Effect of tool plunge depth on joint formation and mechanical performance of friction stir forming joints made between AA 5052-H32 and AA 6061-T6 sheet metals

The potential of friction stir forming for joining dissimilar grades of aluminum alloys namely, AA 5052-H32 and AA 6061-T6, was investigated. Study on the effect of tool plunge depth revealed that, lap shear load of 7.16 kN and cross-tensile load of 3.51 kN, recorded at medium tool plunge depth range from 0.5 to 0.7 mm, measured using a universal testing machine, were much larger than those of friction stir welded and friction stir spot welded joints fabricated on the same materials. Joint macrostructure observed with optical microscope revealed that joints were strengthened either by mechanical pin interlocking or by metallurgical bonding. The effect of tool plunge depth on the stir zone formation and the influence of frictional heat flux on the lower sheet were revealed through the microhardness measurement using Vickers hardness tester. Morphological studies revealed that tool plunge depth has a significant influence on the pin formation and the geometric features, generated in these joints. Occurrence of various failure modes such as pin pull-out, pin shear, partial bond delamination, and tear-off, were governed by the formation of critical weak zones at various tool plunge depths.     

根部螺纹搅拌针对搭接接头钩状缺陷和性能的影响

选用3 mm厚的7075–T6铝合金为研究对象,研究了根部带有螺纹的搅拌针对搅拌摩擦焊搭接接头钩状缺陷及拉剪载荷的影响. 结果表明,搅拌针上的螺纹可明显改变焊接过程中的材料流动;塑性材料在搭接面上部集中,挤压搭接界面,焊后搭接接头的钩状缺陷向下弯曲;搭接面处焊核区的宽度较搅拌针的直径明显增大. 因搅拌针端部无螺纹,焊接速度较大时接头底部会由于材料无法及时填充而产生孔洞缺陷. 随着搅拌头焊接速度的升高,搭接接头的拉剪载荷先上升后下降,最高载荷在焊接速度为40 mm/min时取得,为23.333 kN.     

Approach to disrupting thick intermetallic compound interfacial layer in friction stir brazing (FSB) of Al/Cu plates

Friction stir brazing (FSB) was developed for dissimilar joining to overcome the problems associated with friction stir lap welding (e.g. pin wear, narrow bonded area, hook defect) by metallurgical reaction instead of plastic flow. To enhance the thermomechanical effect of the rotating shoulder, a pin free tool with a large shoulder of 30 mm diameter was used in FSB of 5 mm thick Al/Cu plates in stepped lap configuration with Zn braze. Compared to the case using common tool of 20 mm diameter, it was found that although the intermetallic compound (IMC) layer grew thickly, it was disrupted into particles, and end crack within thick IMC layer was eliminated. As a result, the joint fractured not along interface and the fracture load increased by as much as 2271 N. This work proposed an approach to disrupting continuous IMC into particles by enhancing the mechanical effect of rotating shoulder.     

Orbital friction stir lap welding in tubular parts of aluminium alloy AA5083

In this study, orbital friction stir lap welding of 360?mm diameter AA5083-H321 tube to 350?mm diameter AA5083-O flange was investigated. The influence of rotational and travel speed of tool with triangular frustum pin on the metallurgical structure and mechanical properties of orbital friction stir lap welded samples were studied. The results indicated that defect free orbital lap joints are successfully obtained using tool rotational speed of 650 and 800?rev?min^?1 with a constant travel speed of 40?mm?min^?1. The strengthening mechanism in the stir zone is solid solution strengthening and dislocation looping. The maximum joint strength was achieved at a welding speed of 650?rev?min^?1 and 40?mm?min^?1. Failure of tensile shear test samples occurred far from the friction stir welding zone.     

Effects of pin diameter on microstructures and mechanical properties of friction stir spot welded AZ31B magnesium alloy joints

Abstract

The effects of pin diameter on the microstructure and mechanical properties of friction stir spot welded AZ31B magnesium alloy joints were investigated using microstructural observations, tensile tests and microhardness tests. The results showed that with an increase in the pin diameter, the height and width of the curved interface in the friction stir spot welded AZ31B magnesium alloy joints increased because of the strong effect of stirring and high temperature obtained when large sized pins were adopted. An increase in the pin diameter led to the coarsening of α-Mg grains in the stir zone, thermomechanical affected zone and heat affected zone because of heat generation, resulting in the decrease in microhardness of stir zone, thermomechanical affected zone and heat affected zone. The tensile shear force of the friction stir spot welded AZ31B magnesium alloy joints increased with the increase in pin diameter because the height and width of the curved interface dominated the failure of the specimens.     

High strength lap joint of aluminium and stainless steels fabricated by friction stir welding with cutting pin

Abstract

Dissimilar lap joints of aluminium and stainless steel were first friction stir welded by the tool with a cutting pin. The results showed that sound joints could be obtained by this method. When the pin was inserted into the lower steel sheet, macrointerlocks were formed by the steel flashes plugging into the upper aluminium at both sides of the nugget bottom. At the aluminium/steel interface, a thin intermetallic compound (IMC) layer and the mechanical bonding of microinterlocks were formed. In addition, the aluminium near the interface was also strengthened by grain refinement and IMC particles. Therefore, the beneficial effect of the macrointerlocks provided by the steel flashes was removed, the shear strength of the joint reached 89·7 MPa, which was even higher than that of the base metal of aluminium.     

Effect of Intermetallic Compound Phases on the Mechanical Properties of the Dissimilar Al/Cu Friction Stir Welded Joints

Types and distribution of intermetallic compound phases and their effects on the mechanical properties of dissimilar Al/Cu friction stir welded joints were investigated. Three different rotation speeds of 1000, 1200 and 1400 rpm were used with two welding speeds of 20 and 50 mm/min. The results show that the microstructures inside the stir zone were greatly affected by the rotation speed. Complex layered structures that containing intermetallic compound phases such as CuAl₂, Al₄Cu₉ were formed in the stir zone. Their amount found to be increased with increasing rotation speed. However, the increasing of the rotation speed slightly lowered the hardness of the stir zone. Many sharp hardness peaks in the stir zones were found as a result of the intermetallic compounds formed, and the highest peaks of 420 Hv were observed at a rotation speed of 1400 rpm. The joints ultimate tensile strength reached a maximum value of 105 MPa at the rotation speed of 1200 rpm and travel speed of 20 mm/min with the joint efficiency ranged between 88 and 96% of the aluminum base metal. At the travel speed of 50 mm/min, the maximum value of the ultimate tensile strength was 96 MPa at rotation speed of 1400 rpm with the joint efficiency ranged between 79 and 90%. The fracture surfaces of tensile test specimens showed no evidence for the effect of the brittle intermetallic compounds in the stir zones on the tensile strength of the joints.     

Effect of Tool Rotation Rate on Microstructure and Mechanical Behavior of Friction Stir Spot-Welded Al/Cu Composite

In this study, the friction stir spot welding of Al/Cu composite produced by accumulative roll-bonding process was performed using a triangular pin with no features. The influence of tool rotation rate on the microstructure, surface hardness, and tensile shear strength was examined. The results indicated that the weld made at lower tool rotation rate was not bonded because there was no intermixing between the upper and lower sheets. The maximum shear failure load increased with the increasing tool rotation rate, and reached a maximum value at 1400 rpm, which can be ascribed to the increasing area and effective length (d) of stir zone (SZ). The experimental observations showed the presence of the intermetallic compounds (Al₂Cu and AlCu₃) in the SZ. It was concluded that the intermetallic compounds, accompanied by the material crushing, increased the hardness of the SZ.     

Influence of tool thread on mechanical properties of dissimilar Al alloy friction stir spot welds

Abstract

The influence of threaded and wear simulated (half thread) tools on the mechanical properties of dissimilar Al alloy friction stir spot welds is investigated. With lower tool rotational speed settings, the failure loads of Al 5754/Al 6111 lap joints made using a threaded tool were clearly higher than that of a half thread tool. However, the failure load of the joints made using a half thread tool increased when the tool rotational speed increased, and finally, as the rotational speed was further increased, the failure load became almost the same as the failure load of joints made using a threaded tool. In Al 5052/Al 6061 butt joints made using the threaded and half thread tools, the area of the stir zone on the bonded cross-section corresponded with the actual bonded region on the fracture surface. Therefore, the thread on the rotating pin has limited influence on the mechanical properties of the friction stir spot lap joints.     

Study of friction stir joining of thin aluminium sheets in lap joint configuration

Abstract

Thinning in friction stir lap joints and its relation with the process variables was investigated. Friction stir welds were made on 1 mm thick AA6111 aluminium alloy sheets in order to study the effects of rotation rate, traverse speed, plunge depth, tilt angle and pin height on faying surface defects. Sheet thinning on the advancing and retreating sides was quantified and the lap shear strength of the joints was evaluated. A decrease in the pitch of the runs at constant rotation rate increased the sheet thinning and reduced the joint strength in a linear manner. Process pitch and pin height were found to be the most critical factors in determining the faying surface lift up. A pin of the same height as the sheet thickness resulted in maximum lap shear strength. Tool tilt did not show a significant effect on the sheet thinning.     

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。     

Microstructure,static and fatigue properties of refill friction stir spot welded 7075-T6 aluminium alloy using a modified tool

ABSTRACT

Defect-free joints were produced in 2.0?mm thick 7075-T6 Al alloy by refill friction stir spot welding using a modified tool. Weld performance was evaluated in terms of microstructure, interfacial bonding, hardness, static and fatigue strength based on the experimental observations. The results indicated that grain size, interfacial bonding quality and lap shear strength significantly depend on sleeve penetration depth (SPD), with sufficient interfacial bonding and stable lap shear strength achieved when SPD?≥?1.8?mm. The SPD and applied load played a dominant role in determining the static lap shear and fatigue failure mechanisms, respectively. More precisely, the lap shear failure mode was an interfacial failure when SPD?≤?1.8?mm, and nugget pullout when SPD?≥?2.0?mm. The fatigue fracture mode involved nugget pullout under high applied load, while fracture through the parent sheet occurs under medium and lower applied loads.     

摩擦增材辅助Ti/Al搅拌摩擦搭接接头特征分析

为解决Ti/Al异种材料搅拌摩擦焊接接头强度低、搅拌针磨损等问题,提出一种摩擦增材辅助搅拌摩擦搭接焊(friction addition-friction stir lap welding, FA-FSLW)技术. 该新工艺延续了固相连接的优势,具有热输入量低、界面金属间化合物薄等特点.文中研究了以6082铝合金作预沉积层辅助实现3 mm厚2A12铝合金板与4 mm厚TC4钛合金板之间的连接,焊接过程中搅拌头扎入铝沉积层而不接触钛表面,得到抗拉载荷最大为12.2 kN的接头.结果表明, FA-FSLW复合焊接头的界面迁移越大,接头承载越小.同时,发现界面处的Ti, Al元素发生了明显互扩散,Si元素在界面偏聚,与Ti, Al元素发生冶金反应后形成层状纳米级Ti-Al-Si金属间化合物,为提高接头强度奠定基础.     

Effect of second-phase particle on localized corrosion in Al–Zn–Mg–Cu–Mn alloy friction stir welded joint

The microstructure and corrosion behavior of a high-strength Al–Zn–Mg–Cu–Mn alloy friction stir welded (FSWed) joint were investigated using scanning electron microscope, transmission electron microscope, open-circuit potential test, and potentiodynamic polarization. The weld nugget zone and heat-affected zone (HAZ) of the FSWed joint showed diverse microstructural characteristics including micron-scale intermetallic particles and nanoscale precipitates, leading to different localized corrosion sensitivities. The results of electrochemical tests confirmed the regional difference of corrosion in FSWed joints. Detailed research on the corrosion process revealed that micron-scale Al(Fe,Mn,Si) particles promoted the dissolution of the vicinal matrix to induce pitting corrosion. The directionally distributed intermetallic particles and grain boundary precipitates in HAZ conduced to the development of intergranular microcracks into exfoliation. The matrix precipitates affected the localized corrosion tendency due to regional variation of the redissolution degree.     

Filling exit holes of friction stir welding lap joints using consumable pin tools

Abstract

In this study, filling friction stir welding was used to remove the exit hole of friction stir welding lap joints made from AA5456 sheets. For this purpose, the exit holes were filled by consumable pins with various geometries and different pin applying methods. Then, the structures and mechanical properties of the resulting joints were investigated. Results showed that the strength of 7% higher than the strength of the joint with the non-filled exit hole, ～91% of the corresponding defect free joints, is obtainable with this technique. The best results were found by a pin with 11° cone angle, 8?mm diameter and 7?mm length, and with a 6?mm plunge without rotation.     

Ti/Al异种合金搅拌摩擦焊搭接接头的界面特性(英文)

采用搅拌摩擦焊实现TC1钛合金和LF6铝合金异种材料的搭接连接,并对界面特性进行研究。采用所选取的工艺参数均能获得良好的表面成形,但每一种工艺参数下的界面形貌不同。随着焊接速度的增加或搅拌头转速的降低,被搅拌针搅入焊核区的钛合金粒子的数量减少,而且搭接接头的抗拉载荷也随着焊接速度的提高而降低。当焊接速度为60mm/min、搅拌头旋转速度为1500r/min时,接头的抗拉载荷达到最大值,此时的界面区可以分成三层。搭接接头的显微硬度分布不均匀,焊核中心区的显微硬度值最大,高达HV502。     

Investigation of microstructure and mechanical properties of friction stir lap jointed Monel 400 and Inconel 600

This study was conducted to investigate the microstructure and mechanical properties of friction stir lap joints. Monel 400 and Inconel 600 were selected as the experimental materials, and friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. The application of friction stir welding to Monel 400 effectively reduced the grain size in the stir zone; the average grain size of Monel 400 was reduced from 11.9 μm in the base material to 4.2 μm in the stir zone, which resulted in an improvement in the mechanical properties of the stir zone. The joint interface between Monel 400 and Inconel 600 showed a relatively sound weld without grooves or cracks, and only a small amount of voids with a size of 0.5 μm; however, no intermetallic compounds were observed in the lap jointed interface. Moreover, the hook on the advancing side of Monel 400 was formed from Inconel 600, which contributed to maintenance of the tensile strength. The evolution of microstructures and mechanical properties of friction stir lap jointed Monel 400 and Inconel 600 are also discussed herein.     

Remote method of controlling crack propagation in materials and welded joints

A TRIP 800 steel was friction stir spot welded using three different tool rotational speeds, 1600, 2000 and 2400 rpm, and the dwell time was kept constant at 2 s. The resultant microstructures formed in each weld zone were analysed as well as their hardness. Higher hardness values were observed for the lowest rotational speed, 1600 rpm, where the heat input in theory was lower and, therefore, the cooling rate was faster. However, for this rotational speed, allotriomorphic ferrite was also observed in the stir zone. In the lap shear tests, samples welded at 1600 and 2400 rpm did not reach the minimum value recommended by the AWS D8.1M standard, which was attributed to the lower bonding ligament length and also lower distance between the keyhole left by the pin and the end of the zinc line, which is formed in the stir zone. The fracture of the samples occurred along this line. As a result, the influence of the microstructure on the failure process could only be inferred when the zinc line disappeared.     

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.     

Analysis of tool geometry in dissimilar Al alloy friction stir welds using optical microscopy and serial sectioning

Abstract

The influence of tool geometry on material flow during friction stir welding of dissimilar aluminium alloys is investigated. Sheets of Al 2024 and Al 6061 alloys are friction stir welded in lap and butt configurations using different welding conditions. Optical microscopy with serial sectioning is utilised to systematically study material flow when small variations are made to the tool pin. It is shown that three flat features on the pin impose vertical material flow which can promote intermixing. When a threaded tool is used, the material flow and formation of the intermixed region depends on the orientation of the base materials, since the differences in viscosity of material on the advancing versus retreating side of the tool will inhibit intermixing. Decreasing the travel speed will promote intermixing by increasing the residence time to compensate for the differences in material viscosity that otherwise limit intermixing.