Stir Welded Aluminium Alloy Joints Research Articles

Entire-Process Simulation of Friction Stir Welding — Part 2: Implementation of Neural Networks

To further understand the structure-parameter-property relationships of friction stir welded aluminum alloy joints, a nested neural network was proposed to map the macro- and microstructural response. The uncoupled effect of each primitive parameter on the joint performance was depicted. Reducing heat input and keeping an adequate load-bearing area of the welding nugget zone were proven to be the sufficient and necessary conditions to obtain high load-bearing performance. The entire-process simulation strategy showed great potential for prediction and optimization of the macro- and microstructural response of complex and large components.

Detection of tunnel defects in friction stir welded aluminum alloy joints based on the in-situ force signal

The demand for high quality and effective manufacturing has raised the need for defect identification in friction stir welding. This work aims to identify the tunnel defect inside the welded joint based on the feature of in-situ force signals. First, we measured the traverse force (Fx), lateral force (Fy) and plunge force (Fz) during the welding process and analyzed the variation characteristic of the force signals for the joints with and without tunnel defect. Then, fast Fourier transform was utilized to obtain the frequency components of the force signal for analyzing the cause of the waveform distortion of the welding force, which showed a direct relationship with the occurrence of the tunnel defect in the joint. The combination result of the frequency components indicated that the waveform distortion of Fx and Fy for the defective joint was mainly influenced by the first harmonic and third harmonic. Thus, a defect detection indicator was proposed by calculating the normalization ratio of the amplitudes of the third harmonic and first harmonic. Tshe best accuracy of the indicator from Fx for identifying the tunnel defect reached 96.42%. Furthermore, the simulation results of the FSW process provide a physical understanding of material flow and defect formation indicated by the first harmonic and third harmonic of Fx, which helps explain the high accuracy of the proposed indicator from Fx signal in the detection of tunnel defect.

Effect of tool axis offset and relative position of materials on the performance of dissimilar friction stir welded aluminium alloy joints–an overview

At present most of the manufacturing sectors are looking for high strength lightweight structures with high specific stiffness and good corrosion resistance. In this context, combined use of different types of aluminium alloys are required and warrants efficient joining of the dissimilar alloys. But, efficient joining of dissimilar aluminium alloys by fusion welding techniques is very difficult due to the poor weldability of dissimilar aluminium alloys. It is reported that FSW being a solid state welding technique can avoid all problems associated with fusion welding and is a potential candidate technique for joining difficult to weld materials including dissimilar aluminium alloys. With regard to FSW dissimilar aluminium alloys, the tool axis offset and relative positioning of alloys are also reported to be important. In this article, a comprehensive discussion on the influence of tool axis offset and relative positioning of the materials on the joint performance that reported in the literature is presented. The literature showed that there is uniqueness in the value and sign of the tool axis offset that can result defect free joint with good joint properties. With regard to relative positioning of the materials also, conflicting arguments are reported in the literature.

Utilization of Random Vector Functional Link integrated with Marine Predators Algorithm for tensile behavior prediction of dissimilar friction stir welded aluminum alloy joints

Friction stir welding (FSW) method becomes an effective technique for welding dissimilar alloys such as AA2024 and AA5083 as the conventional fusion welding methods are not very suitable for welding the dissimilar alloysand cause many defects during solidification process. Since the strength of FSWedjoints depends on the process parameters, a new method was used in this study to predict the tensile behavior of friction stir welded AA5083 and AA2024 aluminum alloy joints in terms of tensile elongation (TE) and ultimate tensile strength (UTS). A new metaheuristic algorithm called Marine Predators Algorithm (MPA) has been integrated with Random Vector Functional Link (RVFL) network to improve the prediction accuracy. Rotational speed, welding speed, tool axial force, and pin profile were used as input parameters while UTS and TE works as the corresponding outputs. The MPA-RVFL model was tested and validated,a great agreement was demonstrated between the experimental results and the predicted results indicating that the developed technique is accurate and reliable to predict the tensile behavior of welded aluminum joints.

Fatigue of Friction Stir Welded Aluminum Alloy Joints: A Review

The application fields of friction stir welding technology, such as aerospace and transportation, has high safety requirements and fatigue is the dominant failure mode for weldments. It is of great significance to understand the fatigue properties of friction stir welded joints. This paper provides an overview of the fatigue mechanism, influencing factors, crack growth rate, and fatigue life assessment. It is found that the fatigue performance of friction stir welded joints can be affected by welding process parameters, test environment, stress ratio, residual stress, and weld defect. The optimized process parameters can produce high quality weld and increase the weld fatigue life. Laser peening is an effective post weld treatment to decrease fatigue crack growth rate and improve material fatigue life.

Role of non-consumable tool design on tensile properties of friction stir welded aluminium alloy joints

A solid state welding, like friction stir welding (FSW) is commonly suitable for joining dissimilar aluminium plates. A non-consumable revolving tool was used to induce heat and plastic distortion between abutting surfaces of the plates. This paper, presented the influence of tool revolving speed, axial force and weld transverse speed on tensile and impact strength properties were evaluated for the joint by using destructive test. The FSW has been done at tool revolving speed of 1000, 1100, 1200 rpm, weld speed of 30, 45, 60 mm/min and tool plunge force of 3, 4, 5 kN on dissimilar aluminium alloy AA7075 and AA6063 by two different tool profiles of Triangle and square. Better mixing of both aluminium alloy joints was achieved at lower welding transverse speed of 30 mm/min with high tool revolving speed of 1200 rpm. Also it is found that the use of the triangular profile of the tool gives better mechanical properties. The growth in mechanical properties is attributed to the maturation of fine grain and intermetallic compound in the weld region.

Mathematical Modeling of Process Parameters of Friction Stir Welded Aluminium Alloy Joints Using Central Composite Design

The structural application of aluminium alloy involves welding and joining, which are difficult to weld using conventional welding processes. In 1991 a solid state joining process named Friction Stir Welding was developed and this technique has attracted considerable interest from the aerospace and automotive industries, since it is able to produce defect free joints particularly for light metals i.e aluminum alloy and magnesium alloy. 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 and tool shoulder diameter play a major role in deciding the weld quality. In this research work an attempt has been made to understand the effect of tool rotational speed, welding speed and tool shoulder diameter on friction stir welding of AA6061 aluminium alloy. Statistical tools such as design of experiments, analysis of variance, and regression analysis are used to develop the relationships. The mathematical model has been developed to predict mechanical properties of friction stir welded aluminium alloy joints at the 95% confidence level

Role of non-consumable tool design on tensile properties of friction stir welded aluminium alloy joints

A solid state welding, like friction stir welding (FSW) is commonly suitable for joining dissimilar aluminium plates. A non-consumable revolving tool was used to induce heat and plastic distortion between abutting surfaces of the plates. This paper, presented the influence of tool revolving speed, axial force and weld transverse speed on tensile and impact strength properties were evaluated for the joint by using destructive test. The FSW has been done at tool revolving speed of 1000, 1100, 1200 rpm, weld speed of 30, 45, 60 mm/min and tool plunge force of 3, 4, 5 kN on dissimilar aluminium alloy AA7075 and AA6063 by two different tool profiles of Triangle and square. Better mixing of both aluminium alloy joints was achieved at lower welding transverse speed of 30 mm/min with high tool revolving speed of 1200 rpm. Also it is found that the use of the triangular profile of the tool gives better mechanical properties. The growth in mechanical properties is attributed to the maturation of fine grain and intermetallic compound in the weld region.

Technical Note:A Major Loss in Tensile Strength of Friction Stir Welded Aluminum Alloy Joints Resulting from Atmospheric Corrosion

The effect of corrosion on the mechanical properties of aluminum alloy (AA6005-T6) joints produced by friction stir welding is investigated. The tensile strength of the weldments was analyzed after...

Comparison of the Optimized Process Parameters of Double-Sided Friction Stir Welded Aluminium Alloy Joints Using Statistical and Evolutionary Techniques

One of the most innovative solid state welding techniques used in the aerospace, automotive, defence, rail and marine industries is Friction Stir Welding (FSW) process, as it is used for joining aluminium, copper and magnesium alloys. The weld quality is decided by the FSW process parameters such as rotational speed, welding speed and pin profile. A regression model was developed relating the welding input parameters (tool rotational speed, welding speed and pin profile) and the output response parameters (tensile strength, hardness and toughness) based on the experiments carried out with the help of Response Surface Methodology. The obtained regression equations were used in determining the optimal welding process parameters. A new method, Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) based on evolutionary algorithm has been used in the optimisation. The optimum results gathered from the desirability approach through Response Surface Methodology (RSM) were compared with those obtained through the evolutionary algorithm. The results show that the proposed evolutionary method is much effective, faster than the desirability approach discussed in the work.

Characterization of the tensile properties of friction stir welded aluminum alloy joints based on axial force, traverse speed, and rotational speed

Friction stir welding (FSW) process has gained attention in recent years because of its advantages over the conventional fusion welding process. These advantages include the absence of heat formation in the affected zone and the absence of large distortion, porosity, oxidation, and cracking. Experimental investigations are necessary to understand the physical behavior that causes the high tensile strength of welded joints of different metals and alloys. Existing literature indicates that tensile properties exhibit strong dependence on the rotational speed, traverse speed, and axial force of the tool that was used. Therefore, this study introduces the experimental procedure for measuring tensile properties, namely, ultimate tensile strength (UTS) and tensile elongation of the welded AA 7020 Al alloy. Experimental findings suggest that a welded part with high UTS can be achieved at a lower heat input compared with the high heat input condition. A numerical approach based on genetic programming is employed to produce the functional relationships between tensile properties and the three inputs (rotational speed, traverse speed, and axial force) of the FSW process. The formulated models were validated based on the experimental data, using the statistical metrics. The effect of the three inputs on the tensile properties was investigated using 2D and 3D analyses. A high UTS was achieved, including a rotational speed of 1050 r/min and traverse speed of 95 mm/min. The results also indicate that 8 kN axial force should be set prior to the FSW process.

Modelling of the Effect of Process Parameters on Tensile Strength of Friction Stir Welded Aluminium Alloy Joints

Friction stir welding (FSW) process is a promising solid-state joining process with the potential to join low-melting point material, particularly, aluminium alloy. The most attractive reason for joining aluminium alloy with this process is the avoidance of the solidification defects formed by conventional fusion welding processes. In this article, an attempt has been made to develop an empirical relationship between FSW variables and tensile strength. Central composite rotatable design was used by considering four factor and five levels, which enables to quantify the direct and interactive effect of four numeric factors, that is, tool rotational speed, welding speed, axial force, and tapered pin diameter on the tensile strength. The developed relationship is useful for prediction of tensile strength in friction stir welded AA6082 aluminium alloy joints at 95% confidence level. It will also be helpful for selection of process variable to obtain desired strength of the joint. Furthermore, the optimized capabilities in design-expert software were used to numerically optimize the input parameters. At the optimal parameters, three experiments were conducted to compare the predicted value of tensile strength with the experimental value.

Microstructure and mechanical properties as a function of rotation speed in underwater friction stir welded aluminum alloy joints

A 2219-T6 aluminum alloy was underwater friction stir welded at a fixed welding speed and various rotation speeds in order to illuminate the influence of rotation speed on the performance of underwater joints. With increasing rotation speed, the hardness of the stir zone (SZ) gradually increases due to the increase in dislocation density. The tensile strength first increases from 600 to 800 rpm and then reaches a plateau in a wide rotation speed range. After that a remarkable decrease in tensile strength occurs owing to the formation of void defect. The joint welded at lower rotation speed tends to be fractured in the SZ. At higher rotation speeds, the hardness increase in the SZ makes the fracture locations of defect-free joints move to the thermal-mechanically affected zone (TMAZ) or heat affected zone (HAZ).

Observation of the Behavior of Fatigue Cracks in Friction Stir Welded Aluminum Alloy Joints

Friction stir welding (FSW) is a new solid-state welding process that can produce low-cost and high-quality joints of especially aluminum and mgnesium alloys. The welding zone consists of different regions with characteristic microstructuralal details such as a weld nugget, a thermo-mechanically-affected zone (TMAZ) and a heat-affected zone (HAZ). Tension-compression fatigue tests were performed using FSW aluminum alloy AA5454 sheet specimens at a stress ratio of –1. To investigate the propagation behavior of small fatigue cracks in those regions, an artificial defect was introduced into different defined locations in the FSW specimens as well as into the parent material specimens. The crack propagation rates depended on the defined locations and were a function of the hardness; that is, the lower the hardness was, the higher the propagation rate was. The crack paths were mostly perpendicular to the applied stress axis, but some crack paths exhibited deviations by the influence of the local anisotropy of the microstructure.

Fatigue Crack Characteristics of Friction Stir Welded Aluminum Alloy Joints

Fatigue strength of Al5083-O FSW joints was evaluated in the relation of the FSW conditions. Static strength of the joints in a range of FSW conditions was the same as that of base metal. Because the fracture of the joints occurred at the base metal in the tensile tests. Therefore the joint efficiency in tensile strength of joints with the FSW condition of tool rotation: 800 rpmwelding speed: 100 mm/min (800-100), 800-200 and 500-100 are all hundred percent. However, the fatigue strength of those joints with fine static strength varied very much. The joint efficiency for fatigue strength varies from 75% for 500-100 to 31% for 800-200. Crack path in fatigue test was always initiated at the center of back surface of FSW weld zone, and propagated through stir zone. Crack growth rate measurement and fracture surface analysis resulted the difference of the joint efficiency has a connection with the incomplete welding at back surface of joints.

Fatigue Strength of Friction Stir Welded Aluminum Alloy Joints

Strength of Al5083-O FSW joints was evaluated, in relation to FSW conditions. Static strength of the joints was found to be enough because base metal fracture occurred in the tensile tests of joints for some FSW conditions. However, the fatigue strength of those joints with fine static strength varied significantly. For example, in tensile strength of joints with the FSW condition with tool rotation: 800 rpm- welding speed: 100 mm/min (800-100), 800 rpm-200 mm/min (800-200) and 500 rpm- 100 mm/min (500-100), each condition of FSW joint efficiency were all hundred percent. In contrast, joint efficiency for fatigue strength varied from 75% for 500-100 to 31% for 800-200. Crack path in fatigue test was always initiated at the center of back surface of FSW weld zone, and propagated through stir zone. The variance of fatigue strength is believed to be attributed to the stirred condition at back surface.