Friction Stir Welded Aluminum Alloy Research Articles

Enhancing Predictive Capabilities: Machine Learning Approaches for Predicting Mechanical Behavior in Friction Stir Welded Aluminum Alloys

Enhancing Predictive Capabilities: Machine Learning Approaches for Predicting Mechanical Behavior in Friction Stir Welded Aluminum Alloys

Optimization of 2024-T3 Aluminum Alloy Friction Stir Welding Using Random Forest, XGBoost, and MLP Machine Learning Techniques.

This study optimized friction stir welding (FSW) parameters for 1.6 mm thick 2024T3 aluminum alloy sheets. A 3 × 3 factorial design was employed to explore tool rotation speeds (1100 to 1300 rpm) and welding speeds (140 to 180 mm/min). Static tensile tests revealed the joints' maximum strength at 87% relative to the base material. Hyperparameter optimization was conducted for machine learning (ML) models, including random forest and XGBoost, and multilayer perceptron artificial neural network (MLP-ANN) models, using grid search. Welding parameter optimization and extrapolation were then carried out, with final strength predictions analyzed using response surface methodology (RSM). The ML models achieved over 98% accuracy in parameter regression, demonstrating significant effectiveness in FSW process enhancement. Experimentally validated, optimized parameters resulted in an FSW joint efficiency of 93% relative to the base material. This outcome highlights the critical role of advanced analytical techniques in improving welding quality and efficiency.

Microstructure, microhardness and mechanical behavior of dissimilar AA7075/AA6061 alloys under friction stir welding

Friction stir welding (FSW) of dissimilar AA6061 and AA7075 aluminum alloys faces challenges such as an unclear forming mechanism and low welding efficiency. In order to improve welding efficiency and elucidate the variations in metallography, Microhardness, and mechanical properties of dissimilar alloy FSW joints, this article designed FSW experiments using the Taguchi method with welding speeds ranging from 600 to 1000 mm/min. We studied the relationship between material mixing and welding defects through macroscopic metallography, microscopic metallography, and Microhardness, while the impact of welding parameters on the microstructure and properties was evaluated. The results show that void defects do not exist in dissimilar alloy FSW joints, and the Microhardness changes are “U” and “W” shaped. Material mixing played a decisive role in determining the microstructure and properties of dissimilar aluminum alloy FSW joints, with increased rotational speed enhancing material flow. The order of influence on the mechanical properties of the joint was found to be plunge depth, welding speed, and rotational speed. Under the conditions of 1000 mm/min, 2400 rpm, and 0.25 mm, the yield strength (YS) and ultimate tensile strength (UTS) of the dissimilar alloy FSW joints reached 87.3% and 73.4% of the AA6061-T6 alloy, respectively.

Effect of tools rotational speed on the mechanical properties of one-step double-acting friction stir welded aluminum alloy AA 6061 hollow panel

The utilization of Aluminum hollow panels enhances structural strength while simultaneously ensuring a lightweight and efficient use of materials. During their application, these panels necessitate a welding process that is susceptible to porosity due to the disparity in hydrogen gas solubility between liquid and solid aluminum. Solid-state welding techniques, such as Friction Stir Welding (FSW), have proven to be effective and appropriate solutions for overcoming this issue. However, due to the thickness of the hollow panels, FSW process is unfeasible as it requires welding on both sides, resulting in prolonged production times. Consequently, the development of a one-step double-acting FSW technique becomes necessary, involving the simultaneous utilization of two tools. The usage of two tools introduces two sources of friction-stir forces, heat, and axial forces, demanding an assessment of the novel response from the specimens. This research aims to analyze the effect of a specific parameter, namely the tool rotation speed, within the one-step double-acting FSW process on the physical and mechanical properties of the AA6061 hollow panels. The One-Step Double-Acting FSW process involved conducting variations in the tool rotation speed on both sides of the welds. Specifically, for the 4G weld position (underside of the workpiece with an overhead weld position), speeds of 1200, 1500, and 1800 rpm were employed. Meanwhile, a consistent rotation speed of 1500 rpm was maintained for the 1G weld position (overside of the material with a flat weld position). The transverse speed and tilt angle are set at 30 mm/min and 2°, respectively. Elevating the tool rotation speed results in increased hardness, load capacity, and bending strength of the weld joints. The specimen subjected to the highest rotational speed (1800 rpm) exhibits the most exceptional mechanical properties, including a hardness of 73.46 HVN, load capacity of 18.47 kN, and bending strength of 60.56 MPa.

Microstructural and corrosion behaviours of dissimilar friction stir welded aluminium alloys

In this study, the friction stir welding (FSW) process was employed to investigate the effect of tool geometry on the corrosion behaviour and microstructure of friction stir welded AA7075-7651 and AA1200-H19 using Central Composite Design. The workpieces were machined and welded, and the interfaces were milled. A 2-level full factorial experimental design was deployed using Response Surface Methodology (RSM). A rotational speed of 1500 rpm, welding speed of 30, 60, and 90 mm/min, and a 2° tilt angle of the tool with a plunge force of 7 kN were utilized. The results show that regardless of the tool geometry, multi-response optimum weldment can be achieved at 60 mm/min welding speed and a tilt angle. The microstructure of the optimal weldments presents an ‘onion ring’ pattern, indicating proper mixing of the alloys during FSW. Analysis of the corrosion behaviour revealed a decrease in the polarization resistance when the transverse speed increased from 30 to 90 mm/min, as polarization resistance has a direct relationship with corrosion rate. It can be concluded that FSW ensures excellent weldment, as evident in the microstructural evolution of the resulting weldments, and that tool geometry plays a significant role in the corrosion inhibition efficiency of the alloys.

Development of a T-Joint Welding Fixture for Enhanced Friction Stir Welding Performance

Welding, a crucial manufacturing process across various industries, involves forming permanent component joints. Friction stir welding (FSW), an efficient technique is employed for this purpose. FSW requires a fixture to securely hold the workpiece during welding, ensuring precise alignment, minimal deformation and effective heat dissipation. This work focuses on designing a fixture tailored for T-joint configuration FSW of aluminum alloys. Initial concept design was refined for optimal performance with material selection (Mild Steel and EN8) based on requirements. Real-time welding conditions were considered for analysis, leading to the choice of EN8 due to reduced deformation. This paper outlines the steps involved in designing, analyzing and manufacturing a T-joint welding fixture, guaranteeing proper alignment, clamping and heat management during welding.

Dissimilar friction-stir welding of aluminum alloys 2519, 6061, and 7050 using an additively-manufactured tool

This work was undertaken to evaluate the feasibility of the additively-manufactured tool for dissimilar friction-stir welding (FSW) of 2519, 6061, and 7050 heat-treatable aluminum alloys. The tool design included a flat shoulder with an Archimedean spiral groove and a threaded probe with a Triflute profile. It was found that the application of such a tool provided a nearly twofold decrease in Z-force and essentially enhanced the mechanical mixing of dissimilar materials within the stir zone. Nevertheless, despite the enhancement effect, FSW was inefficient for a homogeneous intermixing of dissimilar materials, and a distinct interface boundary was present within the stir zone. It was also found that the mechanical performance of the welded joints was sensitive to the initial temper condition of the welded alloys. Specifically, FSW of the alloys in the solution-annealed condition provided no significant influence on material strength, while that in the precipitation-hardened state led to significant material softening. During the post-weld T6 treatment, extensive nucleation of silicon-rich particles was found to occur at this interface. It was deduced that those promoted cracking during transverse tensile tests, thus giving rise to the decohesion of the dissimilar welds along the interface boundary. Hence, the post-weld T6 treatment was concluded to be unfeasible for dissimilar aluminum welds.

Effect of pre-corrosion on crack initiation behavior of friction stir welded aluminum alloy 2024-T3 in high and low cycle fatigue regimes

The effect of microstructural inhomogeneity and pre-corrosion in 3.5% NaCl solution is investigated on the fatigue crack nucleation behavior of welded AA2024-T3. The localized corrosion affects the heat-affected zone more than the weld nugget zone. The formation of corrosion pits often occurs in the region between the adjacent Al-matrix and intermetallic particles due to the reverse polarity behavior of S-phase precipitates (Al2CuMg) in the saltwater environment. Further, the long-term stability of the welded joint is examined by immersing the specimens in 3.5% NaCl solution for different time intervals ranging from 10 hrs to 200 hrs. After 100 hrs of immersion in the salt water, high and low cycle fatigue behavior of the corroded samples has been examined. Long-term exposure to the saltwater environment results in intergranular corrosion due to localized pitting. The micro-mechanism of the pitting process under salt water and its effect on fatigue lives is studied.

Study on the Properties of a 2219 Aluminum Alloy Friction Stir-Welded Joint under the Biaxial Stress State

Friction stir welding (FSW) has been considered ideal for aluminum alloy structures. The performance of FSW joints under unidirectional stress state has been widely tested, but there is still a lack of experimental data under a biaxial stress state. For accurate characterization of the mechanical properties of 2219 aluminum alloy FSW joints under a biaxial stress state, this article conducted biaxial tests. The FSW joint was tested using scanning electron microscopy (SEM) to obtain its microscopic properties and obtain the partition results of the welded joint. The stress–strain relationship and yield characteristics of welded joints under different loading ratios were studied using biaxial tensile tests of cruciform specimens combined with digital image correlation technology. By comparing it with the existing yield criteria, the yield criterion suitable for FSW joints of 2219 aluminum alloy under a biaxial tensile load was determined.

Study on stress corrosion properties of aviation aluminum alloy friction stir welded joint at the different strain rate

Aviation aluminum alloy welded structures are subjected to stresses at different strain rates in corrosive environments such as the ocean. Studying the stress corrosion properties of aviation aluminum alloy Friction Stir Welding (FSW) structures is essential. Therefore, this paper focuses on the study of 12 mm thick 7085-T7452 high-strength aviation aluminum alloy FSW joints under different strain rates of stress corrosion properties changes and the impact of welding process parameters. The main conclusions of this thesis are as follows: For the base material (BM) and the aluminum alloy FSW joints, when the strain rate increased from 10−7 s−1 to 10−5 s−1, the stress corrosion strength increased, and the stress corrosion cracking (SCC) sensitivity index ISSRT decreases. The SCC sensitivity at the same strain rate: SS-400-120 > SS-300-60 > SS-300-120 > BM. After the Slow strain rate tensile (SSRT) test, the FSW joint fracture in the air is a transgranular ductile fracture. Meanwhile, the fracture is a ductile-brittle hybrid fracture in 3.5% NaCl solution, and the number of secondary cracks along the grain boundary increased significantly, showing obvious SCC sensitivity. The BM fracture after SSRT is ductile, showing lower SCC sensitivity.

Study on infrared emissivity model based on perturbation method and Kirchhoff approximation and its application in aluminum alloy welding

Infrared temperature measurement ubiquitously finds applications across multifarious domains. The surface infrared emissivity constitutes the critical parameter influencing the precision of infrared temperature measurement. Therefore, investigating the surface infrared emissivity is of tremendous significance. This paper establishes an infrared emissivity analytical model for rough texture surfaces by considering the repercussions of roughness on the infrared emissivity of material surfaces. First, power spectrum analysis of random roughness is performed. The positive and negative power law components of the rough surface model are constructed using the Monte Carlo method and fractal theory, respectively. Second, based on the perturbation method and Kirchhoff approximation, the infrared emissivity model for rough textured surfaces is established. Third, the infrared emissivity of rough textured surfaces with different fractal dimensions (D), characteristic length scales (G), and surface textures is simulated using the FDTD optical simulation software to validate the efficacy of the infrared emissivity model. Finally, the infrared emissivity model is applied to the temperature measurement system of aluminum alloy friction stir welding. The infrared measurement precision before and after rectification is contrasted and scrutinized to validate the accuracy of this model.

Effect of a novel intermediate heat treatment process on abnormal grain growth in 2219 aluminum alloy friction stir welds

The abnormal grain growth occurs in 2219 aluminum alloy friction stir welds during solution treatment, which results in the deteriorating mechanical properties of the weld. In this paper, a novel intermediate heat treatment process after friction-stir welding, including rapid heating and high-temperature treatment at 560 °C and annealing treatments, was proposed to suppress abnormal grain growth in the weld during subsequent solution treatment. The effect of the intermediate heat treatment process on the microstructure and mechanical properties of the weld was investigated and analyzed. The results show that the grains in the nugget zone grow continuously in a short time at a temperature higher than the eutectic line. There is no abnormal grain growth in most regions of the weld treated with the intermediate heat treatment after solution treatment. Compared with tailor-welded blanks directly with solution treatment, the elongation of the tailor-welded blanks treated with the intermediate heat treatment and solution treatment increases from 13.5% to 20% because of the improvement of weld strength. The increase in mechanical properties is more significant after artificial aging treatment. Because of the disappearance of the pinning effect of particles at high-temperature treatment, abnormal grain growth induced by particles cannot occur. The grains grow normally, improving their ability to resist abnormal grain growth during solution treatment. Fine grains result in a more uniform distribution of deformation in the solution-treated weld. Furthermore, it is more difficult for the particles at the grain boundary to cause crack propagation along the grain boundary after artificial aging treatment. This work helps guide how to suppress abnormal grain growth in the weld and further deepen the understanding of the phenomenon.

Microstructural analysis of cooling tank-assisted hybrid friction stir welded aluminium alloys: a novel approach

The friction stir welding process is a solid-state technique for joining similar and dissimilar alloys. The advanced fixture was designed and fabricated for welding of the aluminum plate by a hybrid fabricated fixture on a vertical milling center. The storage tank was designed and attached at the bottom of the base plate of the fixture. The three different cooling media used in the cooling tank as air, water, and coolant. The welded samples were examined for mechanical and metallurgical performance. The optimization of process parameters was done for the tensile Test as output. The coolant as a fluid in the tank results in maximum tensile strength at 500 rpm. The microstructural characterization of the heat-affected zone was also done. The weld thinning and quenching are the main problems of direct cooled FSW. This problem is not found in the indirect cooled FSW welding method. The storage tank provided uniform heating and cooling during welding that reduced the thermal quench and microstructural problems. The SEM and EDX mapping images showed the effect of different cooling media on the FSW samples. The microhardness was analyzed to identify different microstructural zone and the hardness of welded part.

Effect of metal powder properties of reinforced friction stir welded blanks on springback phenomenon

The influence of properties of metal powder reinforcement in the weld zone of friction stir welded blanks on springback is investigated. The weld zone properties of friction stir welded aluminum alloys namely AA5052 and AA8011 were modified by reinforcing metal powders like Al and Cu at different volume fractions. Tensile behavior of unreinforced and metal powder reinforced friction stir welded blanks was monitored by tensile test, and springback was evaluated through the V-bending process. The results show that the tensile strength and ductility increase with an increase in volume fraction of both types of powder reinforcement up to a certain level after which decrease. There is about a 7% reduction in springback with a maximum level of 1.2 vol% of both types of reinforcements as compared with unreinforced welded blanks. This study helps us select suitable properties of reinforcing material to improve the mechanical properties and to reduce springback of tailor welded blanks.

Study of Mechanical Behavior and Pitting Corrosion Resistance of Friction Stir Welded Aluminium Alloys 2219-T87

High strength AA2219-T87, Al-Cu alloy of 6mm plates were friction stir welded. Microstructures, micro hardness values, tensile properties and corrosion analysis were studied in the welded condition. The stirred region of the welded specimen looked like a rectangular shape, with a weld flow arm moving towards the top surface of the welded plates on each side of the welded region. Presence of CuAl2 particles found to be large in size in the base material of 2219 when compared to those in the weld nugget. The welded region 2219-2219 showed better pitting and general corrosive resistance compared to the 2219 parent metal.

Quasi-in-situ characterization of microstructure evolution in friction stir welding of aluminum alloy

The in-situ investigation of microstructure evolution during friction stir welding (FSW) can provide very important theoretical guidance to control the microstructure and mechanical properties of the FSW joint. In this study, a quasi-in-situ investigation method of the microstructure evolution in friction stir welding of AA1050 aluminum alloy was developed. The microstructure along the material flow path was characterized and analyzed by taking the strain, strain rate, and temperature into account simultaneously. The results show that the microstructure evolution during the FSW of aluminum alloy can be divided into four stages according to the material flow state and thermal history. Firstly, grain coarsening by static recovery and static recrystallization occurs at the static preparatory stage (or called the preheating stage). Secondly, grain refining by continuous dynamic recrystallization occurs at the acceleration stage, where the temperature gradually increases to nearly a constant. The grain size is mainly controlled by the accumulative total strain. The strain rate only affects the rate of dislocation generation and the type of β-fiber simple shear texture components. Thirdly, at the high-velocity flow stage, a dynamic equilibrium between plastic deformation and dynamic recrystallization is maintained, and the grain size only fluctuates within a small range. Finally, a second grain-coarsening process occurs through normal grain growth due to thermal activation at the deceleration stage. This process is inevitable because it occurs under the cover of the tool shoulder. The grain coarsening during the normal cooling stage was avoided in this study due to the rapid cooling used, which has been widely reported by published documents.

Influence of Tool Eccentricity pin Positioning on AA6061 Aluminium Alloy Friction Stir Welds

This study examines the influence of tool eccentricity pin positioning on AA6061 aluminium alloy friction stir welds. A laser scanning confocal microscope and optical microscope was used to analyze the surface roughness and the cross-sectional microstructure of the samples. Surface roughness analysis reveal the thread-to-flat (T2F) samples show rougher surface with increasing rotational speed up to 1400 rpm. On the other hand, the surface appearance of flat-to-thread (F2T) samples show minimal change. Cross-sectional microstructural observations show that the stir zone area of both groups increases with increasing rotational speed. However, the periodic bands in T2F and F2T samples increases in the upper region and lower region of the stir zone, respectively.

Effect of boron carbide reinforcement particles on microstructure and mechanical properties of dissimilar friction stir welded aluminum alloys

The current work investigates the role of boron carbide (B4C) reinforcements on the material flow, microstructure and mechanical properties of dissimilar friction stir welded Al5083-6061 aluminum alloys. Four different weld composites were prepared with varying B4C composition (0–4%). The fine B4C particles were added at the adjoining edges by a novel reinforcing technique along the weld line. Optical and scanning electron microscopes were used to study the B4C distribution, dissolution, bonding and fracture regions. The B4C pinned the grain boundaries and the fine grain structure is obtained by preventing the grain growth during the recrystallization process. Mechanism of microstructure evolution in the stir zone with B4C is attributed to dynamic recovery, dynamic recrystallization and particle stimulated nucleation. The highest hardness and strength were obtained in the joint processed with 2% B4C reinforcements. The tensile test results reveal that the weld composite exhibits higher strength not only by decrease in grain size but also due to grain refinement strengthening and orowan strengthening mechanisms which are occurred due to addition of B4C particles.

Effects of different cooling conditions on microstructure and precipitation behavior of fine-grained Al–Zn–Mg–Cu alloy friction stir welding joint

The microstructure evolution and precipitation phase distribution of 7075 aluminum alloy friction stir welding (FSW) joint were investigated under liquid CO2 cooling conditions. The fine grained 7075 aluminum alloy was developed by four-pass equal channel angular pressing (ECAP) and FSW joints with CO2 cooling at room temperature. It was found that CO2 cooling could effectively reduce the peak temperature of the weld, leading to a refinement of the welded grain and an improvement of the welded joint. Various recrystallization mechanisms were found in different areas of the weld. The grain boundary and dislocation density of large angles gradually decreased from the weld stir-zone (SZ) to the heat-affected-zone (HAZ) regions, and the anisotropy increased. The type of precipitated phase and the relationship with the matrix interface were determined by detecting the spacing between the precipitated phase and the crystal plane of the matrix. CO2 forced cooling not only enhanced the matrix dislocation strengthening and grain boundary strengthening, but also effectively improved the size and type of precipitated phases and the colattice strengthening effect. In addition, liquid CO2 cooling can greatly reduce the PFZ width and enhance the Zener pinning effect.

X-ray quantification of second-phase precipitates in friction-stir welded 2519-T820 aluminum alloy

In this study, a new X-ray approach was applied to quantify the second-phase precipitates in the friction-stir welded 2519-T820 aluminum alloy. It was found that the stir zone material contained a significant fraction of secondary phases, including the non-equilibrium θ′ and θ″ ones. Based on this result, it was concluded that the widely accepted concept of FSW-induced precipitation phenomena is oversimplified and requires revision.