Experimental and numerical investigation on under-water friction stir welding of armour grade AA2519-T87 aluminium alloy

Friction stir welding(FSW) is a promising welding process that can join age hardenable aluminium alloys with high joint efficiency. However,the thermal cycles experienced by the material to be joined during FSW resulted in the deterioration of mechanical properties due to the coarsening and dissolution of strengthening precipitates in the thermo-mechanical affected zone(TMAZ) and heat affected zone(HAZ). Under water friction stir welding(UWFSW) is a variant of FSW process which can maintain low heat input as well as constant heat input along the weld line. The heat conduction and dissipation during UWFSW controls the width of TMAZ and HAZ and also improves the joint properties. In this investigation, an attempt has been made to evaluate the mechanical properties and microstructural characteristics of AA2519-T87 aluminium alloy joints made by FSW and UWFSW processes. Finite element analysis has been used to estimate the temperature distribution and width of TMAZ region in both the joints and the results have been compared with experimental results and subsequently correlated with mechanical properties.? 2016 China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.

Experimental investigation on friction stir welding of 2A12 aluminium alloys

Friction stir welding experiments were conducted to study the effects of the process parameters on the weld quality of 2A12 aluminium alloys. Through appropriate selection of the shoulder press amount （axial force）, tool rotation speed and welding speed, good joints were obtained for the test pieces with thickness of 6 ram. The microstructures in weld nugget zone, thermo-mechanical affected zone and heat-affected zone were analyzed. It is found that the ratio of the tool rotation speed to the welding speed should be optimized for a suitable shoulder press amount.

Visualization and simulation of plastic material flow in friction stir welding of 2024 aluminium alloy plates

Thin copper sheets as marker material were embedded into weld path of 2024 aluminium alloy plates and their final position after friction stir welding was examined by metallographic techniques. Referring to the visualized material flow patterns, a three-dimensional model was developed to conduct the numerical simulation of the temperature profile and plastic material flow in friction stir welding. The calculated velocity contour of plastic flow in close proximity of the tool is generally consistent with the visualized results. As the tool rotation speed increases at a constant tool travel speed, the material flow near the pin gets stronger. The predicted shape and size of the weld nugget zone match with the experimentally measured ones.

Developing friction stir welding window for AA2219 aluminium alloy

A friction stir welding window was developed for effective joining of AA2219 aluminium alloy. Joints were fabricated using different combination of process parameters such as rotational speed and welding speed. Based on macrostructural analysis, the friction stir welding window was constructed. The strength values of joints at different regions of friction stir welding window were analyzed using tensile properties, microstructural studies, and the fracture location of joints was correlated with the lowest hardness distribution profiles. These windows will act as reference maps for selecting appropriate friction stir welding process parameters to get good quality welds of AA2219 aluminium alloys.

Mechanism of corrosion fatigue fracture of friction stir welding joints of 7075 aluminium alloy in 3.5% NaCl solution

The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zone(NZ)and thermo-mechanical affected zone(TMAZ). Multiple crack sources are developed at the same time, and they merge into large cracks along the boundary line of NZ and TMAZ during the propagation stage. Furthermore, a mutual reinforcement coupling always exists between corrosion and cyclic loading during the initiation and propagation of corrosion fatigue crack. It is necessary to consider the effect of welding residual stress for understanding the mechanism of corrosion fatigue fracture of FSW joints.

Process parameters optimization for friction stir welding of RDE-40 aluminium alloy using Taguchi technique

Taguchi approach was applied to determine the most influential control factors which will yield better tensile strength of the joints of friction stir welded RDE-40 aluminium alloy. In order to evaluate the effect of process parameters such as tool rotational speed, traverse speed and axial force on tensile strength of friction stir welded RDE-40 aluminium alloy, Taguchi parametric design and optimization approach was used. Through the Taguchi parametric design approach, the optimum levels of process parameters were determined. The results indicate that the rotational speed, welding speed and axial force are the significant parameters in deciding the tensile strength of the joint. The predicted optimal value of tensile strength of friction stir welded RDE-40 aluminium alloy is 303 MPa. The results were confirmed by further experiments.

Effect of Process Parameters on Tensile Strength of Friction Stir Welded Cast LM6 Aluminium Alloy Joints

This paper reports the effect of friction stir welding （FSW） process parameters on tensile strength of cast LM6 aluminium alloy. Joints were made by using different combinations of tool rotation speed, welding speed and axial force each at four levels. The quality of weld zone was investigated using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a rotational speed of 900 r/min, a welding speed of 75 mm/min and an axial force of 3 kN showed superior tensile strength compared with other joints. The tensile strength and microhardness of the welded joints for the optimum conditions were 166 MPa and 64.8 Hv respectively.

Corrosion performance of friction stir welded AA2024 aluminium alloy under salt fog conditions

Aluminium alloy（AA） 2024 is an important engineering material due to its widespread use in the aerospace industry. However, it is very prone to corrosion attack in chloride containing media. In the present investigation, AA2024 aluminium alloy rolled plates of 5 mm in thickness were friction stir welded. Corrosion performances of the specimens were evaluated by conducting salt fog tests in Na Cl solution at different p H values, chloride ion concentrations and spraying time. In addition, an empirical relationship was established to predict the corrosion rate of friction stir welds of AA2024 aluminium alloy. A central composite rotatable design including three factors and five levels was used to minimize the number of experiments. Response surface methodology（RSM） was used to develop the relationship. The corrosion rate decreased under neutral p H conditions. The corrosion rate increased in acidic and basic conditions. It was also found that the corrosion rate decreased with the increase of spraying time, but the corrosion tended to be uniform with the increment of time and with the increase in the chloride ion concentration, and the corrosion rate increased in the salt spray corrosion test.

Effect of process parameters on tensile strength of friction stir welded cast A356 aluminium alloy joints

A356 is a high strength aluminium-silicon cast alloy used in food,chemical,marine,electrical and automotive industries.Fusion welding of this cast alloy will lead to many problems such as porosity,micro-fissuring,and hot cracking.However,friction stir welding（FSW） can be used to weld this cast alloy without above mentioned defects.An attempt was made to study the effect of FSW process parameters on the tensile strength of cast A356 aluminium alloy.Joints were made using different combinations of tool rotation speed,welding speed and axial force.The quality of weld zone was analyzed by macrostructure and microstructure analyses.Tensile strengths of the joints were evaluated and correlated with the weld zone hardness and microstructure.The joint fabricated using a rotational speed of 1000 r/min,a welding speed of 75 mm/min and an axial force of 5 kN showed a higher tensile strength compared to the other joints.

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of Friction Stir Welded SSM7075 Aluminium Alloy

7XXX series aluminium alloys generally present low weldability by fusion welding methods because of the sensitivity to weld solidification cracking, vaporization of strengthening alloys and other defects in the fusion zone. Friction stir welding（FSW） can be deployed successfully with aluminium alloys. We presented the effect of post-weld heat treatment（PWHT） on the microstructure and mechanical properties of SSM7075 joints. Semi solid plates were butt-welded by FSW at a rotation speed of 1110 r/min, welding speeds of 70 and 110 mm/min. Solution treatment, artificial aging, and T6（solution treatment and artificial aging combined） were applied to the welded joints, each with three samples. It was found that the T6 joints at the speed of 70 mm/min yielded the highest tensile strength of 459.23 MPa. This condition best enhanced the mechanical properties of FSW SSM7075 aluminium alloy joints.

Fatigue crack growth behaviour of friction stir welded AA7075-T651 aluminium alloy joints

The aim of the present work is to evaluate the fatigue crack growth behaviour of 12 mm thick AA 7075-T651 aluminium alloy plates joined by FSW. Fatigue crack growth test was carried out on center cracked tensile (CCT) specimens extracted from the FSW joints and unwelded parent metal. Transverse tensile properties of the unwelded parent metal and welded joints were evaluated. Microstructures of the welded joints were analyzed using optical microscopy and transmission electron microscopy. The scanning electron microscope was used to characterize the fracture surfaces. It was found that the ΔKcr of the welded joint is reduced by 10×10-3 MPa·m1/2 in comparison with the unwelded parent metal. Hence, the fatigue life of the friction stir welded AA 7075-T651aluminium alloy joints is appreciably lower than that of the unwelded parent metal, which is attributed to the dissolution of precipitates in the weld region during friction stir welding.

Microstructure and tensile properties of friction stir welded dissimilar AA6061-AA5086 aluminium alloy joints

The fusion welding of dissimilar heat treatable and non-heat treatable aluminium alloy faced many problems related to solidification. The difficulties can be overcome to achieve the combined beneficial properties of both aluminium alloys using friction stir welding(FSW). The microstructural features and tensile properties of friction stir welded(FSW) similar and dissimilar joints made of AA6061 and AA5086 aluminium alloys were investigated. The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscopy. Microhardness was measured at various zones of the welded joints. The tensile properties of the joints were evaluated and correlated with the microstructural features and microhardness values. The dissimilar joint exhibits a maximum hardness of HV 115 and a joint efficiency of 56%. This was attributed to the defect free stir zone formation and grain size strengthening.

Mechanical and metallurgical properties of friction stir welded dissimilar joints of AZ91 magnesium alloy and AA 6082-T6 aluminium alloy

In the present research work,AZ91 magnesium alloy and AA6082-T6 aluminium alloy were joined by friction stir welding process.The comparison of microstructure and mechanical properties between different joints by varying the different materials on advance and retreating sides were mainly studied.Four different welds have been prepared to find the material mixing between the similar and dissimilar joints.The joint interfaces of the welds have been investigated by employing an optical microscope and scanning electron microscope.When Mg was placed on advancing side(AS),more aluminium content was soluble in nugget zone than the case where Mg was placed on the retreating side(RS).Thin intermetallic layer in the joint interface of Mg/Al and thick intermetallic layer with poor adhesion of the aluminium and magnesium have been observed in the dissimilar joints varying the sides.The highest UTS of 172.3 MPa was found for Mg-Al when Mg was placed on AS and lower UTS of 156.25 MPa was obtained when Mg was placed on RS.Hardness of 86 Hv and 89 Hv were observed in the Stir zone for the dissimilar AZ91 Mg alloy and AA6082-T6 Al alloy when AZ91Mg alloy was placed on the AS and on the RS respectively.Fractography was also carried out to find the mode of failure.

Design of experiment study on hardness variations in friction stir welding of AM60 Mg alloy

Identification of process parameters,their effects and contributions to the outcomes of the system using experimental approach could be a daunting,time consuming,and costly course.Using proper statistical methods,i.e.,Taguchi method,could significantly reduce the number of required experiments and statistical significance of the parameter can be identified.Friction stir welding is one of those welding techniques with many parameters which have different effects on the quality of the welds.In friction stir welding the tool rotational speed(RPM)and transverse speed(mm/min)influence the strength(i.e.,hardness distribution)of the stirred zone.In this study,these two factors are investigated to determine the effect they will have on the hardness in the stirred zone of the friction stir welds and how the two factors are related to one another for as-cast magnesium alloy AM60 with nominal chemical composition of Mg-(5.5-6.5)Al-(0.24-0.6)Mn-0.22Zn-0.1Si.Experimental data was taken at three different tool rotational speeds and three different transverse speeds.The data obtained was then analyzed using a 32 factorial design to find the contribution of these parameters.It was determined that both tool rotational speed and transverse speed possess significant effects on the stir zone hardness.Also,the interactions between the two factors were statistically assessed.

Effect of welding processes on AA2219 aluminium alloy joint properties

AA2219 aluminium alloy square butt joints without filler metal addition were fabricated using gas tungsten arc welding （GTAW）, electron beam welding （EBW） and friction stir welding （FSW） processes. The effects of three welding processes on the tensile, fatigue and corrosion behaviour were studied. Microstructure analysis was carried out using optical and electron microscopes. The results show that the FSW joints exhibit superior tensile and fatigue properties compared to EBW and GTAW joints. It is also found that the friction stir welds show lower corrosion resistance than EB and GTA welds. This is mainly due to the presence of finer grains and uniform distribution of strengthening precipitates in the weld metal of FSW joints.

Optimizing the micro-arc oxidation (MAO) parameters to attain coatings with minimum porosity and maximum hardness on the friction stir welded AA6061 aluminium alloy welds

Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relationships were derived to evaluate the MAO coating properties(porosity and hardness) by incorporating very important MAO parameters(current density, inter-electrode distance and oxidation time). MAO parameters were also optimized to achieve coatings with minimum porosity and maximum hardness. Further, the effect of MAO parameters on coating characteristics was analysed. From the results, it is found that the current density has greater influence on the responses than the other two parameters.

Effect of tool pin profile on microstructure and tensile properties of friction stir welded dissimilar AA 6061e AA 5086 aluminium alloy joints

Joints between two different grades of aluminium alloys are need of the hour in many light weight military structures.In this investigation,an attempt has been made to join the heat treatable(AA 6061) and non-heat treatable(AA 5086) aluminium alloys by friction stir welding(FSW)process using three different tool pin profiles like straight cylindrical,taper cylindrical and threaded cylindrical.The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscope.The tensile properties and microhardness were evaluated for the welded joint.From this investigation it is founded that the use of threaded pin profile of tool contributes to better flow of materials between two alloys and the generation of defect free stir zone.It also resulted in higher hardness values of 83 HV in the stir zone and higher tensile strength of 169 MPa compared to other two profiles.The increase in hardness is attributed to the formation of fine grains and intermetallics in the stir zone,and in addition,the reduced size of weaker regions,such as TMAZ and HAZ regions,results in higher tensile properties.

Comparison of RSM with ANN in predicting tensile strength of friction stir welded AA7039 aluminium alloy joints

磨擦搅动(FSW ) 焊接是一种创新稳固的州的加入技术并且在太空，栏杆，为加入铝的汽车、海洋的工业，镁，锌和铜被采用了合金。FSW 过程参数象工具那样旋转速度，焊接速度，轴的力量，在决定焊接质量起一个主要作用。二个方法，反应表面方法论和人工的神经网络被用来预言磨擦的张力的强度搅动焊接 AA7039 铝合金。实验基于三个因素被进行，三水平、中央的合成的脸与完整的复制技术集中了设计，并且数学模型被开发。敏感分析被执行识别批评参数。通过反应表面方法论获得的结果与通过人工的神经网络的那些相比。

Evolution of microstructures and intermetallic compounds at bonding interface in friction stir welding of dissimilar Al/Mg alloys with/without ultrasonic assistance

Complete understanding of the evolution behaviors of the microstructures and intermetallic compounds(IMCs)along the interface materials flow path in friction stir welding(FSW)of dissimilar Al to Mg alloys is of great significance.In this study,conventional FSW and ultrasonic vibration enhanced FSW(UVeFSW)experiments of Al/Mg alloys were performed,and the instantaneous evolution features of the interface materials around the tool were"frozen"by using the"sudden stop"and simultaneous cooling techniques.The microstructures and IMCs formation at different locations around the exit hole were observed and characterized by scanning electron microscope,energy dispersive spectrometer and transmission elec-tron microscope.It was found that before the materials started to deposit near the back of the tool,“IMC+Mg+IMC+Al”multilayer microstructure and simple IMC layer with(β+γ)sequentially emerged on the Al/Mg interface.With the application of ultrasonic vibration,the multi-layered interface structure only appeared at the middle stage of materials flow around the pin,and ultrasonic vibration just began to play a suppression role on the growth of two sub-layers IMC at a position where the materials deposit.With assistance of ultrasonic vibration in UVeFSW,the tool drove a larger volume of Mg alloy to move toward the retreating side,and the final IMCs thickness was thinner than that in FSW.

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium-AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption,weightreduction and emission reduction.However,joining of aluminium(Al)alloys with magnesium(Mg)alloys by fusion welding processis very complicated.Friction stir welding(FSW)is a feasible method to join these two dissimilar alloys.Mixing these two metalstogether in stir zone(SZ)leads to poor corrosion resistance.In this investigation,an attempt has been made to understand thecorrosion resistance of SZ of FSWed dissimilar joints of AA6061Al alloy and AZ31B Mg alloy.Potentiodynamic polarization testwas conducted by varying chloride ion concentration,pH value of the NaCl solution and exposure time.The corroded surfaces wereanalyzed using optical microscopy,scanning electron microscopy and XRD techniques.Of these three factors investigated,exposuretime is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints ofAl/Mg alloys.