Friction Stir Welding Of AA6061-T6 Research Articles

Dissimilar Friction Stir Butt Welding of AA6061-T6 and AA6061/SiCp Composite: Microstructural Characteristics, Impact Toughness, Hardness, Strength Under Transverse Impact

Impact response of dissimilar friction stir welded (FSWed) joints between a monolithic alloy and metal matrix composite has not been yet reported and thus requires a detailed investigation. Therefore, an exhaustive research on the microstructure, microhardness, tensile properties, fracture toughness and failure response under transverse impact of the FSWed AA6061-T6/AA6061 + SiCp joint was conducted within the study. The plates of size 300 × 120 × 3.2 mm3 were friction stir butt welded using a tool rotational speed of 1000 rpm, welding speed of 80 mm/min, tilt angle of 1° and a penetration depth of 0.2 mm into the upper surface of the workpieces. The obtained results indicated that there is no defect in the weld zone of the FSWed dissimilar joint. Microhardness distribution across the mid-thickness of the joint demonstrated superior Vickers hardness within the nugget zone compared to that of AA6061-T6. In addition, tensile rupture took place away from the weld region on the advancing side in the joint for all transverse tensile test specimens. It was also demonstrated that the FSW process resulted in a significant enhancement in fracture toughness compared to those of the base materials. Furthermore, weld nugget of the joint withstood the applied transverse impact energies ranging between 2.5 and 7.5 J.

Effect of Pre-Strain Rolling on Annealing Behavior of Friction-Stir Welded AA6061-T6 Aluminum Alloy

In this work, the effect of pre-strain cold rolling on thermal stability of friction-stir welded AA6061-T6 alloy was studied. The pre-strain rolling was found to be very effective in suppression of abnormal grain growth during standard post-weld T6 heat treatment. It was also shown that the efficiency of this approach essentially depends on rolling path and the rolling along welding direction was the most effective rolling schedule.

Multi-Objective Optimization of Friction Stir Welding Process Parameters of AA6061-T6 and AA7075-T6 Using a Biogeography Based Optimization Algorithm.

The development of Friction Stir Welding (FSW) has provided an alternative approach for producing high-quality welds, in a fast and reliable manner. This study focuses on the mechanical properties of the dissimilar friction stir welding of AA6061-T6 and AA7075-T6 aluminum alloys. The FSW process parameters such as tool rotational speed, tool traverse speed, tilt angle, and tool offset influence the mechanical properties of the friction stir welded joints significantly. A mathematical regression model is developed to determine the empirical relationship between the FSW process parameters and mechanical properties, and the results are validated. In order to obtain the optimal values of process parameters that simultaneously optimize the ultimate tensile strength, elongation, and minimum hardness in the heat affected zone (HAZ), a metaheuristic, multi objective algorithm based on biogeography based optimization is proposed. The Pareto optimal frontiers for triple and dual objective functions are obtained and the best optimal solution is selected through using two different decision making techniques, technique for order of preference by similarity to ideal solution (TOPSIS) and Shannon’s entropy.

Predicting the tensile strength, impact toughness, and hardness of friction stir-welded AA6061-T6 using response surface methodology

In this research, an attempt has been made to develop mathematical models for predicting mechanical properties including ultimate tensile strength, impact toughness, and hardness of the friction stir-welded AA6061-T6 joints at 95 % confidence level. Response surface methodology with central composite design having four parameters and five levels has been used. The four parameters considered were tool pin profile, rotational speed, welding speed, and tool tilt angle. Three confirmation tests were performed to validate the empirical relations. In addition, the influence of the process parameters on ultimate tensile strength, impact toughness, and hardness were investigated. The results indicated that tool pin profile is the most significant parameter in terms of mechanical properties; tool with simple cylindrical pin profile produced weld with high ultimate tensile strength, impact toughness, and hardness. In addition to tool pin profile, rotational speed was more significant compared to welding speed for ultimate tensile strength and impact toughness, whereas welding speed showed dominancy over rotational speed in case of hardness. Optimum conditions of process parameters have been found at which tensile strength of 92 %, impact toughness of 87 %, and hardness of 95 % was achieved in comparison to the base metal. This research will contribute to expand the scientific foundation of friction stir welding of aluminum alloys with emphasis on AA6061-T6. The results will aid the practitioners to develop a clear understanding of the influence of process parameters on mechanical properties and will allow the selection of best combinations of parameters to achieve desired mechanical properties.

Prediction of fatigue life of welding tool in friction stir welding of AA6061-T6

Computational fluid dynamics model is proposed for the calculation of tool forces in friction stir welding of AA6061-T6. Then, a finite element model is established to calculate the fatigue stress of the welding tool. Damage accumulation method and KBM multiaxial fatigue formulation are used to predict the fatigue life of the welding tool. Results indicate that the fatigue stresses on the tool pin are in tension at the front side and in compression at the rear side. Fatigue life of the welding tool can be increased with the increase of the rotation speed and can be decreased with the increase of the transverse speed. Both the increase of the shoulder diameter and the pin diameter can lead to the increase of the fatigue life of the welding tool.

Effects of Heat Transfer on Microhardness and Microstructure of Friction Stir Welded AA 6061 Aluminum Alloy

In this research work, the effects of heat transfer on microhardness, microstructures of friction stir welded AA 6061-T6 Aluminum alloy butt joints advancing side and retreating side are analyzed. A three dimensional finite element model is developed to study the thermal history in the butt welding of AA 6061 aluminum alloy using ANSYS package. Solid 70 elements are used to develop the model and a moving co-ordinate has been introduced to model the three-dimensional heat transfer process because it reduces the difficulty of modeling the moving tool. In this model, the main parameter considered is the heat input from the tool shoulder and tool pin. As a result, the temperature distributions of the weld at a welding speed of 1.25mm/sec were obtained.

Effect of tool rotational speed on residual stress, microstructure, and tensile properties of friction stir welded 6061-T6 aluminum alloy thick plate

In the present study, the effect of tool rotational speed on residual stress, microstructure, and tensile properties of friction stir welded AA 6061-T6 was investigated. AA 6061-T6 plates with a thickness of 16 mm were friction stir welded using three different tool rotational speeds of 500, 700, and 900 rpm and a constant welding speed of 120 mm/min. The results indicate that the longitudinal residual stress distribution is an M-shaped distribution in the transverse direction; in weld region, the tensile longitudinal stress in the advancing side is larger than that in the retreating side. With increasing rotation speed, the values of the tensile longitudinal residual stresses increased slightly, the peak tensile longitudinal stresses appear at the edge of the shoulder in the AS of the joints, and the maximum value of tensile longitudinal residual stress was 153 MPa with the rotation speed of 900 rpm which reaches up to 55 % of the yield strength of AA 6061-T6. Meanwhile, only the appearance of welded joint with 700 rpm is smooth. The grain size in WNZ grows up with increasing the rotation speed. The microhardness variation is determined by microstructure evolution, and the average microhardness decreases with increasing the rotation speed. The welded joint with the rotation speed of 700 rpm performs the maximum tensile strength of 236 MPa which is 76 % of the base material strength.

Numerical studies of effect of tool sizes and pin shapes on friction stir welding of AA2024-T3 alloy

Coupled thermo-mechanical model was used to investigate the effects of the pin diameter, the shoulder diameter and the in conical angle on the heat generations, the material deformations and the energy histories in friction stir welding (FSW) of AA2024-T3 alloy. Results indicate that the shoulder-plate contact area takes more important contribution to the heat generation than the pin-plate contact area. The increase of the shoulder diameter or the decrease of the pin diameter can lead to the increase of the welding temperature in FSW, but the change of shoulder size is more important. Compared to the cases in FSW of AA6061-T6, the input power is obviously increased in FSW of AA2024-T3 and the ratio of the plastic dissipation to the friction dissipation becomes decreased.

A study on natural aging behavior and mechanical properties of friction stir-welded AA6061-T6 plates

Mechanical properties, microstructural events, residual stresses, and aging behavior of friction stir-welded AA6061-T6 were investigated in this work. Microstructural and mechanical characterizations of the friction stir-welded joints in as-welded and post-welded conditions were made by means of optical metallography, transmission electron microscopy, X-ray diffraction for determination of residual stresses, tensile testing, and hardness measurements. It was found that weld strength and hardness variations after welding are mainly dependent on the imposed heat input per unit length. Besides, the kinetics of natural aging in the welded samples was found to be noticeable within the first 14 days, and its effect decreases considerably in longer aging durations. The residual stress measurements show that subsequent natural aging leads to considerable relaxation of residual stress of about 22 MPa, while this effect is particularly significant in the stir zone and the thermomechanically affected zone.

Artifitial Aging Time Effect on Corrosion Resistance for Friction Stir Welded AA6061 T6

This work aims to study the effect of heat treatment on the corrosion resistance of friction stir welded joint of AA 6061 T6.Friction stir welding process carried out using CNC milling machine with a tool of rotational speed (1000 rpm) and welding speed of (20mm/min) to obtain butt joint welding of sheets which prepared from AA 6061 T6 in the dimensions of (100 mm x 70mm x 6mm ).After obtaining the welded joints many corrosion specimens were prepared in dimensions of (15*15*2) mm according to ASTM G 71-31 , specimens subjected to solution heat treatment at 500ºC for half an hour then water quenched, this process followed by artificial ageing at 190ºC for 2, 4, and 6hrs.All specimens subjected to hardness test and microstructure examination to show the effect of the heat treatment on the mechanical properties and microstructure.Corrosion behavior of the specimens were studied before and after heat treatment by using potentiostatic method in sea water at 3.5%NaCl and temperature of 30ºC, then corrosion rate was calculated by using Tafel equation.The obtained results show that artificial aging treatment contributed in increasing the corrosion resistance of weld because of presence of precipitate phases occurring in the microstructures of the welding zone but corrosion resistance decreased as increasing ageing time because of the increasing of the precipitating elements. It was found that artificial ageing for 2 hours gives the best corrosion resistance.

INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDED AA 6061-T6 ALLOY AND MG AZ31B ALLOY

The present study investigates the influence of tool pin profiles on microstructure and mechanical properties of friction stir welded AA 6061-T6 Alloy was studied. An attempt is made here to review the fundamental principle of this process its tensile strength and examination of its metallurgical consequences. An improved milling machine is fabricated for performing friction stir welding and its effectiveness in joining Al 6061-T6 Alloy plates is demonstrated in the current work. The FSW Process has proved to be very efficient and has immense potential for future application. Present investigation is to find out the optimum mechanical properties of friction stir welding of Al 6061-T6 alloy &Mg AZ31B alloy. In this present study an attempt has been made to study the effect of tool rotational speed, traversing speed and tool pin profiles (Taper Thread profile) on FSW zone transformation in Al and Mg alloys. For three different tools, rotational speeds, three different traversing speeds, and three different tool D/d ratios, one tool pin profile have been used to fabricate the joints. The formation of FSW of Al 6061 of fusion zone has been evaluated and correlated with base metal. Tensile properties, toughness and microstructure of the joint were evaluated and correlated as received Al 6061-T6 & Mg AZ31B alloys. The joints fabricated using rotational speed of 1120rpm, a welding speed of 40 mm/min, taper thread pin profile, tool shoulder diameter of 18 mm, (D/d)=3.0 showed higher tensile properties compared to other joints.

Evolution of microstructures and mechanical properties in similar and dissimilar friction stir welding of AA5086 and AA6061

In this work, thermo-mechanical behavior and microstructural evolution in similar and dissimilar friction stir welding of AA6061-T6 and AA5086-O have been investigated. Firstly, the thermo-mechanical behaviors of materials during similar and dissimilar FSW operations have been predicted using three-dimensional finite element software, ABAQUS, then, the mechanical properties and the developed microstructures within the welded samples have been studied with the aid of experimental observations and model predictions. It is found that different strengthening mechanisms in AA5086 and AA6061 result in complex behaviors in hardness of the welded cross section where the hardness variation in similar AA5086-O joints mainly depends on recrystallization and generation of fine grains in weld nugget, however, the hardness variations in the weld zone of AA6061/AA6061 and AA6061/AA5086 joints are affected by subsequent aging phenomenon. Also, both experimental and predicted data illustrate that the peak temperature in FSW of AA6061/AA6061 is the highest compared to the other joints employing the same welding parameters.

Thermo-mechanical and microstructural issues in dissimilar friction stir welding of AA5086–AA6061

In this research, thermo-mechanical behavior and microstructural events in dissimilar friction stir welding of AA6061-T6 and AA5086-O have been evaluated. The thermo-mechanical responses of materials during the process have been predicted employing a three-dimensional model together with a finite element software, ABAQUS. Then, mechanical properties and microstructures of the weld zone were studied with the aid of experimental observations and model predictions. It is found that the mixing of material in the weld nugget is performed more efficiently when AA5086 is in the advancing side and also the temperature field is distributed asymmetrically resulting in larger thermally affected region in the AA6061 side. Besides, the microstructural studies shows that the microstructures of stirred zone consist of fine equiaxed grains where finer grains are produced in AA6061 side compared to AA5086 side.

Establishing empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints

AA 6061-T6 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high specific strength and good corrosion resistance. Compared with the fusion welding processes that are routinely used for joining structural aluminium alloys, friction stir welding (FSW) process is an emerging solid state joining process in which the material welded does not melt and recast. Joint strength is influenced by the grain size and tensile strength of the weld nugget region. Hence, an attempt was made to develop empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints. The empirical relationships are developed by response surface methodology (RSM) incorporating FSW tool and process parameters. A linear regression relationship was also established between grain size and tensile strength of the weld nugget of FSW joints.