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An ultrasonic vibration setup has been designed and fabricated to make a comparative study between conventional frictions stir processing and ultrasonic assisted friction stir processing. Effects of ultrasonic vibrations on rotational speeds as well as processing speeds are studied. A series of experiments are performed to determine effect of ultrasonic vibrations. From the experimental results, it is seen that ultrasonic vibrations help in generating high heat in the stirred zone of friction stir processing which causes intense plastic deformation and improves material flow. By using the ultrasonic vibrations, higher hardness and tensile strength of friction stir processed joints are evident. Further axial force and transverse force reduction is also visible in case of ultrasonic assisted friction stir processing.

Increasing demands for operating properties of fabricated elements on one hand, and a necessity of reducing mass of a structure on the other, triggers materials engineering research into producing surface layers representing required functional properties. Methods commonly used in the production of surface layers, such as surfacing, spraying or re-melting with a laser beam have been known for years. A new method is the friction stir processing (FSP) of surface layers. The FSP process is primarily used for the modification of microstructure in near-surface layers of processed metallic components. In particular, the process may produce: fine grained structure, surface composite, microstructural modification of cast alloys, alloying with specific elements, improvement of welded joints quality. The chapter is composed of a few main parts. In the first part, based on literature review the main application and achievements of FSP processes are presented. In the second part: analysis of the process. The third part is focused on microstructure refinement and the last part provide information about friction stir alloying as well as friction stir processing with ultrasonic vibration.

The present work accomplished homogenously disseminated ZrB 2 reinforcement particles and very fine grain structure by multipass friction stir processing (MPFSP) of AA6082. They observed the influence of reinforcement particle ZrB 2 on the microstructure and tensile properties of the MPFSP. The coarse dendrite structure of the base material AA6082 was studied using ZrB 2 nanoparticles. The MPFSP/ZrB 2 successfully shattered these coarse and dendrite clusters, resulting in a uniform microstructure in the stir zone. The MPFSP has observed material flow around the cluster's redistribution. At increased ZrB 2 concentration, SEM and EBSD examinations demonstrated that ZrB 2 reinforcement particles strongly inhibited grain boundary migration, resulting in a continual reduction in grain size and HAGBs fraction. The tensile properties and microstructure of the MPFSP/ZrB 2 of AA6082 were enhanced using a rotational tool speed of 1120 rpm, welding speed of 125 mm/min, and tilt angle of 2°. The reinforcement particles ZrB 2 were fragmented completely and uniformly disseminated in the 4th FSP pass. As the FSP increases, the ZrB 2 agglomeration reduces. The base metal AA6082's ultimate tensile strength (UTS) was 191 ± 8 MPa with a % strain of 20 ± 0.8. After MPFSP/ZrB 2 on AA6082, the UTS was increased as the FSP pass increased. The higher UTS (266 ± 5) was observed at the 4th FSP pass.

The current research designed a statistical model for the bobbin tool friction stir processing (BT-FSP) of AA1050 aluminum alloy using the Response Surface Method (RSM). The analysis studied the influence of tool travel speeds of 100, 200, and 300 mm/min and different pin geometries (triangle, square, and cylindrical) at a constant tool rotation speed (RS) of 600 rpm on processing 8 mm thickness AA1050. The developed mathematical model optimizes the effect of the applied BT-FSP parameters on machine torque, processing zone (PZ) temperature, surface roughness, hardness values, and ultimate tensile strength (UTS). The experimental design is based on the Face Central Composite Design (FCCD), using linear and quadratic polynomial equations to develop the mathematical models. The results show that the proposed model adequately predicts the responses within the processing parameters, and the pin geometry is the most influential parameter during the BT-FSP of AA1050. The analysis of variance exhibit that the developed mathematical models can effectively predict the values of the machine torque, PZ temperature, surface roughness, hardness, and UTS with a confidence level of over 95% for the AA1050 BT-FSP. The optimization process shows that the optimum parameters to attain the highest mechanical properties in terms of hardness and tensile strength at the lowest surface roughness and machine torque are travel speed (TS) of 200 mm/min using cylindrical (Cy) pin geometry at the constant RS of 600 rpm. The PZ temperature of the processed specimens decreased with increasing TS at different pin geometries. Meanwhile, the surface roughness of the processed passes and machine torque increased with increasing the TS at different pin geometries. Increasing TS from 100 to 300 mm/min increases the hardness values of the processed materials using different pin geometries. The highest UTS of 79 MPa for the processed specimens was attained at the TS of 200 mm/min and RS of 600 rpm using the Cy pin geometry.

AA1050 plates of 8 mm thickness were processed via bobbin-tool friction stir processing technique at a constant rotation speed of 600 rpm and different travel speeds ranging from 50 to 300 mm/min using three-pin geometries of triangle, square, and cylindrical. The temperatures of the processed zone, the advancing side, and the retreating side were measured; the machine torque during processing was also recorded. The processed materials were evaluated in terms of surface roughness, macrostructure, tensile properties, and hardness measurements. The fracture surfaces of the tensile fractured specimens were investigated using SEM. The results indicated that the pin geometry and processing speed significantly affect the generated heat input and the morphology of the processed zone. The peak temperature in the center of the processed zone decreases with increasing the travel speed from 50 to 300 mm/min at all applied pin geometries. The maximum temperature of ~400 °C was reached using the cylindrical pin geometry. The machine torque increases with increasing the travel speed at all applied pin geometries, and the highest torque value of 73 N.m is recorded using the square pin geometry at 300 mm/min travel speed. The top surface roughness of the processed area using the cylindrical pin is lower than that given by the other pin geometries. Under all applied conditions, the hardness of the processed area increases with increasing travel speed, and the cylindrical pin shows a higher hardness than the other pin geometries with 19% enhancement over the BM. The AA1050 processed using a cylindrical pin at 200 mm/min travel speed and a rotation speed of 600 rpm produces a sound processing zone with the highest ultimate tensile strength of 79 MPa.

In the Wire Arc Additive Manufacturing (WAAM) process of aluminum alloys, abnormal metallurgical behavior leads to defects in the material, such as porosity, cracks, and large grain sizes with varying directions and orientations, resulting in poor mechanical properties of the product. This paper discusses further research on Friction Stir Processing (FSP) applied to the surface of aluminum alloys after WAAM, aiming to minimize material defects and break down coarse grains to enhance the mechanical properties. Test specimens were produced through a hybrid manufacturing process combining WAAM and FSP on the formed material ultrasonic testing, tensile testing, and metallography were conducted to observe changes in microstructure and mechanical properties of the test material. Ultrasonic testing demonstrated the material’s uniform density and detected minimal defects, indicative of high-quality integrity. From the tensile test results, it was found that the sample material’sultimate tensile strength and yield strength increased compared to the initial condition. Metallographic testing also provided visual evidence that FSP treatment caused most grains to undergo plastic deformation and dynamic recrystallization, resulting in finer grain sizes and improved mechanical properties. From a series of test results, it can be concluded that FSP is a highly effective technique for improving the microstructure and mechanical properties of WAAM-produced aluminum alloys

A new method to achieve friction stir processed parts with higher wear resistance and lower residual stress values was presented. The underwater stationary shoulder FSP process (USSFSP) was investigated using experimental and numerical methods. Also, the presented process was compared with the conventional underwater FSP method (UCFSP). An improved CEL simulation method was used to prevent errors in the contact boundary between Eulerian and Lagrangian domains. Heat input was reduced significantly and resulted in a fine microstructure with higher microhardness and lower residual stresses. Temperature field was concentrated around the pin and caused a symmetrical residual stress distribution. The distribution area of Von-Mises and longitudinal stresses during the USSFSP was significantly narrower than the UCFSP process. The stress distribution around the UCFSP tool was compressive, and tensile stress was produced at further distances. However, the longitudinal stress distribution in the USSFSP was completely opposite. Tensile stress was generated in the lower part of the thickness and compressive stress in the upper part and in locations away from the centerline. This method caused the formation of a compressive residual stress region and considerably reduced the width of the tensile residual stress zone. By increasing the hardness and decreasing the residual stress level, the USSFSP proved to be instrumental in improving the material’s wear resistance. The wear rate in the stir zone undergoes a substantial reduction, decreasing from 5.6 × 10 −3 mm 3 /m in UCFSP to 1.4 × 10 −3 mm 3 / m in USSFSP.

A new variant of friction stir processing named upward friction stir processing (UFSP) is a promising approach to control particles’ distribution and promote a more uniform distribution over a larger processed area. This variant involves using two sheets with functional particles between them to produce metallic composites. A spacer is used to ensure the desired quantity and uniform distribution of the particles and prevent sputtering. This technique promotes an upward flow to introduce more particles with a uniform distribution in the processed volume, avoiding discrete holes or grooves. This study involved enhancing the particles’ distribution by varying process parameters. The resulting trial with the best particles’ distribution was characterized by means of light microscopy, eddy current testing, microhardness mapping, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The study revealed that UFSP can improve the particles’ distribution in the stir zone of metallic composites, especially when multi-passes are performed towards the retreating side of the plates. The process parameters that produced an improvement in particles’ distribution were six passes with an offset of 1 mm towards the retreating side, the tool rotation and processing speed of 900 rev/min, and 180 mm/min, respectively, and a spacer’s thickness of 0.5 mm. The resulting hardness and electrical conductivity profiles show that the UFSP technique can significantly affect material’s properties, including mechanical strength, particularly when processing with tool offset towards the retreating side. Furthermore, the hardness increased by about 22% in composites produced with the addition of reinforcement particles. However, for some aluminum alloys, the properties decreased under such conditions. These findings highlight the potential of UFSP for producing functionalized materials with tailored properties, while also underscoring the importance of careful parameters selection to optimize the material´s performance.

The present research will focus on the properties of mechanical and wear of AA6082 matrix metal composites reinforced with SiCNP nanoparticles through the FSP technique. The fiber reinforcement particle (FSP) technique represents a sophisticated approach that facilitates uniform distribution of reinforcing particles within the metal, thereby enhancing performance. The current study investigated an uncommon technique in metal matrix composites: the impact of FSP process parameters, specifically the tool rotation speed, movement speed, and nanoparticle concentration, on the generated composites. This demonstrated how the composite materials behaved mechanically and provided accurate examination of the materials’ minute features. In order to determine the material’s wear resistance in practice, they used a volume loss rate and a specified wear coefficient. The microscopic investigation revealed that the grains in the aluminum alloy matrix were tiny and evenly dispersed alongside the silicon carbide nanoparticles, indicating reinforcement. They used established methodologies for estimating the mechanical properties of the materials, namely tensile strength and yield values, as well as ductility. The physical properties of the AA6082/SiC composites outperformed those of the unreinforced Aluminum alloy. The key reason for increasing the mechanical properties was the reinforcement with SiC particles and the fabrication of finer grains using FSP. Sliding wear tests were also conducted. The smaller, more durable SiC particles in the FSP composites reduced friction-induced wear and outperformed the original alloy in terms of wear resistance. The procedures were additionally assessed for several wear behaviors such as grating, binding, and shearing off.

An inhomogeneous microstructure induced by high rotating speed submerged friction stir processing (HRS-SFSP) on 6061 aluminum alloy was researched in detail.The microstructures of the aluminum alloy processing zone were characterized by electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) qualitatively and quantitatively.The results show that the recrystallization proportion in the inhomogeneous structure of the processing zone is 14.3%, 37.8% and 35.9%, respectively. Different degrees of grain deformation can affect the dislocation and lead to the formation of a plastic–elastic interface. At the same time, the second-phase particles in the processing zone were inhomogeneity and relatively, which further promotes the plastic–elastic interface effect. The plastic–elastic interface can significantly improve the strength of aluminum alloy, whileat the same time, rely on recrystallized grains to provide enough plasticity. When the rotation speed was 3600 r/min, the strength and ductility of the aluminum alloy after HRS-SFSP were increased by 48.7% and 10.2% respectively compared with that of BM. In all, the plastic–elastic interface can be formed by using high rotating speed submerged friction stir processing, and the strength-ductility synergy of aluminum alloy can be realized at the plastic–elastic interface.