Low-cycle fatigue of a friction stir welded 2219-T62 aluminum alloy at different welding parameters and cooling conditions

Strain-controlled low-cycle fatigue tests and microstructural evaluation were performed on a friction stir welded 2219-T62 aluminum alloy with varying welding parameters and cooling conditions. Cyclic hardening of friction stir welded joints was appreciably stronger than that of the base material. The cyclic stress amplitude increased, and plastic strain amplitude and fatigue lifetime slightly decreased with increasing welding speed from 60 to 200 mm/min but were only weakly dependent of the rotational rate between 300 and 1,000 rpm with air cooling. Friction stir welded joints with water cooling had higher stress amplitude and fatigue life than that with air cooling. Fatigue failure of the joint occurred in the HAZ where the soft zone was present, with crack initiation from the specimen surface or near-surface defect and crack propagation characterized by typical fatigue striations.     

Effective predictions of ultimate tensile strength,peak temperature and grain size of friction stir welded AA2024 alloy joints

A series of welds were made by friction stir welding (FSW) under different welding and rotation speeds. A 2D ultimate tensile strength (UTS) map was developed based on various experimental data to predict the UTS of friction stir welded AA2024 alloy joints. The accuracy of the UTS map was evaluated by comparing the estimated UTS with the corresponding experimental results from the FSW of the same material available in the open literature. Analytical models were developed to estimate the peak temperature and grain size in the nugget zone. The predicted optimal peak temperature and welding and rotation speeds for AA2024 were within the windows of 400–465 °C, 175–350 mm/min and 800–1,200 rpm, respectively, under which the joint tensile strength could be higher than 458 MPa (about 94.6 % of the base metal) and the estimated average grain sizes in the nugget zone were about 2–3.9 μm.     

Friction stir butt welding thin aluminum alloy sheets

0.8-mm-thick alclad 2024-T4 aluminum alloy sheets were friction stir butt welded. A 15-mm diameter shoulder tool was used to guarantee sufficient heat input during welding. A 0.08-mm shoulder plunge depth was adopted to reduce sheet thickness reduction. Sound joints were obtained at rotating speeds from 400 to 1000 rpm and welding speeds from 50 to 150 mm/min. A thickness reduction of 6% was achieved at 1000 rpm and 50 mm/min. Secondary phases firstly precipitated at the black lines in the stir zone (SZ). The hardness of the SZ showed a decrease about 6% compared with the base metal. A maximum tensile strength of 399.5 MPa and an elongation of 5.6% were achieved at 1000 rpm and 150 mm/min. The fracture morphologies showed typical ductile fracture mode.     

Design of tool system for the external nonrotational shoulder assisted friction stir welding and its experimental validations on 2219-T6 aluminum alloy

The nonrotational shoulder assisted friction stir welding (NRSA-FSW) is still in the feasibility study stage. To reveal details in the tool system designing and highlight advantages of this novel technology, the tool system for the NRSA-FSW was designed and utilized to weld high-strength aluminum alloy 2219-T6 for validations. Compared with the joints welded by the friction stir welding (FSW) without assistance of the nonrotational shoulder (NRS), the effect of the NRS on the weld formation and mechanical properties was illustrated. At a constant welding speed 100 mm/min, defect-free joints can only be obtained at the tool rotation speed 800 rpm by the FSW without assistance of the NRS, but the NRSA-FSW can produce defect-free joints in a wider range of tool rotation speeds 600–900 rpm. The NRS prevented all plasticized materials from escaping from the stirring zone, thus the weld nugget zone transformed from the basin-type formation to the spherical formation with increasing of the stirring effect when the tool rotation speed increased gradually. For joints welded by these two FSW processes, both the tensile strength and the elongation showed nearly the same trend with the tool rotation speed, but the NRSA-FSW can produce joints with the maximum tensile strength in a wider range. Compared with the maximum joint efficiency 71.2 % of the FSW without assistance of the NRS, the maximum tensile strength obtained by the NRSA-FSW also reached 69.0 % of the base material. All tensile specimens machined from defect-free joints fractured at the weakest region with minimum Vicker’s hardness; while for those joints with cavity defects, the fracture occurred at the defect location.     

Mechanical properties of friction stir welding and metal inert gas welding of Al-Zn aluminum alloy joints

In this work, an Al-Zn aluminum alloy was welded using friction stir welding (FSW) and metal inert gas (MIG) welding methods. The comparison between microstructure and mechanical properties of the two different joints was mainly discussed. Results showed that defect-free joints can be obtained using both the two welding methods. Due to much less heat input, grains of the stir zone (SZ) of the FSW joint are finer than those of the MIG joint, resulting into higher hardness. Tensile strength of the MIG and FSW joints respectively reaches 68.6 and 73.2% of the BM. The FSW joints own much better fatigue properties than the MIG joints and reach its infinite life at using 90 MPa. The FSW joint owns two cracks during the fatigue test.     

Friction stir welding of AZ61A magnesium alloy

This paper deals with the development of an empirical relationship to predict tensile strength of friction stir welded AZ61A magnesium alloy. The process parameters such as tool rotational speed, welding speed, axial force and tool pin profile play a major role in deciding the tensile strength. The response surface method (RSM) was used to develop the empirical relationship. The four-factor, five-level central composite design was used to minimize the number of experimental conditions. The developed empirical relationship can be effectively used to predict tensile strength of friction stir welded AZ61A magnesium alloy joints at 95 % confidence level.     

Influences of rotation speed on microstructures and mechanical properties of 6061-T6 aluminum alloy joints fabricated by self-reacting friction stir welding tool

A 6061-T6 aluminum alloy was self-reacting friction stir welded by using the specially designed tool with unequal shoulder diameters at a constant welding speed of 150 mm/min to investigate the effect of rotation speed on microstructure and mechanical properties of the joints. Excessive flash on the bottom surface of the joint and groove defects on both surfaces of the joint were formed when the lower shoulder diameter was much smaller. The suitable shoulder sizes were determined as 16 and 18 mm in lower shoulder diameter and upper shoulder diameter, respectively. The grain size and the dislocation density in the weld nugget zone (WNZ) increased with increasing rotation speed. The tensile strength of joints first increased with increasing rotating speed and then decreased remarkably as a result of the formation of void defect. The joints welded at lower rotation speeds were fractured in the thermal mechanically affected zone (TMAZ). However, the fracture locations of the defect-free joints were changed to the heat affected zone (HAZ) at higher rotation speeds.     

Friction stir welding characteristics of 2219-T6 aluminum alloy assisted by external non-rotational shoulder

Friction stir welding (FSW) of 2219-T6 aluminum alloy assisted by external non-rotational shoulder was carried out, and effects of the welding speed on microstructures and mechanical properties were investigated in detail. Defect-free joints were obtained in a wide range of welding speeds from 50 to 300 mm/min. The microstructural deformation and weld formation were dominated by the rotating tool pin and subsize concave shoulder but the non-rotational shoulder exerted very little effects for all joints. Compared with the weld obtained by conventional FSW, less intense stirring effects in FSW assisted by external non-rotational shoulder can only generate a narrower thermomechanically affected zone, whose width decreased with increasing of the welding speed. Microstructures and Vickers hardness distributions showed that this new welding process is beneficial to improving the asymmetry and inhomogeneity, especially in the weld nugget zone. The maximum tensile strength was up to 69 % of the base material.     

Effect of welding processes on tensile properties of AA6061 aluminium alloy joints

The present investigation is aimed at to study the effect of welding processes such as GTAW, GMAW and FSW on mechanical properties of AA6061 aluminium alloy. The preferred welding processes of these alloys are frequently gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) due to their comparatively easier applicability and better economy. In this alloy, the weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often causes inferior weld mechanical properties and poor resistance to hot cracking. Friction stir welding (FSW) is a solid phase welding technique developed primarily for welding metals and alloys that heretofore had been difficult to weld using more traditional fusion techniques. Rolled plates of 6 mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used for joining the plates is AA4043 (Al-5Si (wt%)) grade aluminium alloy. In the present work, tensile properties, micro hardness, microstructure and fracture surface morphology of the GMAW, GTAW and FSW joints have been evaluated, and the results are compared. From this investigation, it is found that FSW joints of AA6061 aluminium alloy showed superior mechanical properties compared with GTAW and GMAW joints, and this is mainly due to the formation of very fine, equiaxed microstructure in the weld zone.     

Predictions of the optimized friction stir welding process parameters for joining AA7075-T6 aluminum alloy using preheating system

The scope of this investigation is to evaluate the effect of welding parameters on the mechanical properties and microstructural features of 3-mm-thick AA7075-T6 aluminum alloy subjected to gas heating system as a preheating source during friction stir welding. Toward this end, a gas heating system was designed to heat up the weld seam just ahead of rotating tool to soften the material before being stirred. Three welding parameters, five levels, and a central composite design (CCD) have been used to minimize the number of experimental conditions. The joining parameters such as tool rotational speed, welding speed, and shoulder diameter have a significant influence on determining the mechanical properties of the welded joints. It was found that using preheating system mostly can result in higher total heat input into the weld joint and effectively reduces the formation of defects when unsuitable process parameters were used. Also, an attempt has been made to establish the mathematical model to predict the tensile strength and microhardness of the joints. The optimal welding conditions to maximize the final responses were investigated and reported. The results show that the joint fabricated at a rotational speed of 1,050 rpm, welding speed of 100 mm/min, and shoulder diameter of 14 mm exhibited higher mechanical properties compared to other joints.     

Investigation on the effects of SiC particle addition in the weld zone during friction stir welding of Al 6351 alloy

The International Journal of Advanced Manufacturing Technology - This study attempts to incorporate SiC particles in the weld zone during friction stir welding of Al 6351 alloy. SiC particles of...     

热处理对TC11/LF6异种金属摩擦焊质量的影响

对TC11/LF6钛铝异种金属进行了连续驱动摩擦焊接工艺及其焊后热处理工艺的研究,观察了热处理前后焊接接头焊合区微观组织并测定了试样力学性能。研究结果表明：未经热处理的焊接接头晶粒较为粗大,有明显的晶间化合物产生,接头显微硬度较高;经280℃退火1h后,焊接接头晶粒均匀细化,焊接界面产生较薄的不连续扩散层;热处理后接头晶粒明显细化,抗弯强度提高10.7%,显微硬度下降38%。通过组织和力学性能综合分析,得到最优化的TC11/LF6连续驱动摩擦焊接工艺参数。     

Investigations of friction stir welding process using finite element method

The aim of this study is to investigate the process of friction stir welding (FSW) by using finite element method (FEM). Currently, the materials that are difficult to be joined with conventional fusion methods can now be easily joined with the method of friction stir welding. In this paper, the welding capability of many different materials with this method has been investigated by using analytical and numeric methods. In this study, a finite element (FE) model was developed for welding process with friction stir welding of AZ31 magnesium alloy. This model was performed by the software of DEFORM 3D finite element in 960, 1,964, and 2,880 rpm rotational speeds and in 10 and 20 mm?min^?1 transverse speeds. The temperature values taken from experiments and the temperature values with FEM are compared, and according to these results, it can be stated that the FE model gives reasonable results with experimental results based on temperatures values. Hence, the FE model can be used to predict other parameters of FSW process in future studies.     

Influences of tool pin profile and axial force on the formation of friction stir processing zone in AA6061 aluminium alloy

AA6061 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio and good corrosion resistance. Compared to the fusion welding processes that are routinely used for joining structural aluminium alloys, the friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force etc., and the tool pin profile plays a major role in deciding the weld quality. In this investigation an attempt has been made to understand the effect of axial force and tool pin profiles on FSP zone formation in AA6061 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded cylindrical, triangular and square) have been used to fabricate the joints at three different axial force levels. The formation of FSP zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with the FSP zone formation. From this investigation it is found that the square tool pin profile produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.     

Improving joint features and tensile shear properties of friction stir lap welded joint by an optimized bottom-half-threaded pin tool

To increase the lap shear failure load of friction stir lap welding (FSLW) joint, a tool with a bottom-half-threaded pin was designed in the present study. Using 7N01-T4 aluminum alloy as the research object, tools with the bottom-half-threaded pin and the traditional full-threaded pin were used to fabricate lap joints. Results showed that the thread end position on the pin greatly influenced the material flow behavior. The material concentrated zone using the bottom-half-threaded pin mainly located above the lap interface, which is beneficial to suppress the hook and cold lap. The lap shear failure load of the FSLW joint using the bottom-half-threaded pin was 17,644.7 N, which is equal to 122.8 % of the joint using the full-threaded pin.     

AZ31B镁合金搅拌摩擦焊焊接工艺研究

采用搅拌摩擦焊对AZ31B镁合金板材进行了焊接试验,研究了搅拌头旋转速度、焊接速度和搅拌头轴肩下压量对焊接接头成形质量的影响。结果表明,搅拌头转速过快或焊接速度过慢时,焊缝会出现局部过热甚至熔化现象;反之,当搅拌头转速不够或焊接速度过快时,材料不能充分流动,会形成隧道型缺陷或表面沟槽。当搅拌头轴肩下压量过小时,焊缝内部组织疏松或出现孔洞、隧道型缺陷,焊缝表面出现沟槽,甚至使焊缝金属液外溢;搅拌头轴肩下压量过大,会造成摩擦力及搅拌头前移阻力增大、焊缝凹陷及出现飞边。当搅拌头转速为1200～1500r／min、焊速为30～60mm／min,搅拌头轴肩下压量为1．5～2．0mm时,可得表面成形良好、内部无孔洞和隧道的焊缝。     

硫酸阳极化机箱搅拌摩擦焊结构设计及工艺研究

为了提高机箱焊缝的致密性,减少硫酸阳极化后机箱焊缝露白、槽液残留等问题,文中从铝合金机箱的结构特点入手,详细介绍了机箱搅拌摩擦焊结构和焊接夹具的设计要点、焊接和热处理的工艺参数等。通过样件的试生产和试验验证,模拟样件焊接接头的抗拉强度超过母材的80%,焊缝可实现180°无裂纹、无断裂的正向弯曲。同时,箱体结构也通过了产品的试验验证。该硫酸阳极化机箱搅拌摩擦焊的焊接结构设计及工艺,对此类产品的制造具有一定的指导意义。     

Effect of process parameters on friction stir welding of aluminum alloy 2219-T87

In this work, successful friction stir welding of aluminum alloy 2219 using an adapted milling machine is reported. The downward or forging force was found to be dependent upon shoulder diameter and rotational speed whereas longitudinal or welding force on welding speed and pin diameter. Tensile strength of welds was significantly affected by welding speed and shoulder diameter whereas welding speed strongly affected percentage elongation. Metallographic studies revealed fine equiaxed grains in weld nugget and microstructural changes in thermo-mechanically affected zone were found to be the result of combined and interactive influences of frictional heat and deformation. A maximum joining efficiency of 75% was obtained for welds with reasonably good percentage elongation. TEM studies indicated coarsening and/or dissolving of precipitates in nugget. For the gas metal arc weld, SEM investigations revealed segregation of copper at grain boundaries in partially melted zone.     

焊接工艺参数对5383铝合金搅拌摩擦焊接头耐腐蚀性的影响

在制备不同焊接工艺条件下的5383铝合金搅拌摩擦焊接头的基础上,利用扫描电镜与能谱分析方法研究搅拌摩擦焊接头典型区域的宏观形貌特征与显微形貌特征,得到焊接速度、搅拌头转速及搅拌头压力等焊接工艺参数对接头耐腐蚀性的影响规律,结果表明:在特定的焊接工艺条件下,焊缝区域会产生S线。S线是接头腐蚀最严重的区域,其原因是由Mg元素偏聚、大量微孔的聚集与锰铁化合物的形成等三方面因素造成的;除S线及其附近区域外的焊缝其他区域的耐腐蚀性优于母材。同时,分析三种因素导致焊接接头耐腐蚀性降低的原理,阐述不同焊接工艺参数对5383铝合金搅拌摩擦时接头中S线形成的影响,提出利用减少焊接速度、增加搅拌头转速与提高搅拌头压力的方法来改善5383铝合金搅拌摩擦焊接头的耐腐蚀性。     

Effects of welding speed on microstructures and mechanical properties of AA2219-T6 welded by the reverse dual-rotation friction stir welding

Reverse dual-rotation friction stir welding (RDR-FSW) is a novel FSW technology in which the tool pin and the assisted shoulder rotates reversely, thus it has the capability to obtain appropriate welding conditions through adjusting the rotating tool pin and surrounding assisted shoulder independently. In the present study, a RDR-FSW tool system was designed and successfully applied to weld high strength aluminum alloy 2219-T6, and the effects of welding speed on microstructures and mechanical properties were investigated in detail. At a constant rotation speed of 800 rpm for both the rotating tool pin and the reversely rotating assisted shoulder, defect-free joints were obtained at welding speeds ranging from 50 to 150 mm/min, while a cavity defect appeared at the three-phase confluction on the advancing side when the welding speed increased to 200 mm/min. With increasing of the welding speed, the width of the softened region decreased, but the minimum microhardness value increased gradually. When compared with the joints welded by the conventional FSW, there is only a minor variation of the Vickers hardness across the stirring zone in the joint welded by the RDR-FSW. The maximum tensile strength 328 MPa (73.7 % of the base material) was obtained at the welding speed of 150 mm/min, while the elongation reached its maximum 7.0 % (60.9 % of the base material) at the welding speed of 100 mm/min. All defect-free joints were fractured at the weakest region with the minimum Vickers hardness, while for the joint with cavity defects the fracture occurred at the defect location. The tensile fracture was in the ductile fracture mode.