Mechanical Properties Of Joints Research Articles

Multi-pass butt welding of thick TA5 titanium-alloy plates by MIG: Microstructure and Properties

A 35 mm-thick sheet of TA5 titanium alloy was successfully joined by metal inert-gas (MIG) welding. The welded joints were analyzed in a more integrated and comprehensive manner. The joint microstructure was analyzed by OM, SEM, EBSD, and TEM. Mechanical properties were analyzed by tensile, impact, and microhardness tests. The corrosion resistance of the joints was determined by FeCl3 immersion corrosion. Experimental results showed that the mechanical properties and corrosion resistance of the fusion zone (FZ) were poorer than those of the base material (BM). The mechanical properties of the welded joints were related to the acicular grains in the FZ. The 260A joints showed relatively good mechanical properties. With increased welding current, the proportion and size of the acicular grains increased, and the strength of the joint increased, but the plastic toughness decreased. When the welding current was too small, anisotropy occurred in the FZmiddle, which affected the mechanical properties of the joints. The corrosion resistance of the FZ was lower than that of the BM, and the corrosion resistance of the three groups of joints decreased in the order 300A > 230A > 260A.The welding current affected the corrosion resistance of the FZ by influencing the grain size of the FZ, the frequency of the HAGBs, and the GND density.

Effect of process parameters on joint quality and mechanical properties of local-thickened self-piercing riveted steel and die-casting aluminum joints

Effect of process parameters on joint quality and mechanical properties of local-thickened self-piercing riveted steel and die-casting aluminum joints

Role of Cr addition in Ni-based interlayer on strengthening titanium and steel dissimilar bimetallic structures enabled by directed energy deposition with laser beam

For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam (DED-LB), pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work. Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically. The distribution of intermetallic compounds (IMCs) such as β-Ti, Ti2Ni, TiNiFe0.2, Ti2Ni3Si and TiB2 in joints was revealed. The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely. Notably, additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus, leading to fewer IMCs in joints. As a result, both bonding strength and toughness of joints were remarkably improved. The findings emphasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.

Investigation of interfacial microstructure and connection mechanism of magnetic field-assisted magnesium/aluminum laser welding joint

Variable process experiments to prepare hybrid joints of AZ31 magnesium (Mg) and 6061 aluminum (Al) alloys by magnetic field-assisted laser welding were performed in an overlap Mg-on-Al configuration with the addition of titanium (Ti) foil. Temperature field and flow field of molten pool including chemical potential of each element were also calculated. It is shown that at the optimal welding parameters, the shear force of joint reaches 887.79 N, which is 83.4 % higher than that of no-added joint. In the case of external magnetic field, the improved mechanical properties of joints largely depend on the diffusional barrier effect of Ti foil, which benefits from the enhanced energy absorption and flow of molten pool leading to the enlargement of interface connection area and the formation of Ti-Al compounds such as TiAl3 at Mg/Al interface. Meanwhile, the grains refines due to the magnetic field, which reduces the strain at the joint and enhances the uniformity of the interface microstructure. However, under the condition of excessive magnetic field strength, the enhanced stirring effect of molten pool will cause Ti foil break and the direct interaction between Mg and Al, which deteriorates the joint properties.

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 1mm. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) are 271MPa,173MPa 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.

Investigation of the effects of beam oscillations in electron beam–welded S1100M TMCP steel

The development of thermomechanically controlled processed (TMCP) high-strength steel (HSS) has significantly contributed to designing and developing the intricate structural components. It has broader applications in the cranes and lifting process industry (base frame, crane jibs, and crane columns), trailers, agricultural and forestry machinery, earth-moving equipment, etc. However, the development of new-grade steels with higher tensile strength led to higher requirements for welded joints, and the associated weldability issues have inspired detailed studies on electron beam welding (EBW) with different beam oscillations. Beam oscillation application with EBW processes improves the welding efficiency, weld quality, weld geometry, keyhole, etc., affecting the welded joints mechanical and microstructural properties. Thus, the present study investigates the impact and comparison of various beam oscillations on the microstructural and mechanical properties of EB-welded S1100M steel. The influence of welding parameters on the microstructure of welded joints was analyzed using a scanning electron microscope (SEM) and electron backscattered diffraction (EBSD). The analysis focused on evaluation of grain sizes, morphologies, distributions, and crystallographic orientations of different phase constituents in fusion zone (FZ) and heat-affected zone (HAZ). The mechanical properties were analyzed using hardness, tensile, and Charpy V-notch impact tests. The texture in the FZ is typically random, while the HAZ typically exhibits a strong rolling texture. In general, the cooling rate in EBW is very fast, possibly resulting in a fine-grained structure and reduced formation of coarse second-phase particles in the weld zone. The elliptical beam oscillation showed the highest hardness in HAZ 450 HV10. Elliptical beam oscillation slightly improves the welded joint’s tensile strength, and the impact test showed mixed fracture behavior.

Особливості електронно-променевого зварювання магістральних трубопроводів з титанового сплаву

Titanium alloys have high strength and satisfactory weldability. They are widely used in the production of aircrafts and other structural elements in the modern aerospace industry. However, due to a high requirement for aviation and rocket-space technology, increasing the reliability and durability of responsible purpose remains an urgent issue. In this study, the results of welding tubular billets with an electron beam are presented. The subject of this article is the features of tubular billets made of complex titanium alloy electron beam welding. The purpose of this work is to ensure that welds of tubular work pieces have a high level of mechanical properties, based on the welding modes experimental testing results. To achieve this goal, the following tasks were set up and solved in this work: to investigate the mechanism of pore formation in welded joints; to study the effect of electron beam welding on the properties of the weld; ensure high indicators of physical and welded joints mechanical properties. The following research results were obtained. It was possible to obtain satisfactory characteristics of the welded joint by welding in the lower position on the substrate and in the horizontal position. The use of heat treatment increases the strength of welded joints to the level of the base metal. Welded seams, regardless of the welding method, have a coarse-grained structure with liquefaction heterogeneity, which is manifested in uneven etching of the seam. Conclusions: Various metallurgical aspects of titanium electron beam welding were studied. During electron beam welding of tubular blanks, pores are formed mainly near the fusion zone and in the seam axis. Edge mechanical processing, speed reduction, work piece rotation, and welded metal remelting dramatically reduce the number of pores in seams welded in the lower position. Crater removal with a stationary work piece avoids root defect formation in the area of annular seam closure. The obtained results have scientific and practical value in the welded joints of tubular blanks mechanical properties improvement.

Microstructural Characteristics and Properties of Laser-Welded Diamond Saw Blade with 30CrMo Steel.

In order to enhance the quality of diamond composite materials, this work employs a Cu-Co-Fe and Ni-Cr-Cu pre-alloyed powder mixture as a transition layer, and utilizes laser-welding technology for saw blade fabrication. By adjusting the laser-welding process parameters, including welding speed and welding power, well-formed welded joints were achieved, and the microstructure and mechanical properties of the welded joints were investigated. The results demonstrate that the best welding performance was achieved at a laser power of 1600 W and a welding speed of 1400 mm/min, with a remarkable tooth engagement strength of up to 819 MPa. The fusion zone can be divided into rich Cu phase and rich Fe phase regions, characterized by coarse grains without apparent preferred orientation. The microstructure of the heat-affected zone primarily consists of high-hardness brittle quenched needle-like martensite, exhibiting a sharp increase in microhardness up to 550 HV. Fracture occurred at the boundary between the fusion zone and the heat-affected zone of the base material, where stress concentration was observed. By adjusting the welding parameters and transition layer materials, the mechanical properties of the joints were improved, thereby achieving a reliable connection between diamond composite materials and the metal substrate.

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.

Thermal and Mechanical Investigation of Friction Stir Welding with Disparate Materials AA6061 and AA7075

Background:: The primary objective of this study is to assess the impact of welding conditions on the mechanical properties of friction stir-welded butt joints created from two distinct aluminium alloys, namely, AA6061 and AA7075. Friction stir welding (FSW), known for its innovation and low-energy solid-state bonding technique, was employed in this research. Methods:: FSW experiments were carried out on both AA6061 and AA7075 alloys using a computer numerical control (CNC) machine. The selection and design of the tool geometry were meticulous, with an emphasis on new pin profiles that are nearly flat at the weld contact point. Precisely, four distinct tool geometries were machined from HC-HCr (High carbon, high chromium steel): Circular, Square, Tapered third, and Triangular. Critical process variables that significantly influence weld quality include rotation speed (800 rpm-1400 rpm) and traverse speed (12 to 25 mm/min). These variables were carefully optimized to achieve flawless welds. During the friction stir welding process, the nugget zone undergoes significant deformation, leading to the formation of a new microstructure that substantially impacts the mechanical properties of the joint. Results:: This study comprehensively investigates the thermal and mechanical properties of friction stir welding using aluminium alloys AA6061 and AA7075, considering various tool shapes. Among the four tool shapes employed, two were found to yield higher hardness values (referred to as BH). Notably, the square-shaped tool produced the highest temperature, reaching up to 690ºC, as determined by thermocouple readings. Based on the findings, the optimal FSW parameters for enhancing hardness involve an axial feed and spindle speed of 800 rpm combined with a feed rate of 15 mm/min. These parameters were identified as crucial for achieving the desired mechanical properties in the friction stir-welded joints. Conclusion:: This study presents new developments in FSW technology, which may have patent implications.

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.