Mechanical Properties Of Joints Research Articles

Interfacial microstructural characterization and mechanical properties of inertia friction welding of 2219 aluminum alloy to 304 stainless steel

Aluminum alloy/steel hybrid components are receiving more and more attention in recent years due to their great potential in reducing weight while maintaining the mechanical properties of the structure. Inertia friction welding was performed to join 2219 aluminum alloy (Al alloy) bar to 304 stainless steel bar. The effects of welding parameters on the evolution of intermetallic compounds (IMCs) and tensile strength of the joints were investigated. High-quality welded joints can be obtained at the parameters combination of the medium friction pressure (120 MPa) and low rotational speed (1100 rpm) from the experimental study. Microstructural analyses indicated that the enrichment of Cu element at the friction interface formed Al2Cu IMCs instead of Fe-Al IMCs, which was usually reported to exist at the Al alloy/steel friction welded interface. The formation of the Al2Cu IMCs layer was mainly attributed to the accumulation of Al2Cu (precipitate in 2219 Al alloy base metal) at the wavy surface of the steel, significantly promoting the growth of Al2Cu by the subsequent precipitation process. However, cracks could easily occur in a thicker Al2Cu IMCs layer at a high heat input, which seriously deteriorated the mechanical properties of joints. Therefore, the massive formation of the Al2Cu IMCs layer should be suppressed by controlling the welding parameters to avoid any internal cracks at the weld interface.

Research on Parameters of Wire-Filling Laser Welding and Quenching Process for Joints Microstructure and Mechanical Property of BR1500HS Steel

With the aim to investigate the effect of parameters and the quenching process on the joint microstructure and mechanical properties of hot stamping steel by laser welding, BR1500HS boron steel was welded by wire-filling laser welding with ER70-G welding wire under different parameters. The welded specimens were heated to 900 °C and held for 5 min before water quenching. A universal material test machine, optical microscope, Vickers hardness tester, scanning electron microscope, and electron backscatter diffraction (EBSD) were used to characterize. The results show that the heat input should be greater than 1040 J/cm and the optimal wire-feeding speed is between 160 cm/min and 180 cm/min. The tensile strength of the quenched joint can reach greater than 1601.9 MPa at compatible parameters. More retained austenite distributes in the fusion zone (FZ) and fine grain zone (FGZ) than the coarse grain zone (CGZ) before quenching. However, the retained austenite in FZ and heat-affected zone (HAZ) decreases clearly and distributes uniformly after quenching. The grain diameter in FZ before quenching is not uniform and there are some coarse grains with the diameter greater than 40 μm. After quenching, the grains are refined and grain diameter is more uniform in the joint. With the increase in heat input, the microhardness of FZ and HAZ before quenching decreases from 500 HV to 450 HV. However, if the wire-feeding speed increases, the microhardness of FZ and HAZ before quenching increases from 450 HV to 500 HV. After quenching, the joint microhardness of all samples is between 450 HV and 550 HV. The fracture morphology of the joint before quenching consists of a large number of dimples and little river patterns. After quenching, the fracture morphology consists of a large amount of river patterns and cleavage facets due to the generation of martensite.

Microstructural characterization and mechanical properties of TIG weld joint made by forged Ti–4Al–2V alloy

The weld of titanium alloy promotes the complex components to be widely utilized in various fields. It is necessary to investigate the microstructure and mechanical properties to ensure the reliability of weld joint. In the present study, the microstructure, texture and mechanical properties of a joint made of the near-α titanium alloy Ti–4Al–2V, prepared by multi-layer and multi-pass TIG welding process, were investigated. The results show that the heat affected zone (HAZ) and fusion zone (FZ) are composed of α′ martensite, acicular α and lath like widmanstätten α + β, which is complex than that of the base metal (BM). Meanwhile, the texture in HAZ and FZ, including {0001} <11–20> plate texture, {11–20} <10-10> plate texture, and {11–20} <0001> plate texture, are also complicated than that of BM ({0001} <11–20> plate texture), and the texture intensity is also higher. Besides, the mechanical properties of the FZ are inferior, due to the microstructure and mechanical properties evolution. Specifically, the tensile strength of the BM, upper part and bottom part of FZ are 695 MPa, 644 MPa, and 679 MPa and the impact energy of the BM and FZ are calculated as 201.7 J/cm2 and 70.7 J/cm2, respectively. The hardness of the FZ (200–220 HV1) is lower than that of the BM (230-250 HV1). This study first comes to attention to systematically characterize and analyze the weldability, as well as the microstructure evolution and mechanical properties of the weld joint, of Ti–4Al–2V alloy, which will lay a solid foundation for the engineering application of this alloy in the future.

Machine learning classification-based approach for mechanical properties of friction stir welding of copper

The paper presents a machine learning classification-based model for a friction stir welded copper's mechanical properties. The models train and test 119 experimental data for the pure copper system to study the effect of process parameters on FSW copper joints' mechanical properties. Four classification models were employed to analyze the impact of process parameters on the mechanical properties. The deep learning-based neural network model exhibited the highest accuracy of 94%. The machine learning model suggested that tool features and design were the most important parameters influencing the joint's mechanical property.

Study on microstructure and properties of Mg/steel laser welding-brazing joint assisted by alternating magnetic field with Ni interlayer

The laser welding-brazing technology assisted by alternating magnetic field was adapted to Mg/steel dissimilar materials with Ni interlayer. Microstructure and mechanical properties of joints were compared with and without alternating magnetic field. The results showed that the weld width L was enlarged and ensured good weld formation and weld quality by applying the alternating magnetic field. The joint was comprised of Mg side weld zone, intermetallic compound (IMC) layer and steel side weld zone. The effect of mechanical occlusion was enhanced by the appearce of zonal structures of Fe–Ni solid solution in the Mg side weld zone and the serrated Mg2Ni in the brazing zone of IMC layer. A continuous nano scale AlNi layer formed in the fusion welding zone of IMC layer, which is conducive to strengthen the joint. The optimal joint assisted by appropriate alternating magnetic field was obtained with tensile and shear strength enhanced by nearly 15%.

Mechanical properties of radial spherical plain bearing (RSPB) joint with an inserted plate for building structural application – An experimental study

In the extension project of the China National Academy of Painting, the radial spherical plain bearing (RSPB) is used in a structural joint with an inserted plate. This new structural RSPB joint has complicated mechanical behaviors and universal rotational performance. In this work, the simulation and experiment methods were used to investigate the RSPB joint mechanical properties (uniaxial ultimate bearing capacity, failure mode) and reliability. Furthermore, the out-of-plane rotational performance was studied with eight finite models for the application. According to FEA and test results, this new RSPB joint has functional mechanical properties. It is useful in steel truss structures and provides a possibility for engineers to design hinge joints in building structures.

Effect of parametric study on microstructure during FSW process

The work focuses on the improvement of strength-weldability combination in Friction Stir Welding (FSW) joint of 7075 and 6061 Aluminium Alloys. Although Al-6061 and Al-7075 both are heat treatable but they are having somewhat different mechanical properties. The 7075-T6 has more tensile strength and hardness than that of 6061-T6.The lower hardness of 6061-T6 allow it to weld easily whereas 7075 prone to cracking during welding. Owing with the result that FSW could play significant role in order to improve the weldability, microstructure of cross section as well as the mechanical properties of joint was characterized. The welds were considered by using three rotational speed and three feed. It was revealed that the tensile strength of the joint (153.13 MPa) became very less in comparison to the base metal and it has been decreased again when the speed decreases from 700rpm and 15mm/sec to 2000rpm and 25mm/min.The findings such as tensile strength as well as the fracture revealed that mechanical properties and the microstructure of welding are not desirable for any structural application.

Finite element analysis of mechanics performance for GFRP beam-column joints connected by angle steel with slotted-hole

In this paper, a group of GFRP beam-column joints connected with slotted-hole angle steel were analysed under monotonic loading. Based on ABAQUS software, the nonlinear finite element analysis of slotted-hole on beam for GFRP joint and influence of different slotted-hole lengths on mechanical properties of joints were carried out. Considering influence of friction and pretightening force, a conventional circular hole specimen C1 and three specimens K2, K3 and K4 with slotted-hole lengths of 2mm, 4mm and 6mm were designed. The universal contact element and pretension element were applied on ABAQUS finite element modeling of bolted connections. Finally, differences in failure mode, moment-rotation curve, rotational capacity, displacement ductility coefficient and other aspects between angle steel joints with conventional round holes and those with different slotted-hole sizes were compared. The results show that: 1) the rotational capacity of slotted-hole joints was about 6%-19% higher than that of ordinary round-hole joints. The longer the slotted-hole length is, the larger the plastic rotation angle steel will be. However, too large slotted-hole size will also cause excessive deformation of components and collapse.2) The slotted-hole method will not increase bearing capacity of joints, but displacement ductility coefficient of joint K4 with slotted-hole size of 6mm was 1.17 times that of conventional joint C1 with circular hole.

Friction stir spot welding of dissimilar ABS and PA6 by a tool with newly designed tooth-shaped flat pin

Dissimilar Acrylonitrile Butadiene Styrene (ABS) and Polyamide 6 (PA6) are hard to be welded due to their poor compatibilities. In this paper, a flat-pin tool with long tooth-shaped tip was designed and utilized to friction stir spot weld ABS and PA6 plates. Annular PA6 anchor and column were produced, which enhanced the mechanical interlocking between the lapped sheets. Rotational speed (S R ) was found to be influential to the weld formation, PA6 morphology and joint mechanical property. PA6 column became short and PA6 anchor gradually disappeared with the increase of S R . The PA6 particles were large and poorly connected with ABS matrix under S R 250. A large amount of PA6 particles were refined to a few microns or even hundreds of nanometers under S R 350, presenting spherical and rod-shaped morphologies. Meanwhile, their connection with ABS matrix became compact. Under S R 500, pores emerged in the nugget and gaps were generated along the nugget boundary. Lap-shear tensile tests showed that the fracture loads of the joints decreased with increased S R and two failure modes were observed. Elongated PA6 bands, deep holes and dimples were observed on the fracture surface of the nugget obtained under S R 350.

Multi-properties optimization of welding parameters of wire arc additive manufacture in dissimilar joint of iron-based alloy and nickel-based superalloy using grey-based Taguchi method

In order to adapt to the high temperature and heavy load process environment of large forgings, a novel die with “fist-like” structure was designed. The iron-based welding material (RMD248) as the “bone” layer and the nickel-based superalloy welding material (ERNiCr-3) as the “skin” layer were welded on the matrix by wire arc additive manufacture (WAAM). In this work, the grey based Taguchi methodology was used to optimize welding parameters (welding voltage, welding speed and wire feed speed) considering excellent multi-properties (hardness and ultimate tensile strength of high-temperature tensile test) of the dissimilar joint of RMD248 and ERNiCr-3. Further, analysis of variance was done to ascertain the influence of welding parameters on response parameters. Experimental results showed that welding speed was the most effective input parameter followed by wire feed speed and welding voltage. Finally, optimal result was verified through confirmation experiments. Meanwhile, the effect of welding speed on the microstructure and mechanical properties of joint was studied. The microstructures were characterized by optical microscopy (OM), energy dispersive spectrometer (EDS). The results indicated that the microstructure of RMD248 was consisted of more retained austenite at lower welding speed. For ERNiCr-3, the finer columnar crystal structure at higher welding speed was observed. At lower welding speed, the microhardness of RMD248 was just slightly lower, but that of ERNiCr-3 was significantly higher, and the ultimate tensile strength was higher. Therefore, the specimen at lower welding speed had better comprehensive mechanical properties.

Atomic-scale simulation of nanojoining of Cu-Ag core-shell nanowires

Effective fabrication methods of Cu-Ag core-shell nanowires network are of vital importance for their shining applications in stretchable electronics. In this study, molecular dynamics simulations are performed to study nanojoining of Cu-Ag core-shell nanowires by head-to-head cold welding, along with mechanical properties of obtained welding joints. Results show that Cu-Ag core-shell nanowires can be successfully connected by cold welding with high-efficiency and few defects owing to atomic interaction and diffusion of atoms. What's more, welding velocity and remaining deformation in nanowires will exert significant influence on mechanical properties of joints, including strength and plasticity. It is revealed that cold welding under pressure will somewhat cause internal compression of structures which can be alleviated by following tensile deformation of the two heads if possible. These findings deepen the understanding of nanoscale cold welding and are expected to provide practical reference for the bottom-up fabrication and assembly of Cu-Ag core-shell nanowires network.

Study of the mechanical properties and microstructures of conical joints for aluminum/steel continuous drive friction welding

Presetting the taper on a joint will change the thermodynamic cycle of the interface in the direction of the rotating friction radius and affect the structure and joint mechanical properties. In this research, five types of conical Q235 low carbon steel rods at 5°, 10°, 15°, 20°, and 25° were paired with 1060 aluminum rods performed with continuous drive friction welding butt joint experiments. For these experiments, the temperatures of the interface center as well as 1/3R and 2/3R were collected during the welding process. After welding, the joints were subjected to tensile testing, fracture analysis, and microstructure analysis of the joint interface. The results showed that for the same process parameters, the increase in the tilt angle of the conical end face made the corona bonds of the friction interface of the joint move from the outside to the inside due to a decrease in the friction heat and an increase in the tangential stress, and the corona bonds became narrower. For certain technological conditions, a reasonable cone could improve the homogenization of the radial intermetallic compounds at the joint interface. The thickness of the intermetallic compound layer of the 15° tilt angle joints had the smallest gradient along the radius. The average thickness was about 0.85 μm and the average tensile strength reached a maximum of 77.5 MPa. This was 96 % of the base material of 1060 pure aluminum.

Study on the effects of transverse ultrasonic vibration on deformation mechanism and mechanical properties of riveted lap joints

In this paper, a new and special transverse ultrasonic vibration-assisted riveting (TUVR) system is developed to improve the plasticity and qualification of titanium alloy rivets. Comparing with conventional riveting (CR), the formed driven heads by TUVR are not only suffered from the riveting force and hole boundary constrain, but also the acoustic softening and dragging friction force. Consequently, to disclose the deformation mechanism and mechanical properties in driven head, a series of studies were carried out. First, the dimensions of driven head for different amplitudes and roughness were investigated. On this basis, the typical position microstructures in driven head of TUVR and CR were contrastively analyzed. Moreover, the interference sizes of laminates riveted lap joints under CR and TUVR were compared. Finally, the micro-hardness and pull-out strength in joints of two riveting processes were tested, and illustrating the mode and microstructure of failure. Results show that ultrasonic vibration can act as a new and effective auxiliary riveting method, which contributes to achieving plasticity improvement and higher mechanical properties of joints. Although the TUVR has significant effects on the deviation of the driven head, which can be restrained well with a reasonable amplitude and roughness. The grains deformation in typical positions of TUVR is much severer than CR, except in the lower shear band and difficult deformation area. Besides, the uniformity of interference sizes of riveted sample is well improved by TUVR. The experimental results show that the micro-hardness and yield load of TUVR riveted lap joints increase more than 10% and 4%, respectively.

Joining of ultra-high-strength steels using resistance element welding on conventional resistance spot welding guns

Single-step joining of dissimilar material combinations between ultra-high-strength steels and high-strength aluminium alloys with sufficient mechanical joint properties by using conventional resistance spot welding equipment has not been reported yet. In this research paper, a novel single-step joining technology, so-called self-penetrating resistance element welding, is introduced. First, the motivation for this novel joining technology, the state of the art in joining, and the process characteristics are presented. In the results section, the welding rivet geometry is first determined using forming simulations and validated by head tensile tests. Followed by the description of the welding process and its characteristics, the mechanical joint properties are reported. The results show that a numerically optimised welding rivet geometry can guarantee sufficient joint strength. By this welding rivet geometry, a thermally assisted penetration of aluminium and therefore welding to steel is possible with and without adhesive. Furthermore, it is shown that the welding process can be designed by means of simulations. Finally, the shear tensile tests prove that an overall sufficient joint strength is ensured.

Vacuum Brazing of C/C Composite and TiAl Intermetallic Alloy Using BNi-2 Brazing Filler Metal.

C/C composite was brazed to TiAl intermetallic compound using a commercial BNi-2 brazing filler metal under vacuum brazing condition. The brazing temperature was 1030~1150 °C and the holding time was 20 min. The joint interfacial microstructures and mechanical properties were studied, and the fracture behavior and joining mechanism were also investigated. The effect of brazing temperature on the joint shear strength was explored. The results showed that a perfect interface joint can be obtained by using BNi-2 to braze C/C and TiAl. During brazing, Ti, Cr, and other carbide forming elements diffused to C/C composite side, forming Cr3C2, Cr7C3, TiC, and other carbides, and realizing metallurgical joining between the brazing filler metal and C/C composite. The microstructure of the interface of C/C composite and TiAl intermetallic compound joint is as follows: TiAl alloy → TiAl + AlNi3 → AlNi2Ti → Ni(s, s) + Ti3Al + Ni3Si → Ni(s, s) + Ni3(Si, B) + CrB → Ni(s, s) + Ni3Si + TiCr2 → (Ti, Cr)C → C/C composite. When the holding time is fixed, with the increase of brazing temperature, the shear strength of the joint increases first and then decreases. The maximum average room temperature shear strength of the brazed joint was 11.62 MPa, while the brazing temperature was 1060 °C and the holding time was 20 min.

A Review of Sintering-Bonding Technology Using Ag Nanoparticles for Electronic Packaging.

Metal nanoparticles (NPs) have attracted growing attention in recent years for electronic packaging applications. Ag NPs have emerged as a promising low-temperature bonding material owing to their unique characteristics. In this study, we mainly review our research progress on the interconnection of using polyol-based Ag NPs for electronic packaging. The synthesis, sintering-bonding process, bonding mechanism, and high-temperature joint properties of Ag NP pastes are investigated. The paste containing a high concentration of Ag NPs was prepared based on the polyol method and concentration. A nanoscale layer of organic components coated on the NPs prevents the coalescence of Ag NPs. The effects of organic components on the bondability of the Ag NP paste were studied. Compared to the aqueous-based Ag NP paste, the polyol-based Ag NP with the reduction of organic component can improve the bondability, and the coffee ring effect was successfully depressed due to the increased Marangoni flow. The sintering behaviors of Ag NPs during the bonding process were investigated using the classical sphere-to-sphere approach. The mechanical property of joints using this Ag paste was better than that using Pb95Sn5 solders after storage at high temperatures. The sintering–bonding technology using polyol-based Ag NPs was helpful to the low-temperature interconnection for electronic packaging applications.

Effects of the beam offset on microstructure and properties of electron beam welded tantalum and Inconel 718 joints

In this paper, electron beam welding of tantalum and Inconel 718 superalloy was performed. The formability, microstructure, defect characteristics and mechanical properties of joints were investigated by controlling the position of the electron beam. The weld zone of tantalum and Inconel 718 joints was mainly composed of columnar crystals and dendrites during the welding of non-beam offset and 0.5 mm beam offset to tantalum. The reaction layer composed of a large number of intermetallic compounds was found on the tantalum side, and it was the place where the fracture occurred. Tensile strength of the joints was 313 MPa and 138 MPa, respectively, and the joints exhibited brittle fracture mode due to the formation of voids and cracks in the reaction layer. The microhardness of the weld zone was higher than that of the base metal due to the strengthening effect of tantalum. Fortunately, when the beam deviated by 0.5 mm to the Inconel 718 side, equiaxed grains formed in the weld zone, and the morphology of the reaction layer changed, which improved the toughness of the joint. The tensile strength of the joint reached 480 MPa under the condition of 0.5 mm beam deviated to the Inconel 718 side.

Impact of travel speed on the microstructure and mechanical properties of adjustable-gap bobbin-tool friction stir welded Al-Mg joints

The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study. The microstructure was studied using optical microscopy and electron backscatter diffraction (EBSD). Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechanical properties. Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed increased. The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in different regions of the joint vary depending on the recovery and recrystallization behavior. Specific attention was given to the relationship between the local microstructure and mechanical properties. Microhardness measurements show that the average hardness of the stir zone (SZ) was greater than that of the base material, which was only affected slightly by the travel speed. The tensile strength of the joint decreased with increasing travel speed and the maximal strength efficiency reached 99%.

Joining silicon nitride ceramics in air by pure aluminum filler

Reliable Si3N4/Si3N4 joints is successfully prepared in air using pure Al filler. The interfacial microstructure, phase composition and mechanical properties of the joint are investigated in detail. The effects of joining temperature on joint structure and mechanical properties are studied. The experimental results indicate that the diffusion occurs at the interface between Si3N4 ceramics and Al filler. A maximum shear strength of ~42 MPa is obtained for joints joining at 950 °C for 1 h. The work makes an attempt on the joining of Si3N4 ceramics in air, which broadens the joining method of Si3N4 ceramics.

Influence of post welding heat treatment on the microstructure and mechanical properties of friction stir welding joint of AZ31 Mg alloy

At present, magnesium alloys are extensively used in numerous applications due to their light weight and better characteristics. Welding of magnesium alloys is regarded as one of the most complex phenomena in various industries. The friction stir welding of magnesium alloys has encouraged abundant scientific and industrial interest as it has the potency to form a good quality joint. Post welding heat treatment is an appropriate process to further improve the properties or performance of FSW joints. Therefore, the present work aims to join AZ31 Mg alloy plates by friction stir welding, and microstructural and mechanical properties of the joint have been examined. Furthermore, the consequence of post welding heat treatment on the microstructure and mechanical properties of FSW joint has been evaluated. Tensile strength and elongation of FSW joint were about 145.4 ± 4.9 MPa and 9.5 ± 0.9%, respectively. It was found that post welding heat treatment was beneficial in homogenizing grains and to enhance mechanical properties. Tensile strength and elongation of the joint were improved by 4.74% and 15.78% respectively after PWHT. The highest microhardness of stir zone decreased about 6.84% (73 Hv to 68 Hv) after heat treatment and hardness pattern of weld became relatively smooth. Toughness of PWHT joint was 4.5 ± 0.17 Joules. The mode of tensile failure of as-welded and PWHT joint was ductile.