Fundamental study on electron beam weld sections and strengths using AA6061-T6 aluminum alloy plate

This study was carried out to establish an electron beam welding process for a nuclear fuel plate assembly fabrication. A preliminary investigation for plate fuel fabrication was conducted with a consideration of weld performance using AA6061-T6 aluminum alloy made by the electron beam welding process. The optimum welding parameters for the fuel plate assembly were obtained in terms of the accelerating voltage, beam current and welding time. The soundness of the weld region between the side plate and the end fitting for the fuel plate assembly was proven by the intact of the weld metal on the fractured surfaces. The integrity of the welds by the electron beam welding process was also confirmed by the results of the tensile test, an examination of the cross sections and the fracture surfaces of the welded specimens.     

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.     

Experimental investigation of weld characteristics on submerged friction stir welded 6061-T6 aluminum alloy

Journal of Mechanical Science and Technology - Mechanical properties such as fatigue life, corrosion resistance, brittle fracture, hardness and dimensional stability mainly depend on the residual...     

Optimization of weld characteristics of friction welded AA 6061-AA 6351 joints using grey-principal component analysis (G-PCA)

Friction welding is a solid state joining process in which the quality of welded joint is influenced by the input parameter setting. The objective of the present study is to conduct experimental investigation of the bond strength and hardness of the friction welded joints involving AA 6061 and AA 6351 alloys by conducting experiments designed by Taguchi’s L⁹ orthogonal matrix array. A systematic approach becomes essential to find the optimal setting of friction welding parameters. Hence a new approach named grey-principal component analysis (G-PCA) is presented in which the principal component analysis (PCA) is used to generate weights for the grey relational coefficients obtained in the grey relational analysis (GRA). The results of the confirmation experiment conducted with the optimal setting predicted by the G-PCA have shown improvements in the performance characteristics. Hence G-PCA can be used for experimental welding optimization.     

Application of QFA coupled with CFD analysis to predict the hardness of T6 heat treated Al6061 cylinder

QFA (quench factor analysis) method is widely used to predict the mechanical properties such as hardness and strength according to temperature of quenched material that has to be determined by experimental heat treatment. But, QFA coupled with CFD (computational fluid dynamics) analysis of this study can predict the mechanical properties without the experiment of heat treatment except the experiment to determine the material constants of QFA. First of all, Jominy test and FPS (flexible polyhedron search) are performed to determine the material constants of QFA. The CFD analysis is applied to predict the cooling temperature of Al6061 cylinder cooled by water of 25°C during quenching of solid solution heat treatment. Hardnesses of T6 heat treated Al6061 cylinder is predicted by the QFA coupled with CFD analysis without experiment of heat treatment and then the predicted hardnesses are compared with experimentally measured hardnesses according to positions of cylinder. The predicted hardnesses of cylinder are in good agreement with the measured ones within a maximum error of 8.45%.     

Effect of pinless tool shoulder diameter on dieless friction stir extrusion joining of AA 5052-H32 and AA 6061-T6 aluminum alloy sheets

Journal of Mechanical Science and Technology - A new spot joining process called dieless friction stir extrusion is proposed, in which simultaneous mechanical interlocking (collar formation) and...     

A study to estimate the tensile strength of friction stir welded AA 5059 aluminium alloy joints

The influence of strain rate on the frictional behaviour of AA7075 aluminium alloy, in the O-annealed temper state, was studied. Attention was focused on the evaluation of the mechanisms affecting friction at high strain rate. To this purpose, axisymmetric and ring compression tests were carried out using the split Hopkinson tension-compression bar in the direct version. The flow curves were investigated in a wide range of strain rates using cylindrical specimens characterised by different slenderness ratios. The results of the axisymmetric compression tests showed an appreciable strain rate sensitivity of the deforming material with a marked increase in flow stress with strain rate in the dynamic loading condition. As far as the ring compression tests are concerned, different strain rates were obtained using hollow cylinders with different initial sizes. The analysis of the results showed that strain rate affects the variation of the inner ring diameter, irrespective of the height reduction and frictional condition. Axysimmetric and ring compression tests were also performed under the quasi-static loading condition and the experimental results did not show any appreciable effect of strain rate on flow curves and frictional behaviour. Finally, the different frictional behaviour between the quasi-static and dynamic loading conditions was attributed both to the reduction in the lubricant film thickness and change in the viscous actions at the specimen-tool interface.     

A fuzzy logic based model to predict surface hardness of thin film TiN coating on aerospace AL7075-T6 alloy

Aerospace applications and energy-saving strategies in general raised the interest and study in the field of lightweight materials, especially on aluminum alloys. Aluminum alloy itself does not have appropriate wear resistance. Therefore, improvement of surface properties is required in practical applications, especially when aluminum is in contact with other parts. In this work, first titanium nitride (TiN) is coated on aerospace Al7075-T6 in different conditions using PVD magnetron sputtering technique, and the surface hardness of TiN-coated specimens is measured using a micro hardness machine. Second, a fuzzy logic model is offered to predict the surface hardness of TiN coating on AL7075-T6 with respect to changes in input process parameters, direct current (DC) power, DC bias voltage, and nitrogen flow rate. Four membership functions are allocated to be connected with each input of the model. The predicted results achieved via fuzzy logic model are compared to the experimental result. The result demonstrated settlement between the fuzzy model and experimental results with 96.142 % accuracy. The hardness of titanium nitride-coated specimens is increased significantly up to 720 HV, while the hardness of uncoated specimens was 170 HV.     

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.     

Effect of weld parameters on mechanical properties and tensile behavior of tungsten inert gas welded AW6082-T6 aluminium alloy

The effect of different welding parameters on the mechanical properties and tensile behavior of tungsten inert gas (TIG) welded joints was analyzed. Four different groove angles were chosen, 60°, 70°, 80° and 90°, to ascertain the tendency of microstructure formation and quality of the weld. Mechanical properties were assessed in the terms of Vickers HV1 hardness. Microanalysis of test samples produced using different current 165 A, 180 A, 200 A with same groove angle of 90° was done in fusion, partially melted, and heat affected zone; all the images showed good penetration and clear transition from one to following zone. The transverse tensile tests were accomplished on the welded joints to evaluate influence of welding parameters and groove geometry to the joint tensile strength and its behavior during exploitation. It was verified that the tensile strength of the welds is closely related to the welding parameters. The chosen 180 A welding current ensured highest tensile strength of test samples; the same as proper selection of groove angle (90°) provides good fusion and high quality of major welds. The results revealed that the weld penetration depends on welding current.

     

Wear and friction of 6061-T6 aluminum alloy treated by laser shock processing

Laser shock processing (LSP) is becoming an important surface treatment to induce a compressive residual stress field, which improves fatigue and fracture properties of components. In this work, we examine the effect of laser shock processing on the wear and friction behavior of 6061-T6 aluminum alloy. Wear rate and friction coefficient evolution are investigated for different process parameters of LSP. Roll-on-flat tribometer is used with different loading conditions. Hardness and residual stresses are assessed as well. It is observed that wear rate decreases as pulse density increases; this is explained in light of residual stress distribution.     

Particle size effects on the slurry erosion of aluminium alloy (AA 6063)

The effect of particle size on erosion wear of aluminium alloy (AA 6063) has been investigated in a slurry pot tester. Eight different sized quartz particles with mean size varying between 37.5 and 655 μm have been used. The wear specimens are rotated inside the pot at 3 m/s velocity with orientation angle of 30° and 90° in a sand–water mixture of 20% concentration (by weight). It is seen that the erosion wear increases with increase in mean particle size. Two distinct mechanisms are noticed for mean particle size above 200 μm and below this size for the range of parameters under this investigation. It seems that a threshold kinetic energy of impacting particle may exist, which results in change in the wear rate at a particular particle size. The threshold kinetic energy for different operating conditions has been determined and its relation with the change in erosion mechanism is discussed.     

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.     

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.     

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.     

Microstructure analysis of aluminum extrusion: grain size distribution in AA6060, AA6082 and AA7075 alloys

Microstructure and material flow of aluminum alloys have a significant influence on the mechanical properties and surface quality. In extrusion of aluminum billets at high temperatures the microstructure is dependent on the alloy and the forming and temperature history. A prediction of grain size and precipitation is of increasing importance in order to design the process by adjustment of parameters such as punch speed, temperatures, and quenching. To give references for microstructure prediction based on material flow, and with it strain and strain rate history, this paper deals with the microstructure during the extrusion process of AA6060, AA6082, and AA7075 alloys. Billets have been partly extruded to axisymmetric round profiles and the microstructure of the press rests consisting of the billet rests in container and die has been considered. Furthermore, these rests have been analyzed to show the material flow, dynamic and static recrystallization based on macro etchings and visible microstructure under different conditions, e.g. as in the area of high strain rate near the container wall, or in dead zones [1]. To allow an accurate simulation of the extrusion process, punch force and temperature conditions during the tests have been measured and are presented in this paper, too.     

On the FSW of AA2024-T4 and AA7075-T6 T-joints: an industrial case study

The paper presents an artificial neural network-optimization hybrid model to predict and optimize penetration depth of CO₂ LASER-MIG hybrid welding used for 5005 Al–Mg alloy. The input welding parameters are power, focal distance from the work piece surface, torch angle, and the distance between the laser and the welding torch. The model combines single hidden layer back propagation artificial neural networks (ANN) with Bayesian regularization for prediction and quasi-Newton search algorithm for optimization. In this method, training and prediction performance of different ANN architectures are initially tested, and the architecture with the best performance is further used for optimization. Finally, the best ANN architecture is found to show much better prediction capability compared to a regression model developed from the experimental data.