微镜和扫描电镜对焊接接头的微观组织、晶粒形貌和元素分布进行了分析,研究焊接接头部位的微观组织演化规律. 结果表明,焊接残余应力最大值为312 MPa,位于焊趾附近,残余应力沿焊缝至母材方向逐渐降低并趋于稳定. 在两种材料的交界面处发现残余应力不连续现象. 焊接接头微观组织主要由奥氏体和铁素体组成,复层熔合线附近的铁素体以板条状和针状形成带状过渡区,而熔合线附近的奥氏体晶粒成柱状形貌且尺寸更为微小.     

超声功率对2219-T351铝合金搅拌摩擦焊接头组织与性能的影响

采用搅拌摩擦焊和不同功率的超声辅助搅拌摩擦焊对2219-T351铝合金进行焊接试验,测量焊接温度和焊接压力,对焊接接头的微观组织、显微硬度和力学性能进行分析,研究了加入不同超声功率后焊缝的组织性能和材料流动性. 结果表明,超声能降低焊接温度,随着超声功率增加减小的幅度越大. 加入了超声后,焊缝微观组织更加均匀,底部材料的流动情况得到改善,焊缝区有更多的强化相残留,焊接接头的显微硬度、抗拉强度及断后伸长率在加入超声后均有提高,在加入2.25 kW的超声功率时达到最高,最高拉伸强度为331 MPa,可达到母材的80%左右.     

Microstructural mapping of friction stir welded AA 7075-T6 and AlMgSc alloys using electrical conductivity

Abstract

AlMgSc and AA 7075-T6 alloys find applications in the aeronautic industry due to their lightweight associated with high mechanical strength and fatigue resistance. Both alloys have poor weldability when joined by fusion welding processes, which is overcome with the use of friction stir welding (FSW). Recent research work shows that electrical conductivity field analysis can be used as a material characterisation technique for solid state material welding exhibiting a microstructure gradient. This study aims to apply electrical conductivity field analysis to bead on plate FSW to identify the potential application of this technique to map and characterise microstructural transformations. The FSW was conducted on AlMgSc and AA 7075-T6 plates with different parameters, and electrical conductivity measurements were performed at half thickness, complemented by other techniques as hardness, scanning electron microscopy and energy dispersive spectroscopy. A good correlation was observed among electrical conductivity field, microstructure and hardness of different zones in FSW beads.     

Review on underwater friction stir welding: A variant of friction stir welding with great potential of improving joint properties

Friction stir welding (FSW) is a solid-state welding process which is capable of joining materials which are relatively difficult to be welded by fusion welding process. Further, this process is highly energy-efficient and environmental-friendly as compared to the fusion welding. Despite several advantages of FSW over fusion welding, the thermal cycles involved in FSW cause softening in joints generally in heat-treatable aluminum alloys (AAs) due to the dissolution or coarsening of the strengthening precipitates leading to decrease in mechanical properties. Underwater friction stir welding (UFSW) can be a process of choice to overcome these limitations. This process is suitable for alloys that are sensitive to heating during the welding and is widely used for heat-treatable AAs. The purpose of this article is to provide comprehensive literature review on current status and development of UFSW and its importance in comparison to FSW with an aim to discuss and summarize different aspects of UFSW. Specific attention is given to basic principle including material flow, temperature generation, process parameters, microstructure and mechanical properties. From the review, it is concluded that UFSW is an improved method compared with FSW for improving joint strength. Academicians, researchers and practitioners would be benefitted from this article as it compiles significantly important knowledge pertaining to UFSW.     

Friction stir welding of aluminium 7136-T76511 extrusions

Abstract

This research programme evaluates the as welded properties of Al 7136-T76511 extrusions joined through friction stir welding (FSW). Microstructural characterisation and mechanical testing were performed on the baseline material and on panels friction stir welded at 250 and 350 rev min^–1 (all other weld parameters held constant). Transmission electron microscopy revealed the microstructural features in each of the unique weld regions and demonstrated that the precipitate density and morphology in these regions correlates with the temperature profile produced by the FSW process. A thermal model of FSW is developed that utilises an energy based scaling factor to account for tool slip. The slip factor is derived from an empirical relationship between the ratio of the maximum welding temperature to the solidus temperature and energy per unit length of weld. The thermal model successfully predicts the maximum welding temperatures and profiles over a range of energy levels. The mechanical behaviour after welding is correlated to the temperature distribution predicted by the model and to the observed microstructural characteristics. As welded mechanical properties of the alloy trended positively with the energy per unit length of weld, i.e. the highest joint efficiency was achieved at the highest welding temperature.     

Critical review on friction stir welding of aluminium to copper

The status quo of aluminium-to-copper joining by friction stir welding (FSW) drastically changed in recent years, as a result of the increased interest of the scientific community on this subject. Actually, since 2006 a large increase in the number of research groups addressing Al–Cu FSW has been witnessed all over the world, together with a significant increase in the amount of published studies. A chronological perspective on the evolution in Al–Cu FSW research is provided in this work, highlighting the pioneer and original contribution of several researchers to the current knowledge on the subject. Detailed and comprehensive investigations on the material flow mechanisms, the phenomena governing the formation and distribution of intermetallic phases during Al–Cu FSW, their relations with the welding parameters and their impact on the morphological, structural and mechanical properties of the welds are thoroughly discussed. The main findings reported in the literature are summarised in thematic tables.     

搅拌头机械载荷在搅拌摩擦焊接中的作用的数值分析

利用数值模拟技术分析搅拌头机械载荷在焊接过程中的作用,通过对比只考虑热载荷,考虑热载荷和搅拌头的下压力,综合考虑热载荷、搅拌头下压力和工作扭矩三种条件下的应力,应变和变形,结果发现,搅拌头下压力使焊后残余应力值大幅下降;搅拌头的工作扭矩是焊后残余应力、应变不对称分布的重要影响因素;并且搅拌头机械载荷使得薄板焊后残余变形的模式发生了完全相反的变化,由不考虑搅拌头载荷时的马鞍状变成了反马鞍状.     

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.     

Review of research progress on aluminium–magnesium dissimilar friction stir welding

The paper critically assesses the research progress towards aluminium–magnesium dissimilar friction stir welding (FSW). First, the theoretical requirements are explored through the understanding of joining mechanism and heat generation in aluminium–magnesium FSW. Next, the observed trends in microstructural characterisation and mechanical properties are analysed. Finally, the effects of welding parameters and how it influences process variables and materials responses are discussed in detail, and several suggestions are made based on these discussions.     

Three-dimensional numerical and experimental investigation on friction stir welding processes of ferritic stainless steel

A three-dimensional thermomechanical simulation of friction stir welding (FSW) processes is carried out for ferritic stainless steel by utilizing an Eulerian finite volume method under the steady state condition, and the simulation result is compared directly with both the measured temperature histories during FSW and the microstructural changes after FSW. Based on a viscoplastic self-consistent approach for polycrystal, the texture development in the FSWed material is determined from the velocity gradients along the streamlines in the material flow field. The simulation results show that the heat is generated mainly near the interface between the tool and the workpiece, and that the viscosity changes drastically in the vicinity of the boundary between the stir zone and the thermomechanically affected zone. From the predicted streamlines, it can be indicated that the strong material flow mainly develops on the retreating side of the tool. Also, the simulation results show that the shear deformation texture is significantly developed in the FSWed region. The measured temperatures and microstructural characteristics agree fairly well with the predicted data.     

Friction-stir lap-joining of aluminium-magnesium/poly-methyl-methacrylate hybrid structures: thermo-mechanical modelling and experimental feasibility study

In this research, the feasibility of friction-stir welding (FSW) for dissimilar lap-joining of an aluminium-magnesium alloy (AA5058) and poly-methyl-methacrylate sheets to attain sound and defect-free joints was examined. The inter-mixing flow patterns between the metal and polymer counterparts during FSW were predicted by employing three-dimensional finite element models. It is shown that the bonding mechanism between the dissimilar materials is mechanical interlocking at the interface which controls the joint strength depending on the processing parameters. The most suitable dissimilar lap-joining regarding microstructural soundness is attained at w=?1600?rev?min^?1 and v?=?25?mm?min^?1. Under this condition, the maximum joint strength, which is about ～60% of the weakest base material, is attained. Fractography indicates that the rupture occurs from the aluminium side.