Chapter 4 - Case Study of Aluminum 5083-H116 Alloy

Friction stir welding is a novel solid state joining process for making low cost, energy efficient butt welds in aluminum alloy extrusions. The plate edges are clamped against a backing plate and the material is plastically deformed and stirred by a rotating tool moving along the joint line. The resulting weld bead is flush with the surface and exhibits little distortion. The material in the weld and heat affected zone (HAZ) has a fine-grained microstructure and a high tensile strength compared with welds produced by conventional arc welding methods. The present investigation was undertaken to determine the fatigue properties of friction stir welds in 5 mm thick plates in an AA6082 alloy. Extruded plates in the T4 condition were used in the test program. S-N tests in pulsating tension at R = 0.5 were performed on specimens with the weld transverse to the stress direction. Reference tests were made on the base material. Crack growth data were obtained for material in the weld metal, in the HAZ and base material. S-N tests were also made on conventional MIG butt welds from the same batch material to enable a comparison of the two welding methods. The results indicate that the fatigue strength of transverse friction stir welds is approximately 50 percent higher than the fatigue strength of MIG butt welds. The crack growth rates obtained for the weld material were lower than in the base material, probably due to a more fine grained microstructure in the weld region. INTRODUCTION The friction stir welding process has recently been developed as a cost effective alternative to conventional metal inert gas (MIG) and tungsten inert gas (TIG) Transactions on Engineering Sciences vol 8, © 1995 WIT Press, www.witpress.com, ISSN 1743-3533 226 Surface Treatment Effects II welding in aluminum alloys [1]. A major advantage of friction stir welding is that it is a solid state process involving a much lower heat input than that required in conventional arc welding methods. The weld itself and its adjacent narrow heat affected zone both have a very fine-grained microstructure with high mechanical strength. The high tensile strength of the weld material and the favorable geometry would also indicate that friction stir welds could have high levels of fatigue strength. A testing program was implemented to determine the fatigue properties of transverse butt welds of two alloys in the AA6000 series. The data presented in this paper are results from introductory tests on specimens fabricated from extruded plates in AA6082 material in the T4 temper condition. THE FRICTION STIR WELDING PROCESS In friction stir welding the plates to be joined are clamped on a backing plate to prevent movement A cylindrical shouldered tool with a specially profiled pin is rotated at a high speed, see Fig. la. The pin is slowly brought into contact with the joint line, and the material is heated by friction and plasticised in an annular volume around the pin. As the pin is lowered into the plates, soft material is extruded at the surface. Upon further lowering of the pin and movement along the joint line the shoulder face contacts the plate surface and the plasticised material is compressed against the face of the shoulder. The soft material is mashed by the leading face of the pin profile and transported to the trailing face of the pin where it consolidates and cools to form a solid-phase weld. The generation of a friction stir weld has many similarities with extrusion seam welds that form when material is joined in the weld chamber of an extrusion die [2]. The material flow, however, is somewhat different due to the more extensive mechanical mixing of the material from the two plates in the friction stir process. The properties of the weld are closely related to the tool technology. The tool bit shape and material determines the heating, plastic flow and forging pattern. Development of the friction stir welding process has up to now been concentrated mainly on butt and lap joints, however, introductory tests have shown that friction stir welding is suitable for a wide range of joint configurations [4], as shown in Fig. 2. EXPERIMENTAL PROGRAM The specimens were fabricated from AA6082 alloy plate material, in the T4 (as-extruded) condition. The plate thickness was 5 mm. The mechanical properties are listed in Table 1. Transactions on Engineering Sciences vol 8, © 1995 WIT Press, www.witpress.com, ISSN 1743-3533 Surface Treatment Effects II 227 Table 1. Mechanical properties of the AA6082 alloy in T4 temper.

This research study’s the fatigue behaviour of friction stir welded (FSW) and friction stir processed (FSP) joints for joining AA5083-H111 aluminium alloy. The Joining has been implemented on 3mm thickness. Fatigue properties of the welded joints were evaluated based on the superior tensile properties for FSW at 1500 rpm and a feeding speed of 20 mm/min. the FSP was at 1500 rpm and a feeding speed of 40 mm/min. Fatigue alternating bending test was performed at a constant stress amplitude cantilever with fully reversed (R=-1). The fracture surface topography was also analyzed by the aid of an electron microscope. The experimental fatigue properties for base, FSW & FSP welds of AA 5083-H111 aluminium alloy that were obtained from the experimental work showed that all the tested samples of FSP displayed good fatigue behaviour and better fatigue properties near to base material than what the FSW were. The endurance limits were 81 MPa and 71 MPa for FSP and FSW joints respectively and 87 MPa for base metal.

Mechanical surface hardening processes have long been of interest to science and technology. Today, surface modification technologies have reached a new level. One of them is friction stir processing that refines the grain structure of the material to a submicrocrystalline state. Previously, the severe plastic deformation occurring during processing was mainly described from the standpoint of temperature and deformation, because the process is primarily thermomechanical. Modeling of friction stir welding and processing predicted well the heat generation in a quasi-liquid medium. However, the friction stir process takes place in the solid phase, and therefore the mass transfer issues remained unresolved. The present work develops the concept of adhesive-cohesive mass transfer during which the rotating tool entrains the material due to adhesion, builds up a transfer layer due to cohesion, and then leaves it behind. Thus, the transfer layer thickness is a clear criterion for the mass transfer effectiveness. Here we investigate the effect of the load on the transfer layer and analyze it from the viewpoint of the friction coefficient and heat generation. It is shown that the transfer layer thickness increases with increasing load, reaches a maximum, and then decreases. In so doing, the average moment on the tool and the temperature constantly grow, while the friction coefficient decreases. This means that the mass transfer cannot be fully described in terms of temperature and strain. The given load dependence of the transfer layer thickness is explained by an increase in the cohesion forces with increasing load, and then by a decrease in cohesion due to material overheating. The maximum transfer layer thickness is equal to the feed to rotation rate ratio and is observed at the axial load that causes a stress close to the yield point of the material. Additional plasticization of the material resulting from the acoustoplastic effect induced by ultrasonic treatment slightly reduces the transfer layer thickness, but has almost no effect on the moment, friction coefficient, and temperature. The surface roughness of the processed material is found to have a similar load dependence.

The current study aims to provide a comprehensive explanation of metal matrix composite fabrication using various combinations of reinforcements and the principles of friction stir technique, as well as the impact of input processing parameters on mechanical properties performed by various researchers. The researchers sought to establish a link between the parameters of the input process and the output replies. Friction stir welding and processing consumes a lot less energy than other methods. Metal matrix composites have replaced traditional materials in many technical applications due to their unique mechanical and metallurgical qualities, stability, durability, and corrosion resistance. The friction stir method has a significant influence on the mechanical characteristics of manufactured composite surfaces due to process parameters such as rotating speed, tilt angle, feed, and deposition rate. The boost in diverse characteristics in surface composites has been brought forth by the solid-state nature of the processing procedure. Mechanical qualities are also influenced by the pin profile. The most common pin profiles are triangular, cylindrical, hexagonal, and pentagonal. On surface composites, the current work may provide a notion of defect-free welds with greater and enhanced mechanical characteristics.

Due to its excellent energy efficiency and environmental friendliness, friction stir welding (FSW), a very effective solid-state joining process, has been referred to as green technology.It is a method that makes it possible to combine metallic materials, especially lightweight, high-strength aluminum and magnesium alloys that conventional fusion welding had deemed unweldable.As a result, it is regarded as the most critical advance in material joining over the last 20 years.Later, friction stir processing (FSP) was created based on the fundamental ideas of FSW.FSP has been shown to be a reliable and adaptable metalworking process for altering and manufacturing metallic materials.Since FSW/FSP of aluminum alloys has the potential to change the production process in the aerospace, defense, marine, automotive, and railway industries, it has attracted significant scientific and technological interest.It is crucial to optimize the process parameters and comprehensively assess the microstructural changes and mechanical characteristics of the welded/processed samples to promote the use of FSW/FSP technology and assure the structural integrity, safety, and durability of the FSW/FSP components.Thus, this review paper aims to summarize current developments in the mechanical characteristics and microstructural evolution of FSW/FSP aluminum alloys.The mechanism of recrystallization, grain boundary properties, phase transformation, texture evolution, characteristic microstructures, and the impact of these elements on the hardness, tensile and fatigue properties, and superplastic behaviour of FSW/FSP aluminium alloys are all given special consideration.

This paper reports on the employment of the machine learning (ML) techniques, namely support vector machine (SVM), artificial neural networks (ANN), and random forest (RF), for predicting the tensile behavior of friction stir processed (FSP) dissimilar aluminium alloys joints (6083-T651 and 8011-H14). The dissimilar aluminium joints are fabricated using the friction stir welding (FSW) process. After that, the friction-stir welded joints are subjected to the FSP procedure at different combinations of process parameters. The rotational speed, traverse speed, and tilt angle are used as the input parameters, while tensile strength and grain size are used as the output parameters. In addition, three performance characteristics (i.e., coefficient of correlation (CC), mean absolute error (MAE), and root mean square error (RMSE)) are used to check the adequacy of the developed model of ML techniques. It is observed that support vector machine_radial basis function kernel is the most accurate modeling technique for predicting the tensile behavior of processes samples. Furthermore, the optical microscope is also utilized to check the grain size of the nugget zone (NZ) of the weld bead for FSP. It is found that the minimum grain size (i.e., 5.06 µm) is obtained for the FSP sample and this grain size corresponded to the high ultimate tensile strength (UTS). Moreover, the fractographic analysis showed the ductile behavior of FSW and FSP samples.

Magnesium alloys have advantages such as low density, high specific strength and good mechanic damping properties. They are often applied for 3C and transportation industries as structural materials. Magnesium alloys with adding lithium element can make the density lower and the workability better than pure magnesium. A recent report suggested that the second phase α with plank-like shape in extruded dual-phase Mg-Li alloy might be the initial points of fracture under tensile test. In order to redistribute the second phase α, friction stir processing (FSP) followed by stabilization heat treatment is applied for trying to improve the mechanical properties of extruded Mg-9Li-2Al-1Zn alloy (LAZ921-F). This study focus on the effects of distribution of the second phase α on the tensile fracture characteristics and the effects of the ductility change on the roughness of blanking surfaces of Mg-9Li-2Al-1Zn alloy after FSP (LAZ921-FSP) and stabilization heat treatment (LAZ921-FSP-S). According to the shifts of X-ray diffraction peaks, supersaturated solid solution induced by FSP may be eliminated after stabilization heat treatment. Stabilization heat treatment also makes aging time less. The β phase greatly affected by stabilization heat treatment may dominate the changes of tensile mechanical properties of LAZ921-FSP. In the microstructure of FSPed LAZ921 magnesium alloys, there are two kinds of microstructures in SZ. The one is composed of equal-axed α particles. The other is composed of α phase on the grain boundaries of β phase and the α phase is dispersed in the matrix with needle-like shapes. On tensile mechanical properties, the experimental results indicate that LAZ921-FSP has better strength and worse elongation than LAZ921-F. The initial points of fracture in LAZ921-FSP were located on β phase. LAZ921-FSP-S and LAZ921-F have similar tensile mechanical properties and similar initial points of fracture occurred within α phase and α/β interfaces. The AlLi phase and θ phase in heat affected zone (HAZ) may be dissolved into matrix during FSP. Because that the θ phase re-precipitates after stabilization heat treatment and induces greater precipitation hardening effect than that induced by AlLi phase, the hardness of HAZ is higher than other zones affected by FSP. The fractures caused by tensile stress perpendicular to processing direction are on the zones with higher hardness and where hardness difference ocurr. After blanking, there are cracks parallel to extrusion direction found in LAZ921-F. Also, there are cracks induced by blanking found in LAZ921-FSP due to the brittleness of β phase. The quality of blanking surfaces of LAZ921-FSP-S is better than LAZ921-F and LAZ921-FSP because of finer second phase α fined by FSP and better ductility improved by stabilization heat treatment.

Al-Ni in situ surface composites were fabricated by friction stir processing method. Friction stir processing produced a composite with nickel and NiAl3 as reinforcement particles in aluminium matrix. The particles were fine and were in the submicrometer size range. The separation distance between the particles was very small. Impression creep experiments were conducted on the samples both at friction stir zone and base material zone at various temperatures. Steady state creep rates were estimated, and activation energy for creep was calculated. It is observed that the friction stir zone offered a higher creep resistance compared to the base metal zone. Higher creep resistance is attributed to the dissolution of nickel atoms into aluminium matrix and the presence of fine nickel particles and NiAl3 precipitates. The measured activation energy indicated that the associated creep mechanism is the dislocation creep in the temperature range of 30–150°C, both in friction stir zone and base metal zone. At higher temperatures (150–180°C) the diffusion creep mechanism is suggested.

Friction stir processing (FSP) is a surface processing method to modify the microstructure and enhance the mechanical properties of metal surface. This process is also numerated as a method to incorporate second-phase nanoparticles into microstructure and form surface composites. In the current research, the work specimen is vibrated normal to processing line during FSP. Transverse and rotation movements of shoulder are accompanied with vibration motion of specimen. This new process is entitled FSVP (friction stir vibration processing). The effect of FSP and FSVP processes on microstructure and mechanical properties of Al5052 alloy matrix composite incorporated SiC nanoparticles is analyzed. The results show that the presence of vibration during FSP leads to the grain size decrease in the stir zone and it enhances the homogeneity of particle distribution. The results indicate that strength and ductility of friction stir (FS) processed specimens are lower than those processed by FSVP. These are related to increased deformation and strain of soft material in the stir zone as vibration is applied which promotes the dynamic recovery and recrystallization during FSP. The results also imply that the microstructure is refined more and the strength and the hardness of friction stir vibration (FSV) processed specimens increase as vibration frequency enhances.

The properties of metallic alloys can be substantial modified by the addition of a second phase particles. This is especially noticeable when hard particles are incorporated in a relatively soft matrix, often resulting in improved mechanical and tribological performance. This paper presents the results of our study on mechanical and tribological performance enhancement of 6061 Aluminum alloys by incorporation of B4C particle via Friction stir processing (FSP). Unidirectional ball on flat friction and wear tests were conducted with a base material, friction stir processed 6061-Al and 6061-Al doped with B4C particles via FSP against 52100 bearing steel balls under dry sliding conditions. The incorporation of particles not only reduced friction by 30% but also reduced wear by 2 orders of magnitude compared to unprocessed base and FSP material without particles incorporation. FSP alone without particles addition did not have a significant effect on the tribological behavior of the tested aluminum alloy.

Friction stir processing is being used to improve characteristics of advanced manufactured process by improving the strength and ductility of material, joining, surface characteristics, and alloying. In addition, friction stir processing may be used as a first step for recycling metallic waste. The authors are interested in the friction stir processing because they see that friction stir extrusion may be used for producing unique components that could be useful for the development of fuel cells, micromanufacturing, heat exchangers, biomedical applications, and MEMS. The goal of the current project is to develop a custom built friction stir machine in order to investigate multi-scale friction stir extrusion processes. The machine will be used to characterize various friction stir extrusion processes such as forward and backwards extrusion to produce solid cylinders and tubes with outside diameters up to 37-mm down to 3-mm and for tubes with internal diameters down to 2-mm. In addition, various materials will be evaluated for friction stir extrusion processes and the process parameters will be used. The machine described is being implemented in 3 phases. The first phase was the building of the basic machine and perform open-loop tests. The second phase was the implementation of process monitoring and begin to implement closed-loop control. The third phase of building the friction stir machine is to fully implement closed-loop control and begin charactering specific processes. This paper describes the current state of the project (Phase 2). A force transducer, thermocouple, and a displacement transducer are used to monitor the process parameters. A PLC is used to record the process parameters as well as control the 10HP 3-phase 240v ac electric motor that powers the rotating probe. Open-loop tests where the extrusion process was performed manually by the equipment operator were performed where the operators attempted to control forces during the tests and to perform component and system integration tests. A-1100-o aluminum solid billets 12.7mm in diameter were used to produce tubes (OD: 12.7-mm, ID: 6.35-mm). Observations, temperatures, and forces were recorded and are presented. Because this machine was a proof-of-concept machine that is being converted to a production machine, observations made will be used to improve the machine for Phase 3.

The cast Al-Zn-Mg 7000 alloy has become one of the most potential structural materials in many engineering fields such as aircraft body, automotive casting due to their high strength to weight ratio, strong age hardening ability, competitive weight savings, attractive mechanical properties and improvement of thermal properties. The cast aluminium alloy has been modified of surface layer through a solid-state technique is called friction stir process (FSP). But basic principle has been followed by friction stir welding (FSW). This process can be used to locally refine microstructures and eliminate casting defects in selected locations, where mechanical properties improvements can enhance component performance and service life. However, some specified process parameters have adopted during experimental works. Those parameters are tool rotation speed (720 rpm), plate traverse speed (80 mm/min), axial force (15 kN), and tool design (i.e., pin height 3.5 mm and pin diameter 3.0 mm), respectively. The main mechanism behind this process likely to axial force and frictional force acting between the tool shoulder and workpiece results in intense heat generation and plastically soften the process material. The specified ratio of rotational speed (720 rpm) to traverse speed (80 mm/min) is considered 9 as low heat input during FSP and its entails low Zn vaporization problem results as higher fracture toughness of aluminium alloy. It is well known that the stirred zone (SZ) consists of refine equiaxed grains produced due to dynamic recrystallization. FSP has been proven to innovatively enhancing of various properties such as formability, hardness and fracture toughness (32.60 MPa√m). The hardness and fracture toughness of double passes AC+FSP aluminium alloy had been investigated by performing Vicker’s hardness measurement and fracture toughness (KIC)(ASTM E-399 standard) tests. Detailed observations with optical microscopy, Vicker’s hardness measurement, SEM, TEM, and DTA analysis have conducted to analyse microstructure and fracture surfaces of double passes FSP aluminium alloy.

: The microstructures of Al-Mg alloys with greater than 3wt.% Mg can sensitize leaving the material susceptible to intergranular corrosion (IGC); sensitized microstructures are identified by the amassing of phase precipitates at grain boundaries. Friction stir processing (FSP) has previously been shown to increase the corrosion resistance of sensitized Al-Mg alloys through break-up of the continuous network of beta phase particles [1]. In this study, multi-pass FSP is applied to a sensitized 5456-H116 aluminum plate and the resulting microstructure is linked to local mechanical properties (0.2% yield strength, ultimate tensile strength, and elongation) obtained using micro-tensile specimens extracted transversely across the FSP region. In the FSP region, the original sensitized microstructure becomes unsensitized; the unsensitized region is not limited to the friction stir zone but extends outward several mm into the base material. Though the sensitized microstructure is removed, the mechanical testing within the affected area shows the strength and elongation decrease and increase respectively from H116 temper to O temper levels. The previously sensitized microstructure is not observed to have negatively affected the mechanical properties.

Friction stir processing (FSP) has emerged as an advanced solid-state metalworking technique derived from the principles of friction stir welding (FSW). Originally developed for aluminum alloys, FSP enables controlled modification of the near-surface microstructure of metallic components through localized severe plastic deformation, material stirring, and frictional heating. These combined effects promote significant grain refinement, improved homogeneity, and densification within the processed zone, resulting in enhanced mechanical and surface performance. In recent years, FSP has been widely applied to produce ultrafine-grained structures, fabricate surface metal–matrix composites, and support the in situ formation of reinforcing phases, such as intermetallic compounds. Owing to its effectiveness in tailoring surface characteristics, FSP has strong potential for industrial implementation across the aerospace, automotive, marine, and biomedical sectors, particularly in applications requiring wear-resistant surfaces, lightweight structural elements, and high-performance materials. This review highlights recent progress in FSP research and provides insights into current developments and future directions of the technique.

4 - Mechanical properties