Mechanical Properties Of Joints Research Articles

Improved Joint Formation and Ductility during Electron-Beam Welding of Ti6Al4V and Al6082-T6 Dissimilar Alloys

The current work is based on investigating the influence of different technological conditions of electron-beam welding on the microstructure and mechanical properties of joints between Ti6Al4V and Al6082-T6 dissimilar alloys. The plates were in all cases preheated to 300 °C. Different strategies of welding were investigated such as varying the electron-beam current/welding speed ratio (Ib/vw) and applying a beam offset towards the aluminum side. The heat input during the experiments was varied in order to guarantee full penetration of the electron beam. The macrostructure of the samples was studied, and the results indicated that using a high beam power and a high welding speed leads to an increased formation of defects within the structure of the weld seam. Utilizing a lower beam current along with a lower welding speed leads to the stabilization of the electron-beam welding process and thus to the formation of an even weld seam with next to no defects and high ductility. Using this approach gave the highest ultimate tensile strength (UTS) of 165 MPa along with a yield strength (YS) of 80 MPa and an elongation (ε) figure of 18.4%. During the investigation, improved technological conditions of electron-beam welding of Ti6Al4V and Al6082-T6 dissimilar alloys were obtained, and the results were discussed regarding possible practical applications of the suggested approach along with its scientific contribution to developing further strategies for electron-beam welding of other dissimilar alloys. The downsides and the economic effect of the presented method for welding Ti6Al4V and Al6082-T6 were also discussed.

Effect of Femtosecond‐Laser‐Induced Surface Textures on the Microstructure and Mechanical Properties of Mg/Ti Dissimilar Alloys Laser Lap Welds: A Numerical and Experimental Study

The strength of the joints in the Mg/Ti laser welding is difficult to meet the requirement because of the metallurgical incompatibility. This study investigates the influence of microgroove width on the diffusion of molten Mg and the mechanical properties of joints by laser welding Ti6Al4V and AZ31B, employing femtosecond lasers to fabricate microgrooves on the surface of Ti alloys. The optimal contact angle of 56.4° is achieved at the microgroove width of 100 μm because the leading and trailing edges of the microgroove texture can stimulate the formation of the microriveted structure, facilitating the fluidity of the liquid AZ31B. The joint's tensile–shear capability is increased to 2449.9 N, which is 2.8 times stronger compared to joints without microgroove textures, when using a microgroove width of 100 μm and a laser power of 52%. The numerical simulation of the laser welding process was implemented to analyze the temperature field and the fluid characteristics within the melt pool. In the results, it is shown that the microgroove enhanced the material exchange at the interface and accelerated the interfacial reaction, which stimulates the formation of Ti–Al and Mg–Al intermetallic compounds at the central interface of the joint and enhances the Mg/Ti metallurgical bonding.

Study on interfacial healing mechanism of a Ni-Co base dual-phase superalloy during hot-compression bonding

Hot-compression bonding (HCB) as an advanced technique for preparation of large-size homogenized components is widely applied. Despite the fact that interfacial healing mechanisms during HCB have been extensively investigated, the interfacial healing mechanisms in duplex superalloys still need to be clarified. This article investigates effect of deformation temperature on multiple interface (γ′-γ′, γ-γ, γ-γ′) healing mechanism of dual-phase superalloys. The healing mechanism of γ-γ interface at different temperatures involves a necklace-like distribution of discontinuous dynamic recrystallization (DDRX) grains occupying original interface. With increasing deformation temperature, the healing mechanism of γ′-γ′ interface transforms from DDRX to diffusion bonding due to weakening of strain concentration. Simultaneously, as deformation temperature increases, the deformation mechanism of primary γ′ phase transforms from shearing by stacking fault to dislocation pairs. At deformation temperature 1100 °C, the healing mechanism of γ′-γ interface is heterogeneous epitaxial recrystallization (HERX) induced by primary γ′ phase driven by diffusion of Cr element in dislocation pairs. However, as deformation temperature decreases, healing mechanism in γ′-γ interface transforms into DDRX. Although interfacial healing mechanism is transformed at different deformation temperatures, the synergistic action of different recrystallization mechanisms ensures that mechanical properties of joints reached the same level as those of base material.

Mechanical performance of a kind of bolted joint for single-layer latticed shells under pure bending

In this paper, a kind of bolted joint with separated joint-body is creatively proposed. The mechanical properties of the bolted joints in the pure bending state are studied through theoretical calculation, test and finite element simulation. Based on the component method, a simplified mechanical model is proposed. The formulas of the initial rotational stiffness and the yield moment of the joint are derived. For the bolted joints, seven groups of test specimens with different typical parameters are designed. The mechanical performance tests of joints under pure bending are carried out. The influences of the joint-body form and the joint parameters on the mechanical properties of joints are obtained. Finally, the determination methods and the recommended values of the key parameters of the joint are given, which provides a basis for the design of the single-layer latticed shell with new bolted joints.

Investigation on reducing residual stress and optimizing performance of 2219 aluminum alloy friction stir welded joint by cold spraying

In this paper, the cold spraying (CS) was applied on friction stir welded 2219 aluminum alloy joint to reduce its residual stress. The correlation between the process parameters of CS and residual stress and mechanical properties was studied. Results reveal that the grain size of cold sprayed joints is significantly refined comparing to that of the welded joints, meanwhile the content of high angle grain boundaries and recrystallized grains increases. Cu powder has the best effect on enhancing the mechanical properties of joint. With the increase of gas pressure, the residual stress is decreased. The optimal powder type, gas pressure and gas temperature of CS are Cu powder, 3 MPa and 400 °C, respectively. The maximum residual stress is reduced from a tensile stress of 159 MPa in the welded joint to a compressive stress of −17.4 MPa in cold sprayed joint, and the tensile strength and elongation are further increased to 331 MPa and 4.6 %, respectively.

Microstructure and Impact Toughness of Laser-Arc Hybrid Welded Joint of Medium-Thick TC4 Titanium Alloy

This study delves into the impact toughness of medium-thick (12 mm thick) titanium alloy joints crafted through a multi-layer, multi-pass welding technique that blends laser-arc (MIG) hybrid welding technology. Microstructural scrutiny, employing optical microscopy, SEM and TEM, unveils a consistent composition across weld passes, with prevailing α/α′ phases interspersed with some β phase, resulting in basket-weave structures primarily dominated by acicular α′ martensite. However, upper regions exhibit Widmanstatten microstructures, potentially undermining joint toughness. Hardness testing indicates higher values in cosmetic layers (~420 HV) compared to backing layers and bending tests manifest superior toughness in lower joint regions, attributed to smaller grain sizes induced by repetitive welding thermal cycles. Impact toughness assessment unveils diminished values in the weld metal (WM) compared to the heat-affected zone (HAZ) and base material (BM), amounting to 91.3% of the base metal’s absorption energy. This decrement is ascribed to heightened porosity in upper regions and variations in grain size and phase composition due to multi-layer, multi-pass welding. Microstructural analysis proximal to failure sites suggests one mechanism wherein crack propagation is impeded by the β phase at acute crack angles. In essence, this study not only underscores the practicality of laser-MIG hybrid welding for medium-thick TC4 alloy plates but also underscores the reliability of joint mechanical properties.

Welding room development for simultaneous improvement of welder health and weld quality of gas metals arc welded aluminum AA5083-H112

This study investigated the weld joint mechanical properties and welding fume exposure associated with Gas Metal Arc Welding of aluminum AA5083-H112 in 27 different welding room environment conditions. These conditions consist of variation in temperature, as well as intake and exhaust wind velocities. The temperature varies as 19 °C, 27 °C and 35 °C. Both the intake and exhaust velocity vary as 0 m/s, 3.1 m/s and 5.5 m/s. The experimental findings underscore the pronounced influence of these factors on both weld quality and welder exposure to fumes. Notably, intake wind velocity emerges as the most critical factor, contributing significantly to 47.68 % in weld joint tensile strength. The temperature emerges as the least critical factor with 12.02 % of contribution. However, temperature became the most critical factor on weld joint impact energy with 54.89 % of contribution while exhaust wind velocity became the least with 3.89 %. Air quality monitoring highlights the importance of optimal intake and exhaust fan configuration to effectively reduce fume exposure. All examined welding room environment condition are deemed safe for the welder, as they do not exceed the Treshold Limit Value (TLV), except the condition where the welding room lacks of air circulation in intake and exhaust wind velocity of 0 m/s. The identified optimal welding room condition exerts a temperature of 27 °C, intake and exhaust wind velocity of 0 m/s and 3.1 m/s respectively. This condition not only achieves established weld quality standards but also ensures compliance with fume exposure regulation. This research provides valuable insights for optimizing welding room environment to simultaneously maintain weld quality and safeguard the well-being of welders

Improving interface bonding strength of laser-welded steel/CFRTP hybrid joint via bilayer silane film

The γ-aminopropyltrimethoxysilane (γ-APS) and γ-(2,3-epoxypropoxy) propyltrimethoxysilane (γ-GPS) single or bilayer silane film was produced to improve the tensile property of laser-welded 304 stainless steel/CFRTP joint in this work. The bonding mechanism at joint interface was investigated through experiments as well as density functional theory (DFT) calculation. Si-O-Fe covalent bonds were formed between steel and different silane films. Hydrogen bonds were induced at the interfaces of silane coating/polymer sides. The binding energy calculation results suggested that the binding between γ-APS silane coupling agent and steel was more stable than that of γ-GPS and steel. The binding energy of −3.37 eV between amino group in γ-APS and carbonyl group in CFRTP was greater than the binding energy of −4.84 eV between epoxy group in γ-GPS and amide group in CFRTP, which indicated stronger interaction was obtained between γ-GPS and polymer compared to the interaction between γ-APS and polymer. The bilayer silane coating could combine the dominant functional groups of silane monolayer film to obtain stable bonding on both metal side and CFRTP side. Moreover, compared with silane single film, longer silane oligomer molecular chain length was provided by bilayer silane film, resulting in more entanglement sites between silane film and CFRTP and the increased joint mechanical property. The steel/CFRTP hybrid joint reached maximum tensile shear strength of 17.2 MPa, which was further increased by 115.0% and 79.2% than that obtained by γ-APS and γ-GPS silane single coating, respectively.

Novel weld composition to improve mechanical properties of 2219-T8 aluminum alloy joint using double-wire TIG welding

The composition of weld is one of the determining factors for the microstructure and mechanical properties of the joint. In this study, a novel weld composition was designed for 2219-T8 aluminum alloy TIG joint and achieved by Al-Cu and Al-Mg double-wire welding. The relationships between composition, microstructure, and mechanical properties of weld were investigated, and the strengthening mechanisms were discussed. The results show that Al-5.8Cu-0.5Mg was the desired weld composition with defect-free and improved mechanical properties. The microstructure of Al-5.8Cu-0.5Mg weld mainly consisted of rod-shaped α + θ eutectic and nanoprecipitates S phase. Compared with the Al-6.2Cu weld, the yield strength of Al-5.8Cu-0.5Mg weld increased by about 80 MPa, which was the result of precipitation strengthening of S phase. The average tensile strength of the joint with Al-5.8Cu-0.5Mg weld was increased by 25 MPa (about 8.6%) than that of the joint with Al-6.2Cu weld.

Automated structural parameter estimation of semi-rigid complex joints in a benchmark laboratory steel grid by experimental modal analysis

The mechanical properties of joints may impact a system’s static and dynamic behavior. Since connections are usually complex, modeling their geometric details could take time and effort. Thus, joints of structures are often overlooked in model creation and calibration. Therefore, reliable analytical modeling of in-service structures requires accurate and efficient parameter estimation of the connections in their simplified models. However, joints are physically small parts of a system, and parameter estimation techniques may not be sufficiently sensitive to the variations of connections’ mechanical properties. This paper examines the finite element model updating of a laboratory steel grid focusing on the structural parameter estimation of its complex connections using modal data. The mechanical properties of the joints are parametrized by added mass and reduced rigidity. Therefore, several modified models with different combinations of heavier semi-rigid joints are developed. Each model is updated using two modal-based error functions, and the most representative updated model is selected. The results demonstrate how the grid modal outputs are influenced by updating the mass and stiffness of its connections. Moreover, mass and stiffness interactions of the grid joints in the parameter estimation procedure are illustrated. The updated models can efficiently simulate the structural behavior of the grid with increased confidence and reliability.

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.

Analysis of heat generation during friction stir welding of aluminum alloy 2024-T4 and its impact on joint characteristics

Friction stir welding (FSW) is a successful welding technique for joining of aluminium and many other materials with the required joint configurations. During this welding process, large amount of heat is generated, which influences the integrity, performance, and microstructure of the weld joints. In this study, both experimental and numerical approaches are adopted to analyse the influence of heat generation on the metallurgical and mechanical properties of friction stir-welded joints of AA2024-T4. A computational fluid dynamics (CFD) model is constructed for quantitative analysis of heat flux, heat generation, temperature distribution, strain rate and viscosity. The model is validated by experimentally measured temperature data, and both agree well. The results showed that both heat flux and strain rate are more or less symmetric about the tool axis whereas plastic material flow is asymmetric. Heat flux affects the grain size and mechanical properties of the joint.

Impact of heat treatment on mechanical properties of joints during electron beam welding of 2219 alloy

Impact of heat treatment on mechanical properties of joints during electron beam welding of 2219 alloy

Effect of Mo addition on interfacial microstructure and mechanical property of SiC joint brazed by an Ni–Si filler

AbstractNi‐based alloys provide good brazing filler characteristics for the many applications of SiC ceramics. Nevertheless, the presence of graphite is unavoidable in the reaction between Ni and SiC, leading to a significant degradation of the mechanical properties of the joint. This study investigates the effect of Mo in Ni–30Si alloy on the brazing of SiC at 1300°C, to regulate interfacial reactions and reduce residual stresses by decreasing overall coefficient of thermal expansion (CTE) values throughout the brazing process. The addition of Mo up to 8 at.% efficiently suppresses graphite accumulation by converting it into Mo2C + Ni3Mo3C phases and lowering the CTE to 5.4 × 10−6/°C. When the Mo loading exceeds 12 at.%, the interactions between the filler and SiC are reduced as a result of the non‐homogeneous dispersion of Mo. The experimental findings indicate that the joint without graphite has a lap shear strength of 107 MPa, which is nearly three times greater than the joint with graphite. Thermodynamic analyses are performed to provide a comprehensive understanding of the underlying mechanisms responsible for the formation of distinct phases in brazed joints.

Intelligent Prediction of FSW Physical Quantity and Joint Mechanical Properties

Friction stir welding (FSW) process parameters influence welding temperature field and axial force, which affect welding strength. At present, how the FSW process parameters of aluminum alloy 2219-T8 thick plates influence process physical quantity and how the process physical quantity changes the tensile strength about the welded joint are unknown. We focus on the intelligent prediction of FSW temperature, axial force, and mechanical properties, to provide a basis for FSW process control of aluminum alloy 2219-T8 thick plate. Firstly, we conducted the FSW experiment of aluminum alloy 2219-T8 thick plate. Then, we input the welding process parameters, set up a prediction model by particle swarm optimization-back propagation (PSO-BP) neural network to predict the peak temperature and axial force. Finally, we input the peak temperature and axial force, use genetic algorithm-back propagation (GA-BP) neural network to establish a weld tensile strength estimation model, and comply with the prediction of tensile strength.

Analysis of Geometric Parameters on Mechanical Properties of Joints Formed by the Process of Electro-resistance Spot Welding

Analysis of Geometric Parameters on Mechanical Properties of Joints Formed by the Process of Electro-resistance Spot Welding

Investigation on the Microstructure Evolution and Mechanical Properties of High Carbon Steel Friction Welded Joint

In this study, we aim to investigate the microstructure evolution and mechanical properties in friction welded joints of high carbon S45C steel. Thus far, S45C steel was welded with structural steel containing 0.3 wt.%C using friction welding. The microstructures in a friction welded joint were characterized by optical microscopy, scanning electron microscopy, and electron back-scattered diffraction analyses, and then compared to the microstructures of CO<sub>2</sub> arc welded S45C welds. The mechanical properties of joints welded using friction and CO<sub>2</sub> arc welding were evaluated through impact tests and Vickers hardness tests. The microstructural changes, based on the welding process, were analyzed carefully in terms of chemical composition and strain condition in welds. Finally, the relationship between microstructures and mechanical properties in welds was discussed.

Sound dissimilar linear friction welding of A7075-T6 Al and mild steel by simultaneous interfacial deformation using higher forging speed

Sound dissimilar welding of heat-treatable A7075-T6 aluminum and mild steel is extremely difficult due to the formation of interfacial cracks. The present study aims to attempt linear friction welding (LFW) of high-strength A7075-T6 Al alloy and mild steel to obtain sound joints with the highest strength ever by controlling the quality deteriorating phenomena that previous studies have faced. In this study, LFW joints were fabricated under two different applied pressures of 100 MPa and 300 MPa at a forging speed of 5 mm/s, along with various forging speeds ranging from 5 mm/s, 10 mm/s, to 20 mm/s under an applied pressure of 300 MPa, and the joint microstructure, mechanical properties and interface macrostructure were investigated. Furthermore, thermal dependence behaviors of both alloys were systematically investigated to optimize the processing parameters, especially applied pressure during LFW. At lower forging speeds of 5 mm/s and 10 mm/s, the weld defects and un-bonded regions were observed near the center of the weld accompanied by unevenness of butt surface due to the relatively thick intermetallic compound (IMC) formed in the interface which greatly influenced the joint strength. In contrast, at the higher forging speed of 20 mm/s, weld defects at the joint interface were effectively suppressed by promoting the simultaneous and uniform interfacial deformation of both alloys thanks to the extremely thin IMC during LFW. Consequently, a highly efficient joint with 100 % efficiency was successfully obtained at higher forging speed of 20 mm/s and despite the occurrence of softening towards A7075, the fabricated joint displayed a base metal fracture towards the steel side.

Enhanced Toughness and Ductility of Friction Stir Welded SA516 Gr.70 Steel Joint via Post-Welding Annealing.

The SA516 Gr.70 steel possessing excellent toughness and plasticity has been widely used in the cryogenic field. However, the appearance of coarse bainite in the heat affected zone (HAZ) of the fusion welded joint deteriorates the toughness and ductility. In this work, 4.5 mm thick SA516 Gr.70 steel was joined using shielded metal arc welding (SMAW) and friction stir welding (FSW), respectively, and the microstructure and mechanical properties of joints were investigated in detail. The Charpy energy in the HAZ in the FSW joint was 80 J/cm2, which was higher than that of the HAZ in the SMAW joint (60 J/cm2) and due to microstructure refinement. In addition, the total elongation (TE) of the SMAW joint was 17.5%, which was higher than that of the FSW joint (12.1%) and caused by a wider nugget zone with high hardness. The post-welding annealing was used to improve the toughness and ductility of the SMAW and FSW joints, and the microstructure and mechanical properties of the joints after annealing were analyzed. The toughness in the HAZ of the SMAW and FSW joints were 80 and 103 J/cm2, and the TE of the SMAW and FSW joints were 18.6% and 25.2%, respectively. Finally, the as-annealed FSW joints exhibited excellent toughness and ductility. The abovementioned excellent mechanical properties were primarily attributed to the appearance of tempering martensite, decrease in dislocation density, and fine grain.

Inducing low-temperature melting of TiNiCuNb eutectic alloy for manufacturing strong C/C-SiC composite joints

This work designed a novel TiNiCuNb eutectic alloy for manufacturing C/C-SiC composite joints. By introducing Ti into the semi-solid TiNiCuNb alloy, low-temperature melting of this eutectic alloy was induced. Ti/TiNiCuNb/Ti composite interlayers were utilized to join C/C-SiC composite lower than the melting temperature of TiNiCuNb alloy. Effects of joining temperature on the microstructure evolution and mechanical property of joints were investigated. The melting range of this TiNiCuNb alloy was 944 °C to 1064 °C. During the initial melting of the TiNiCuNb alloy, a thin liquid layer formed on the alloy's surface, which provided a path for the rapid diffusion of elements. Without pressure, Ti could be easily introduced into the TiNiCuNb alloy, which induced the complete melting of this alloy at 950 °C. Based on this, we successfully brazed C/C-SiC composite using Ti/TiNiCuNb/Ti interlayers. It not only hindered the formation of brittle compounds in the joints, but also weakened the overreaction between filler and C/C-SiC composite. Due to the high solubility of Si in liquid filler, the joint microstructure was controlled by the interaction between filler and SiC at different temperatures. At 1010 °C for 10 min, the maximum shear strength of 28.5 MPa was obtained. This work contributed to preparing and repairing the C/C-SiC composite.