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.     

Materials flow and phase transformation in friction stir welding of Al 6013/Mg

Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding (FSW) experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al₃Mg₂ and Al₁₂Mg₁₇, were formed sequentially at Al6013/Mg interface.     

Microstructural and mechanical properties of friction stir welded aluminum/copper lap joints

This paper focuses on the microstructural and mechanical properties of the friction stir welding (FSW) of 1060 aluminum alloy to a commercially pure copper. A number of FSW experiments were carried out to obtain the optimum mechanical properties by adjusting the rotational speed and welding speed in the range of 750–1500 rpm and 30–375 mm/min, respectively. Various microstructures with different morphologies and properties were observed in the stir zone. The results indicated that Al₄Cu₉, AlCu and Al₂Cu are the main intermetallic compounds formed in the interfacial region. The effect of formation of hard and brittle intermetallic phase at the interface of the joints on the shear strength of the joint is discussed.     

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.     

Effect of Preheating in Hybrid Friction Stir Welding of Aluminum Alloy

The controlled energy input into the system by introducing an extra heat source to enhance the material flow along with reduction of the plunging force remains a potential area of considerate for the development of hybrid friction stir welding (FSW) process. Hence, the effect of preheating on the weld joint properties is evaluated using plasma-assisted friction stir welding (P-FSW) process for joining aluminum alloy. A comparative study of mechanical and macro-microstructural characterizations of weld joint by FSW and P-FSW has been performed. Transverse tensile strength of weld joint is approximately 95% of base metal produced by P-FSW and is 8% more than conventional FSW welds. The effect of preheating enhances material flow and dissolution of fine oxide particles by plasma arc results in increase of strength and marginal modification of deformation behavior. The preheating brings uniformly distributed hardness in weld zone and the magnitude is higher in the advancing side with overall increase in average hardness value. Grain sizes are much finer due to the pinning effect of Al₂O₃ particles that retarded grain growth following recrystallization during P-FSW and thus led to more pronounced reduction in grain size and relatively brittle fracture during tensile loading of welded joint. Overall, the influence of preheating acts quite homogeneously throughout the structure as compared to conventional FSW. However, the results reveal that the development of P-FSW is still in initial stage and needs to improve in various aspects.     

Microstructural characterization and mechanical properties of aluminum 6061-T6 plates welded with copper insert plate (Al/Cu/Al) using friction stir welding

Friction stir welding was used to join two aluminum 6061-T6 plates with an insert of a pure copper plate (Al/Cu/Al), and then the influence of the copper insert on the joint performance was studied. The dissimilar welding results were also compared with AA 6061 friction stir welds produced without copper insert (Al/Al). Optical and scanning electron microscopes were used for the microstructural observations of the welded samples. X-ray diffraction analysis was used to analyze phase component of the Al/Cu/Al specimen. A defect-free joint was observed for the Al/Cu/Al joint at a rotational speed of 950 r/min and a welding speed of 50 mm/min. Microstructural observation of the weld nugget zone (WNZ) demonstrates the formation of composite-like structure which promotes metallurgical bonding of aluminum and copper. XRD results show the formation of intermetallic compounds (IMCs), such as Al₄Cu₉ and Al₂Cu. Furthermore, it was observed that the hardness of the weld with the Cu insert plate is higher than that of other samples due to more dislocation density and a distinct rise in hardness values was observed due to the presence of IMCs. The ultimate tensile strength of the joint with copper insert plate is higher than that of the other sample due to the strong metallurgical bonding between Al and Cu.     

轴肩尺寸对异种铝合金材料搅拌摩擦焊接头显微组织的影响规律

对5083铝/6082铝异种材料搅拌摩擦焊（friction stir welding,FSW）进行研究,重点分析轴肩直径对横截面形貌、显微组织与显微硬度的影响规律.结果表明,FSW接头焊核区由致密细小的等轴晶组成;增加轴肩直径可增加焊核区沿垂直焊缝方向的宽度以及增大焊核区、热影响区与热力影响区的晶粒尺寸.与后退侧的6082铝合金不同,前进侧5083铝合金的热力影响区发生了动态再结晶.显微硬度呈W形分布,最小值出现在热影响区.显微硬度的测试结果与焊核区的横截面形貌结果吻合.     

Microstructure evolution and microhardness of friction stir welded cast aluminum bronze

Microstructural characteristics and mechanical properties of a friction stir welded cast aluminum bronze (Cu–9Al–1Fe), produced by a sand casting method, have been investigated at tool rotation of 850–1500 rpm and traverse speed of 50–100 mm/min. Refinement of the primary coarse cast microstructure in the base metal was seen after friction stir welding. Microstructure of the stir zone was characterized in four distinct areas of non-isometric fine grains while a significant grain growth was noticed in some of the areas. Conditions of grain growth are defined with high heat input intensity and low heat transfer capability. The grain size was observed to decrease after FSW, resulting in a greater microhardness across the welded region from about 100 HV in the base metal to about 150 HV at the center of the stir zone. The increased hardness in the stir zone may have stemmed from the locally refined grain size according to Hall–Petch relation.     

Influence of tool material on mechanical and microstructural properties of friction stir welded 316L austenitic stainless steel butt joints

In the present research, the influence of friction stir welding (FSW) tool material on the mechanical and microstructural properties of friction stir (FS) welded 316L stainless steel butt joints is investigated. FS welds were produced using two different tungsten based FSW tools having identical tool shoulder and pin profiles. In both the cases, the FSW experimental runs were carried out using tool rotational speed of 600 rpm, welding speed of 45 mm/min, axial force of 11 kN and tool tilt angle of 1.5°. The results of the study show that the joints produced using the tungsten lanthanum oxide tool are having superior mechanical and microstructural properties when compared to the joints produced using tungsten heavy alloy tool. Furthermore, the tool degradation study by mass loss and photographic techniques suggests that the tungsten lanthanum oxide tool is more prone to degradation by plastic deformation, whereas the tungsten heavy alloy tool is more prone to degradation by wear.     

Influence of Processing Parameters on Induced Energy, Mechanical and Corrosion Properties of FSW Butt Joint of 7475 AA

Friction stir welding (FSW), a promising solid state joining process invented at TWI in 1991, was used to join 9?mm thick 7475 aluminum alloy which is considered essentially unweldable by fusion processes. In the present work, the process parameters such as tool rotational speed were varied from 300 to 1000?rpm for a travel speed of 50?mm/min and the influence of process parameters in terms of energy input on microstructure, hardness, tensile strength, and the corrosion property of 7475 aluminum joints was evaluated and analyzed. The maximum tensile strength of FSW joints was obtained at rotational speed of 400?rpm and traverse speed of 50?mm/min (59.2?kJ) which attributed maximum stirred zone area and maximum hardness. The maximum corrosion resistance properties of weld in 3.5% NaCl solution, however, were obtained at rotational speed of 1000?rpm and traverse speed of 50?mm/min. Furthermore, for a given weld, stirred zone showed improved corrosion properties than TMAZ.     

AA5083铝合金的搅拌摩擦焊接工艺参数对搅拌头受力和热输入的影响(英文)

采用系统实验设计方法研究AA5083铝合金搅拌摩擦焊接工艺参数对搅拌头受力和热量输入的影响,得到了用来设计搅拌摩擦焊搅拌头和焊机的经验模型。当采用计算机来控制搅拌摩擦焊接时,这些模型可用来确定AA5083这类铝合金的摩擦焊接工艺参数、编制焊接程序及工艺参数控制。结果表明:影响轴向力和热量输入的重要参数是搅拌头转速、焊接速度和搅拌头轴肩直径,而影响纵向应力的重要参数是焊接速度和探头直径。     

Three-dimensional friction stir welding using a high payload industrial robot

The present study investigates the friction stir welding (FSW) process of extremely curved surfaces using a high payload industrial robot. The welding process of aluminum alloys in a butt joint configuration has been investigated over convex surface radii ranging from 104.5 to 14.5 mm. The weld qualities of the produced joints have been assessed by macrographs and tensile tests. It was shown that the FSW process needs an optimization of the welding path as well as an optional adaptation of the process parameters in the curved region in order to produce sound and reproducible joints without inner or outer defects. The results contribute to further fields of application where non-linear welds have to be produced.     

The role of rotation speed on intermetallic compounds formation and mechanical behavior of friction stir welded brass/aluminum 1050 couple

In this paper, the intermetallic compounds formation during dissimilar friction stir welding of brass to aluminum 1050 and its effect on the mechanical behavior of joint were studied. Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy analysis (EDS) and X-ray Diffraction analysis were used to characterize intermetallics. In addition, tensile tests and microhardness measurements were performed to evaluate mechanical properties. The results showed that utilizing rotation speeds higher than 400 rpm leads to gradual formation of intermetallic compounds in the stir zone and at the interface. CuAl₂ is the dominant compound in the composite structure of the stir zone, whereas four intermetallic bands are detected at the interface. From aluminum to brass, two middle layers were formed. Then, CuAl₂, Cu₉Al₄ and CuZn were detected. The increase in rotation speed is accompanied by thickening and development of interfacial intermetallic compounds. The optimum rotation speed of 450 rpm yielded a narrow interfacial intermetallic compound and a lamellar composite structure within the stir zone which enhances the tensile strength of the weld. On the other hand, further increase of rotation speed lowers the tensile strength of the weld which is accompanied by disappearance of lamellar composite structure, increment of weld defects and thickening of interfacial intermetallic layer.     

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.     

Al-Li-Cu合金搅拌摩擦焊与TIG 焊接头组织及力学性能分析

组织分析表明,Al-Li-Cu TIG焊焊缝和搅拌摩擦焊焊核区均由等轴晶粒构成,但前者的晶粒尺寸较后者的大;TIG焊接头热影响区组织粗化程度较搅拌摩擦焊严重;搅拌摩擦焊接头内存在一独特的热机影响区,该区内的组织发生了较大程度的变形。实验结果表明铝锂合金搅拌摩擦焊可避免形成TIG焊时的凝固裂纹等缺陷。搅拌摩擦焊接头的力学性能优于TIG焊接头,二者的拉伸强度分别为393MPa和337MPa,延伸率分别为14．4％和6．6％。     

2219铝合金厚板搅拌摩擦焊搅拌头结构参数优化

为探究搅拌头几何形貌对2219铝合金厚板搅拌摩擦焊核心区温度场的影响，基于ABAQUS/CEL建立了18 mm厚2219铝合金FSW三维过程仿真模型，应用有限元分析法对焊接过程进行仿真研究，得到了焊接核心区测温点实时温度循环曲线。利用自主研发的热电偶测温系统对焊接温度场相应测温点温度进行检测，经过对比可知,不同转速试验和仿真数据曲线变化趋势基本相同，验证了所建立的FSW过程仿真模型的有效性。探究了搅拌头结构参数对FSW过程核心温度场的影响规律，针对搅拌头的轴肩尺寸、搅拌针锥角、轴肩凹角、螺纹升角等结构尺寸设计了4因素3水平正交试验。结果表明，轴肩直径对核心区温差的影响最为显著，当搅拌头的轴肩尺寸为36 mm、搅拌针锥角为6°、轴肩凹角为2.5°、螺纹升角为11°时，搅拌头结构尺寸较为合理，核心区温差值较小。 创新点： 探究了搅拌头几何形貌对搅拌摩擦焊核心区温度场的影响,实现了搅拌头的结构参数优化。     

Dissimilar friction stir welding between 5052 aluminum alloy and AZ31 magnesium alloy

Dissimilar friction stir welding between 5052 Al alloy and AZ31 Mg alloy with the plate thickness of 6 mm was investigated. Sound weld was obtained at rotation speed of 600 r/min and welding speed of 40 mm/min. Compared with the base materials, the microstructure of the stir zone is greatly refined. Complex flow pattern characterized by intercalation lamellae is formed in the stir zone. Microhardness measurement of the dissimilar welds presents an uneven distribution due to the complicated microstructure of the weld, and the maximum value of microhardness in the stir zone is twice higher than that of the base materials. The tensile fracture position locates at the advancing side (aluminum side), where the hardness distribution of weld shows a sharp decrease from the stir zone to 5052 base material.     

Effects of welding parameters and tool geometry on properties of 3003-H18 aluminum alloy to mild steel friction stir weld

Defect-free butt joints of 3003 Al alloy to mild steel plates with 3 mm thickness were performed using friction stir welding (FSW). A heat input model reported for similar FSW was simplified and used to investigate the effects of welding speed, rotation speed and tool shoulder diameter on the microstructure and properties of dissimilar welds. The comparison between microstructure, intermetallics and strength of welds shows the good conformity between the results and the calculated heat input factor (HIF) achieved from the model. The joint strength is controlled by Al/Fe interface at HIF of 0.2–0.4, by TMAZ at HIF of 0.4–0.8 and by intermetallics and/or defects at HIF>0.8.     

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.     

Microstructure evolution and fracture behaviour of friction stir welded 6061-T6 thin plate joints under high rotational speed

6061-T6 sheets with 0.8?mm thickness were successfully welded using high-speed friction stir welding (FSW) technology. The microstructural evolution and fracture behaviour of the joints were studied. The results show that sound joints could be obtained at the investigated high rotational speed of 8000?rev?min^?1 and welding speeds of 300–1200?mm?min^?1. Compared with conventional rotational speed, the grain size in the nugget zone (NZ) is obviously refined under high rotational speed. The Mg₂Si, Al₈Fe₂Si and Al₂CuMg precipitates reprecipitated adequately in the NZ during high-speed FSW, resulting in the number of the precipitates increased significantly, and further alleviating the weld softening. The difference in weld softening leads to different fracture characteristics during the tensile process. After artificial aging, the maximum welding softening in all joints is located in the heat affected zone, and the fracture is characterised by brittle fracture.