Increase In Joint Strength Research Articles

The effects of tool rotational speed and post-weld heat treatment of friction stir welded AZ31-B magnesium alloy

Abstract This research article examines the effect of increasing the tool rotational speed and post-weld heat treatment behavior of friction stir-welded AZ31-B magnesium alloy. The variable tool rotational speeds of 1000 rpm, 1200 rpm, 1400 rpm, and 1600 rpm with fixed tool traverse speeds of 30 mm min−1 were chosen based on the trial welding method. Results reveal that the as-welded tensile strength values of 133 MPa, 209 MPa, 215 MPa, and 213 MPa for the corresponding tool rotation speeds and post-weld heat-treated tensile strength values of 140 MPa, 213 MPa, 223 MPa, and 227 MPa significantly increased joint strength when compared to the as-welded process. The measured grain size values are reduced when the tool rotational speed increases due to material dynamic recrystallization. Al-Mg brittle intermetallic compounds significantly reduced the mechanical strength during the increase of the tool’s rotational speed. Fractography analysis reveals all welded samples fractured at the center of the stir zone with a ductile fracture angle of 45°.

Increasing joint strength by achieving carbon fibers’ continuity with ultrasonic assistance during soldering Cf/Al using ZnAl

Ultrasonic assistance was utilized during the soldering of carbon fiber-reinforced aluminum composites (Cf/Al) using ZnAl solder to enhance joint strength. The results indicated that carbon fibers migrated into the joint seam after Al substrate was eroded and the solder was expelled, effectively maintaining the continuity of the carbon fibers. A joint fully reinforced by carbon fibers was achieved with an ultrasonic application time of 60 s. Transmission electron microscopy revealed rapid wetting of the carbon fibers facilitated by ultrasound, characterized by an amorphous/nanocrystalline interface. The maximum joint strength reached 23.5 MPa, which is equivalent to 77.5 % of the Cf/Al.

Effects of concrete strength and joint stirrup ratio on seismic behavior of precast RCS joint with simple detail

Extensive research showed that RC column-steel beam (RCS) joints had sufficient seismic resistance. However, the combination of complicated strengthening details led to more workloads of welding and difficulties in concrete casting. A new RCS joint with whole column-section diaphragm was proposed in this research to address the shortcomings of constructability. The steel web did not pass through the joint, which was convenient for placing the reinforcement and horizontally casting the concrete. Since no additional steel plate was embedded in the joint region, the joint strength was mainly contributed by the concrete and stirrups. This paper aimed to study the effect of concrete strength and joint stirrup ratio on joint behavior. Five interior joint specimens were tested under cyclic loading. Joint shear failure occurred in each specimen. The joint shear strength improved by 88 % when the concrete strength increased from 33 MPa to 63 MPa. Since the joint stirrups had not fully yielded at the peak load point, the joint stirrup had a limited effect on the joint strength, represented by a 10 % increase in joint strength when the joint stirrup ratio changed from 0.5 % to 1.1 %. Nevertheless, the joint stirrups played a crucial role in confining the joint. With the increase of joint stirrup ratio, the growth of joint shear deformation could be restrained and the ductility of the joint would be improved. In addition, the shear strengths of the proposed joints were calculated according to typical methods. The results showed that nearly 90 % of joint strength was contributed by the concrete according to Nishiyama method, while the contribution of concrete represented 60 % to 80 % of total joint strength by using the Chinese specification. Improving the mechanical properties of concrete could effectively enhance the joint behavior. In Chinese specification, the contribution of stirrups may be overestimated since all the stirrups were assumed to reach the yield strength. This research could provide a reference for the future design and application of the proposed joint.

Electrochemical Jet Machining of Surface Texture: Improving the Strength of Hot-Pressure-Welded AA6061-CF/PA66 Joints

Diverse industries are witnessing an increase in demand for hybrid structures of metals and carbon-fiber-reinforced thermoplastic composites (CFRTPs). Welding is an essential technique in the manufacture of metal–CFRTP hybrid structures. However, achieving high-strength metal–CFRTP welded joints faces serious challenges due to the considerable disparities in material characteristics. As an effective method to strengthen metal–CFRTP joints, surface texturing on metal is gaining significant attention. This study introduces an emerging surface texturing approach, electrochemical jet machining (EJM) using a film electrolyte jet, for enhancing the performance of AA6061-CF/PA66 hot-pressure-welded (HPW) joints. Parametric effects on surface morphology and roughness in the EJM of AA6061 are investigated. The results show that a rough surface with multiscale pores can be generated on AA6061 by EJM, and that surface morphology can be modulated by adjusting the applied current density and jet translational speed. Subsequently, the effects of different EJM-textured surface morphologies on the performance of HPW joints are examined. Surface textures created by EJM are demonstrated to significantly enhance the mechanical interlocking effect at the bonding interface between AA6061 and CF/PA66, resulting in a substantial increase in joint strength. The maximum joint strength attained in the present work with EJM texturing is raised by 45.29% compared to the joints without surface texturing. Additionally, the joint strength slightly improves as the roughness of EJM-textured surfaces rises, with the exception of rough surfaces that are textured with a combination of low current density and rapid translational speed. Overall, these findings suggest that EJM texturing using a film jet prior to welding is a potential approach for the manufacture of high-performance metal–CFRTP hybrid structures.

Effect of the Ni plating on Al–Cu dissimilar metal laser welded joint

In this study, the joint strength and interfacial microstructure of Al–Cu laser welded joints are investigated to understand the effect of Ni plating. Cu without plating and Cu plated with 1 μm and 4 μm of Ni were laser welded with Al, respectively, and their differences in joint strength and microstructure were comparatively analyzed. Macrostructure observations showed that the plating had no effect on the change of weld pool shape. Lap shear tests revealed that there was a distinctive improvement in joint strength with the Ni plating. Under a 1.4 kW laser power condition, it was noted that the sample with 4 μm Ni plating showed a 49% increase in load and a 100% increase in elongation compared to the sample without plating. Fracture surface observations revealed that Ni addition has changed the crack propagation path resulting in the increased joint strength. Microstructural analysis showed that the Ni is occupied in intermetallic compounds (IMCs) such as Al3Cu2, AlCu, and Al2Cu3 developed at the interface between Cu and Al2Cu which were known as the primary crack propagation phase in Al–Cu laser welded joint. Additionally, increases in their thickness and changes in their shapes to irregular wavy forms were observed, potentially reducing load concentration and increasing joint surface area, facilitating stable joint formation. Density functional theory calculations showed that the IMCs with Ni undergo contraction in the cell volume suggesting solid solution strengthening of IMCs by Ni addition.

The influence of combination of surface roughness and nanostructure of adhesive on the strength of adhesively bonded joints

Nowadays, adhesively bonded joints are frequently employed in engineering designs as they enable the manufacture of joints with great strength while remaining light. These joints used in aviation sectors, where lightness and reliability are important, are generally designed to join metal-metal, metal-composite and composite-composite adherends. The surface roughness of the adherends with its degree and the way the adhesive interacts with the surface are the most crucial parameters in these applications. In the current work, surface roughness and normal stress strength of nano-composite adhesive in butt joint subjected to tensile loading were investigated. DP460 liquid structural epoxy from 3 M was used as adhesive, AA2024-T3 aluminum alloy as adherend, Graphene-COOH and Carbon Nanotube-COOH as nanostructures while sandpaper and sandblasting methods were used for introducing roughness to the adherend surfaces. A two dimensional axisymmetric FE model was developed to get an insight about the joint failure. When the failure load obtained from experiments was examined, an increasing trend in maximum force values was noticed with an increase in surface roughness, but this increase in joint strength decreased when the surface roughness increased to very high values. In addition, minimum surface roughness reduces the adhesive's adhesion to the surface, thus reducing the normal stress strength of the joint. When 1 % Graphene-COOH nanostructure was added to the adhesive, the ultimate normal stress of the joints increased from 9 % to 21 %. However, when the same percentage of Carbon Nanotube-COOH was added, the increase was from 27 % to 62 %. Different normal stress values of the joints were obtained using by sanding and sandblasting methods even though the roughness resulting from the two treatments was similar.

Evolution of microstructure and mechanical properties of GTAW joint for magnesium alloy thin plate by post-weld reinforcement compression treatment

Gas tungsten arc welding (GTAW) joints of magnesium alloy thin plates generally exhibit low welding coefficients. Therefore, post-weld reinforcement compression treatment is utilized to improve mechanical properties of the joints in this experiment. The study shows that the grain shapes and sizes in various zones of the treated welded joints alter significantly, and the presence of twins is also detected especially in the base material (BM) and heat-affected zone (HAZ). The strength of the welded joints progressively rises with the increase in the compression reduction. The welding coefficient of the C3-joint reaches 91.6% when the compression reduction is 1 mm. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) are 271 MPa,173 MPa and 7.2% respectively. The post-weld reinforcement compression treatment introduces abundant dislocations in the fusion zone (FZ), contributing significantly to the increase in joint strength. In addition, solid solution strengthening and texture strengthening also exert a role.

Simultaneous reduction in laser welding energy consumption and strength improvement of aluminum alloy joint by addition of trace carbon nanotubes

The widespread use of laser welded aluminum alloys in industrial production offers potential benefits to sustainable development and socio-economic progress. It simultaneously enhances the weld strength while reduces the energy consumption. Despite the promise of these alloys, research on reducing their energy consumption during laser welding is lacking. In this study, a dual effect of enhancing joint strength in 2A12 aluminum alloy and reducing energy consumption is achieved by the addition of trace carbon nanotubes (CNTs). The “welding efficiency" is defined and an energy consumption model for laser welding of aluminum alloys is developed. Next, the laser welding process with the addition of trace CNTs (LC) and the single laser welding process (LW) were compared and analyzed. The results indicate that adding trace CNTs can reduce energy consumption by more than 33 % and increase joint strength by 101 MPa. Furthermore, it is found that the LC process offers significant energy-saving advantages over other laser welding of aluminum alloy processes described in previous studies. These improvements is attributed to the increased laser absorption by the aluminum alloy induced by trace CNTs, as well as their residual presence in the joint, which acts as a strengthening medium. This work provides new insights and presents a novel approach for achieving low-carbon, high-quality welding of aluminum alloys.

Durability of Single Lap Friction Stir Welded Joints between S355-J0 Steel and AA5083 Aluminum Alloy–Mechanical Tests

This study aims to investigate a friction stir welded joint between steel and aluminum alloy. FSW is nowadays one of the most interesting joining techniques due to the possibility of connecting materials and thicknesses that are difficult or impossible to weld with traditional techniques. The main advantage is that materials are not affected by thermal cycle problems during solidification and cooling, and the absence of fumes and pollution during the process favors the quality of the welded joint. The life of metal joints could be greatly reduced in a corrosive environment since the less noble material will tend to increase its corrosion rate, while the nobler one will reduce its electrochemical dissolution. Accelerated aging tests (i.e., salt fog test) are used to estimate the lifetime of metal joints in highly aggressive environments. The aim of the present work is to evaluate the durability at a long aging time in the salt spray test (according to ASTM B117) of carbon steel/aluminum alloy joints, obtained by FSW. In this first part, mechanical test results are reported. A deep metallographic and chemical investigation is going to be reported in part two. The current research work investigates the welding direction and residence time in the salt spray chamber. The breakage of all tested samples, evaluated after the tensile tests were carried out, always occurs at the interface of the joint, regardless of the change of direction of the weld on the advancing or retreating side. The welding direction influences the breakage of the joint only before the aging treatment. Specifically, specimens produced in advance are characterized by increased joint strength. On the other hand, the factor that influences the performance of the joints is the exposure time where, starting from the first point of aging, i.e., after two months, there is a decrease in the maximum load of 40%, and the effect of corrosion leads to a significant deterioration of the weld which remains almost similar until the last point of aging.

Modeling failure and instability of a single-jointed rock column based on finite deformation theory

The mechanical behaviour of rock columns is closely tied to factors such as joint development and height-to-width (H/W) ratio. Based on a recently developed finite deformation analysis scheme that can consider both material failure and structural instability of rock columns, uniaxial compression numerical tests of different H/W ratio rock columns containing a single-filled joint were carried out. It analyzes the effects of the strength of joint-filled material (joint strength) and H/W ratio on strength characteristics and failure modes of rock columns. The numerical results indicate that the joint strength controls the joint failure degree, macro-strength, stress distribution, and failure zone range of the rock column. Under different H/W ratios, the macro-strength of the rock column increases in an S-shaped curve with the increase in joint strength. Lower joint strength will accelerate joint failure, resulting in the failure mode of the rock column being joint failure-induced structural instability. As the joint strength and H/W ratio increase, the failure mode of the rock column evolves into the mode of cooperative material-structure-induced collapse and finally develops into structural instability-induced material failure. The research results have a particular reference significance for selecting grout materials for columnar jointed rock mass engineering.

Experimental and numerical assessment of thermomechanical and morphological characteristics of pin and pinless micro friction stir welds

In the realm of micro-Friction Stir Welding (FSW), distinct challenges arise compared to conventional FSW, encompassing faster heat dissipation through the backing surface, and higher impact of hooks on joint performance due to the reduced effective sheet thickness. Given the limited variability in tool design in micro-FSW, this study delves into the influence of pinless tool in comparison to pin tool on hook formation, temperature evolution, and bonding mechanisms. By conducting a combination of experiments and numerical investigations on 0.5 mm lap FSW joints, the study unveils that pin tool, with an 11% higher peak temperature and 46% greater effective sheet thickness, achieved 4% increase in joint strength with 26% lesser axial force during traversing. Pin tool exhibited a 10–11% higher proportion of recrystallized grains, with 11.1% and 57.6% grain refinement in the weld centre and hook regions, respectively, primarily due to pin-assisted material stirring. In contrast, pinless tool exhibited a flat nugget with directional grain growth toward the weld bottom. The pin weld demonstrated nearly three times the maximum equivalent plastic strain compared to the pinless weld, confirming the intense movement of plasticized material in the vicinity of the pin and effective intermixing across the sheet-interface.

Influence of tool geometry on reaction forces and strength of an inseparable joint produced on a prototype stand with the use of jaws

The present article describes a new and innovative method of producing an inseparable joint with the use of expansion jaws. The effect of jaw tool geometry on the reaction forces and ultimate strength of an inseparable joint formed on a prototype stand was analyzed. The results are also compared of joints produced by jaws with single movement method and with complex movement method. The tool responds with bending and pressing one part into the other, which results in their permanent connection. In the tests, differentiation was introduced with regard to the height of the applied force to the collar of the connection pipe. A novelty is also a solution based on a complex, parameterized trajectory of the stamp movement consisting of horizontal and vertical displacements. This paper presents the tests of the joints formed at the stand. The new approach described in this article has resulted in a joint strength increase of approximately 30% using the innovative complex jaw movement of the biaxial clinching process. A joint tensile strength close to 1000 N was achieved.

Real-time temperature monitoring of weld interface using a digital twin approach

A new friction processing technique is developed for lap welding of Al–Cu sheets using inter diffusion of copper and aluminium at their interface. The metals selectively melt at the interface at a temperature near their eutectic point. This paper proposes a digital twin approach for real-time temperature monitoring at the joint interface using the machine’s real-time current data. The real time temperature data is used to predict exact instance of interface melting and to control the resulting weld microstructure. The digital twin model is calibrated using a finite element model which is in turn calibrated using experiments. Moving average of machine current and temperature history are used to predict real time interface temperature using a linear regression based recursive machine learning model with high precision. The model predictions have an R2 value of 99.5%. The digital twin approach resulted in significant increase in joint strength and fracture energy.

Implementation of Family Nursing Care for Clients with Rheumatoid Arthritis to Physical Mobility Disorders with Active and Passive Movement Exercises

Background: Rheumatoid Arthritis (RA) is a disease characterized by a chronic autoimmune inflammatory disorder or autoimmune response that causes weakening of the joints and synovial lining, especially in the hands, feet, and knees. Patients with RA often experience impaired physical mobility, a condition where a person cannot move freely due to conditions that hinder movement (activity). One of the interventions that can be given to RA patients is Range of motion (ROM) exercises, which are exercises performed to maintain or improve the perfection of the ability to move joints normally and completely to increase muscle mass and muscle tone. research to assess the effectiveness of implementing family nursing care with active and passive movement exercises against impaired physical mobility in Rheumatoid Arthritis sufferers in the work area of Taba Health Center, Lubuklinggau City, in 2022. Methods: This study uses a qualitative design with a case study approach to describe information descriptively. In-depth and explores nursing problems for families with rheumatoid arthritis with impaired physical mobility due to joint stiffness. Results: After implementation by giving active and passive motion exercises to both subjects (Mr. S and Mrs. E) for five consecutive days with a time of 10-15 minutes, both subjects said that stiffness in the extremities was reduced and the value of muscle strength increased to 5 and 4. Conclusion: Implementing nursing care with active and passive motion exercises can increase joint strength in clients with rheumatoid arthritis.

Vacuum diffusion bonding between equiatomic CoCrNi-based concentrated solid solution alloys system and 316 stainless steel by spark plasma sintering

Spark plasma sintering (SPS) is a new method for diffusion bonding of dissimilar metals. In this study, equiatomic CoCrNi-based concentrated solid solution alloys (CSSAs) system (CoCrFeNiMn, CoCrFeNi, and CoCrNi) were successfully joined to 316 stainless steels by SPS diffusion bonding, and the effect of bonding temperature and concentration on diffusion behavior and tensile property of bonded joints were investigated. The tensile strength of the CSSAs/316SS joints were gradually increased with increasing bonding temperature. In addition, the tensile strength of the joints bonded at 0.8Tm were all exceeded 80% of that in 316SS. Meanwhile, the bonding at 0.8Tm seemed to have sufficient diffusion and grain growth at the interface, resulted in the disappearance of voids and the increase in strength of joint. In CoCrNi/316SS joint, large element concentration variation would amplitude in the diffusion zone, could result in rapid diffusion of atoms and large diffusion distance. The diffusion distance of diffusion zone in the CoCrNi/SS joint was increased by nearly two times compared to traditional diffusion bonding. Furthermore, it suggests that the continuous FCC solid solution structure was generated in the diffusion zone, which was beneficial to the increase of tensile property in joints. The tensile strength and elongation of diffusion bonded CSSAs/316SS joints were increased compared to laser beam welded joints.

Enhancing welding strength of thermoplastic vulcanizate/aluminum alloy via adding zinc methacrylate

Welding of metals and polymer materials has always been one of the difficult problems. In this work, we incorporated zinc methacrylate (ZDMA) to polypropylene/ethylene propylene diene rubber thermoplastic vulcanizate (PP/EPDM TPV) to improve the welding performance of the TPV and A6061-t6 aluminum alloy (6061). We firstly processed a welding simulation experiment on a flat vulcanizer. In the experiment of simulating heat source, ZDMA effectively improved the strength of TPV/6061 joints, and the strength of the joints with 30 phr (parts per hundreds of rubber) ZDMA increased tenfold compared to that with 5 phr ZDMA. The increase of joint strength was the result of the combined effect of TPV's polarity, dimensional stability, and interfacial chemical bonds. The results of X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) showed that: during the welding process, the carboxylate ions (-COO-) of ZDMA in TPV migrated to the interface of TPV/6061 joints and constructed chemical bonds (C–O–Al) with 6061. Then, we welded the TPV and 6061 using a Friction Stir Spot Welding (FSSW) machine, the strong interface strength (tension-shear load = 1.2 kN) between TPV and 6061 verified our simulation experiment. Furthermore, the knowledge in this work will benefit the research in welding of TPV and lightweight metals to improve the strength of the interface between plastics and metals.

Influence of carbon and glass fiber reinforced composite adhesive on the strength of adhesively bonded joints

Abstract Today, due to the frequent use of composite materials used in the aerospace and automotive industries, an intensive study is carried out on the joining methods of these materials. One method of joining composite or aluminum alloy materials is adhesive bonding. Studies on the development of the strengths of adhesively bonded joints focused on adhesive type, the bonding method, and hybrid joints. In the present study, a different method was used to increase joint strength. This study experimentally and numerically investigated the mechanical properties of single-lap joints bonded by a composite adhesive – obtained by adding fiber fabric to the adhesive. Adhesively bonded single-lap joints were produced using DP460 toughened adhesive type as the adhesives; AA2024-T3 aluminum alloy was used as the adherend, and carbon fiber and glass fiber fabric were used as the added fiber. In addition, for the numerical analysis of the presented study, the bulk properties of the composite adhesives were obtained. As a result, the use of fiber-reinforced adhesive in bonding joints significantly increases the failure load of the joint, as it prevents the progression of cracks formed in the joint. However, the increase rate in the failure load changes depending on the adhesive thickness and the type of fiber fabric. As follows, the failure loads of the fiber-reinforced joints increase between 5% and 41% compared to the non-fiber-reinforced joints. In addition, it was observed that the results obtained from the numerical analysis and the results obtained from the experiments were consistent with each other.

Nonlinear finite element investigations on different configurations of exterior beam-column connections with different concrete strengths in column and floor

The fast development of quality concrete production has increased the usage of high-strength concrete (HSC) in the columns of high-rise buildings where high axial column loads exist. In contrast, normal-strength concrete (NSC) is used in the floor system for economic reasons. This produces a weak concrete zone at the intersection of columns and floors. Studies focused on evaluating the performance of such connections are still limited. The current numerical study investigates the performance of such connections. The developed numerical model has been verified against the experimental test for connections with different column-to-beam strengths. The numerical model has demonstrated acceptable accuracy compared to the experimental results. Moreover, the validated model has been employed to investigate the influence of different column-to-floor strengths on connections with and without transverse beams and floor slabs. It has been found that the strength and stiffness of connections with different concrete strengths have been improved compared to monolithic connections. Furthermore, the increase in joint strength and stiffness for connections with different column-to-floor strengths is more pronounced for connections with transverse beams and floor slabs due to their contribution to achieving proper confinement conditions for the weak concrete in the joint zone. In addition, the presence of a transverse beam affects the induced stress of the beam bars, resulting in a change in the mode of failure to beam flexural failure, whereas the presence of a slab floor increases both the stiffness and flexural strength of the beam. However, connections with the floor slab suffered high damage due to the transferred equilibrium torsion. Moreover, connections with different column-to-floor strengths exhibited larger stains in their joint stirrups; hence, additional joint stirrups are recommended to avoid the brittle shear failure of the joint. The study ended by evaluating the response of such connections under high axial column loads. It has been observed that planer connections perform poorly in terms of strength and ductility, while adequate performance has been observed for connections with transverse beams or slabs. Therefore, the role of the transverse beam and slab should be taken into account in the design of the connections with different column-to-floor strengths.

Effects of adherend notching on the bonding performance of composite single-lap joints

The use of adhesively bonded joint is a mainstream and effective approach for solving connection problems of composite materials. Single-lap joint (SLJ) is one of the most frequently used joint types in the industry due to its simple geometry and easy applicability. The main factors in designing SLJ are the notch geometrical configurations (depths and lengths), the bond overlap lengths, and the types of adhesives. However, the influence of the notch geometrical configurations (depths and lengths) on joint bonding performances under different adhesive types (brittle and ductile adhesives) is still not fully understood. In this study, both the un-notched and notched 2D finite element models of SLJs have been developed and verified by comparison with literature-reported data and self-performed experiments, respectively. Subsequently, this validated 2D modeling approach is used to evaluate the influence of notch geometrical configurations and overlap lengths on the SLJs bonding performances in terms of failure loads, peel stresses and shear stresses distributions under two different brittle and ductile adhesives. In addition, a three-point bending resistance numerical analysis of SLJs has been carried out to investigate their flexural properties. The research conclusions will serve as a guide for the SLJs to choose proper adhesive types and notching configurations to increase joint strength and decrease stress concentrations.

Effect of post-weld heat treatments on the microstructure and mechanical properties of underwater friction stir welded joints of 7003-T4/6060-T4 aluminium alloys

To further improve the mechanical properties of underwater friction stir welded joints of 7003/6060 aluminium alloys, post-weld heat treatment (PWHT) was carried out. The results show that the combination of water-cooling and PWHT is an efficient method to greatly improve the strength of the dissimilar joints. Through solution heat treatment followed by artificial aging (STA), the largest ultimate tensile strength (UTS) of the dissimilar joint can reach 254.0 MPa, which is equal to the UTS of 6060-T6, and the elongation of the joint is 12.7%. The improvement in strength is attributed to reprecipitation of the high density of the β'' phase. For direct artificial aging (AA) after welding, the largest UTS (218.9 MPa) is obtained when aged at 175 °C for 8 h. Although the pre-existing β′ phase grows coarse to some extent, GP zones and the β'' phase are reprecipitated during AA, which leads to a great increase in joint strength compared with the as-welded samples. However, the elongation severely deteriorates to 4.4% due to strain localization caused by the decreasing width of the soft region. Abnormal grain growth (AGG) takes place in the stir zone (SZ) of all joints subjected to STA, while equiaxed grains with limited growth are retained in joints subjected to AA. Compared with the distribution of precipitation phases, the grain size plays a minor role in the mechanical properties of the dissimilar joints.