Mechanical Properties Of Dissimilar Joints Research Articles

Microstructure and Mechanical Properties of Mg-Li/Al Dissimilar Joints via Dynamic Support Friction Stir Lap Welding.

In this study, two-mm-thick dual-phase LA103Z Mg-Li and 6061 Al alloys, known for their application in lightweight structural designs, were joined using dynamic support friction stir lap welding (DSFSLW). The microstructural evolution and mechanical properties of dissimilar joints were investigated at different welding speeds. The analysis revealed two distinct interfaces: the diffusion interface and the mixed interface. The diffusion interface, characterized by a pronounced diffusion zone, is formed under slower welding speeds. The diffusion zone height, the effective lap width, and the interface layer thickness decrease with increasing welding speed due to low plastic deformation capacity and weak interfacial reactions. Conversely, the mixed interface, associated with higher welding speeds, contained large Al fragments. The extremely high microhardness values (130.5 HV) can be ascribed to the formation of intermetallic compounds (IMCs) and strain-hardened Al fragments. Notably, the maximum shear strength achieved was 175 N/mm at a welding speed of 20 mm/min. The fracture behavior varied significantly with the interface type; the diffusion interface showed enhanced mechanical strength due to better intermetallic reactions and interlocking structures, while the mixed interface displayed more linear crack propagation due to weaker IMCs and the absence of hook structures. Fracture surface analysis indicates that fractures are more likely to propagate through the Al matrix and interface layers.

The effect of diffusion welding parameters on the microstructural characteristics and mechanical properties of dissimilar joint between AISI 418 stainless steel and Inconel 738 superalloy using nickel interlayer

The effect of diffusion welding parameters on the microstructural characteristics and mechanical properties of dissimilar joint between AISI 418 stainless steel and Inconel 738 superalloy using nickel interlayer

Effect of Welding Time Variation in Resistance Spot Welding on Mechanical Properties of Dissimilar Joints on Mild Steel and AISI 304 Stainless Steel

Resistance spot welding plays an important role in the automotive industry for working on car bodies or frames. Welding with two different steel materials is used in automotive structures. However, the low strength of the joints of different steel materials is a major problem, limiting the scope of its application. The quality of the welding connection Resistance spot welding is influenced by several factors, namely, time, welding current, and electrode pressure applied during welding and post-welding treatment. In this research, mild steel plate with AISI 304 stainless steel is welded by Resistance spot welding with different variations of welding time, material hardness and tensile testing that will be investigated. The results showed that the highest Rockwell Hardness time was obtained at a welding time variation of 8 seconds with a current of 6000 Ampere was 112.2 so the higher the welding time, the higher the hardness obtained. welding 8 seconds with a welding current of 6000 Ampere obtained a maximum tensile strength of 20.4 kgf/mm2 so the greater the welding current, the tensile strength will increase.

Nd: YAG laser beam welding of UNS N07718 superalloy and UNS S32304 duplex stainless steel: Phase transformations and mechanical properties of dissimilar joints

This article implies the phase transformations and mechanical behavior of dissimilar laser welded UNS N07718 superalloy/UNS S32304 duplex stainless steel. Laser power, welding speed, and focal point were the variables of the laser beam welding (LBW) approach. Optical microscopy and electron backscattered diffraction (EBSD) analysis were utilized. They demonstrated that the weld metal (WM) mainly had an austenitic microstructure with a face-centered cubic structure in the form of columnar and equiaxed dendrites. Also, the occurrence of directional solidification in WM was verified by EBSD. The heat-affected zone (HAZ) microstructure of Inconel 718 superalloy included austenite grains with normal grain growth, annealing twins, and precipitates. There was a ferritic-austenitic microstructure in the HAZ of 2304 duplex stainless. In this area, the volume fraction of the ferrite phase was excessively higher than that of the austenite phase and the austenite was characterized as Widmanstätten plates and grain boundary austenite. Furthermore, abnormal ferrite grain growth was identified in this. Welding defects e.g., molten spatter, solidification crack, and lack of penetration were observed, as well. Based on the uniaxial tensile test, it was realized that the highest failure load (9.7 ± 0.4 kN) was achieved in the laser power of 1900 W, welding speed of 3 mm/s, and focal point of 0 mm. Therefore, these variables were known as the optimum variables of the LBW process. All laser weldments failed from the WM and fractography via scanning electron microscopy (SEM) showed a mixture of dimple and cleavage features in the fracture surfaces of the laser welds.

Investigations of the mechanical properties of dissimilar joint of GTD-111 superalloy and 316 stainless steel obtained by laser welding

The objective of this study is to improve the mechanical properties of dissimilar joint between 316 stainless steel and GTD-111 superalloy obtained by laser welding. Hence, the input variables of pulse frequency, welding speed and laser power were employed to optimize the output variables of weld penetration, hardness and tensile strength through the desirability function technique and response surface methodology. In order to study the changes of microstructure in the welded samples, the optical and scanning electron microscopies were applied. It was observed that an increase in the laser power from 1500 to 2500 W enhanced the penetration depth of weld, while it worsened the hardness and tensile strength owing to nucleation of solidification cracks and formation of Laves phase caused by segregation of Ta, Ti, Nb, W, and Mo elements. Moreover, the faster welding speed up to 1.5 mm/s resulted in a decrease in the penetration depth and an increase in the hardness and tensile strength, which is due to the nucleation of a small dendritic structure and the nucleation of fewer Laves phase owing to lesser heat input. When the variables of pulse frequency and laser power increased simultaneously, the liquation cracks were formed within HAZ of GTD-111 superalloy due to nucleation of γ′-γ eutectic phase, while the cracks and shrinkage voids were observed within HAZ of 316 stainless steel. The results of desirability function technique indicated that the optimum mechanical properties have been obtained at a pulse frequency of 15 Hz, welding speed of 0.8 mm/s and a laser power of 1550 W.

Investigation of the Microstructure and Mechanical Properties in Friction Stir Welded Dissimilar Aluminium Alloy Joints via Sampling Direction

This research study investigates the influence of sampling direction on the microstructure and mechanical properties of dissimilar joints formed by friction stir welding (FSW). The specimens were cut in two directions: perpendicular (transverse) and parallel (longitudinal) to the FSW joint. The tests conducted included X-ray diffraction (XRD), macrostructure, microstructure, tensile, microhardness, and fractography analysis. Different phases were noted in the XRD patterns and explained, with the aluminum phase being the dominating one. The results further showed that the transverse dissimilar joint exhibited higher microhardness compared to the longitudinal dissimilar joint, which is consistent with the respective grain sizes. Moreover, the ultimate tensile strength of the longitudinal joint exceeded that of the transverse joints, showing a substantial 47% increase. Similarly, the elongation of the joints followed a similar trend, with the longitudinal joint displaying a significant 41% increase in elongation compared to the transverse joint. Fractographic analysis revealed ductile fracture behaviour in all joints.

Microstructure and Mechanical Properties of Dissimilar Friction-Welded Commercially Pure Ti and Ti–6Al–4V Alloy

Here, we investigated the microstructure and mechanical properties of dissimilar joints between grade 2 commercially pure titanium (CP-Ti-2) and Ti–6Al–4V alloy welded via friction welding. Accordingly, specimens with 15 mm diameter and 50 mm length were prepared, and friction welding was performed at a constant rotation speed (1600 rpm) and different upset lengths: 1, 2, and 3 mm. Electron backscattered diffraction (EBSD) method was introduced to systematically analyze grain boundary characteristic distributions (GBCDs), such as grain size, grain orientation, phase distribution, and misorientation angle distribution. In addition, mechanical properties of dissimilar joints were evaluated using the micro-Vickers hardness and tensile test machine. The microstructures at both sides of the CP-Ti-2 and Ti–6Al–4V alloy were refined materials, compared with each base material. These grain refinements were determined via dynamic recrystallization accompanied by frictional heat and severe plastic deformation. In addition, the increase in the upset length distinctively affected the change trend of the grain size of the CP-Ti-2 and Ti–6Al–4V alloy. The hardness values in regions around the weld interface were higher than those of base materials. Furthermore, yield and tensile strengths were maintained at a similar level to those of CP-Ti-2, and the tensile specimens were fractured at the base material zone of CP-Ti-2, not at the weld interface and its periphery. Consequently, friction welding to dissimilar joints between the CP-Ti-2 and Ti–6Al–4V alloy was successfully conducted and sound welded materials without welding defects were obtained.

Microstructure and mechanical properties of aluminum-steel dissimilar metal welded using arc and friction stir hybrid welding

In this study, arc and friction stir hybrid welding (AFSHW) was proposed to weld aluminum-steel dissimilar metals in attempt to realize high quality joining. Firstly, an interlayer was produced on galvanized steel by using bypass current-metal inert gas welding (BC-MIG), and then an aluminium plate was jointed via Friction stir lap welding (FSLW). The effects of tool pin length and FSLW times on the microstructure and mechanical properties of dissimilar joints were fully investigated by means of Optical Microscopy (OM), Scanning Electron Microscope (SEM), Electron Backscatter Diffraction (EBSD), and mechanical testing. The results show that as pin length increased, joint strength tended to increase and then decrease, and the tensile failure partially occurred at aluminium base metal. However, with additional number of FSLW, joint strength would be reduced, which was attributed to attenuated dislocation density and strain concertation in dissimilar joint. The research outcomes will provide a new welding method to obtain sound Al-Fe dissimilar metal joint, and benefit to a better understanding of Al-Fe joining mechanism.

Process optimization and thermodynamic modeling of weld zone in nickel powder-added dissimilar pulsed-laser NiTi/ASS joint

Dissimilar joining of NiTi alloys to stainless steel has attracted abundant consideration. In this research, pure nickel powder diluted in PVA adhesive was added to the joint area with different concentrations to eliminate or minimize the brittle intermetallic compounds. Also, thermodynamic concepts of phase stability employing the quaternary CALPHAD method were used to calculate the weld zone's phase stability. The results indicated that laser welding combined with 30% nickel powder addition did not have a noteworthy effect on detracting the content of Fe2Ti in the weld zone. In contrast, adding nickel powder with a concentration of 50% reformed the chemical composition and changed the Fe2Ti primary solidifying phase to more ductile phases of Ni3Ti and γ. The results of equilibrium thermodynamic calculations also predicted that Ni3Ti, γ, and B2-(Fe,Ni)Ti phases are possible to form in this condition. In laser welding with 70% nickel powder, unmixed nickel areas and gas porosities were observed in the weld zone. The superlative mechanical properties were obtained for the samples with 50% nickel powder addition. The microhardness results revealed a diminution of the weld zone's average hardness from 667 HV (without nickel powder addition) to 325 HV (50% nickel powder addition). Evaluation of joint strength revealed the twofold increase in 50% nickel powder added joints compared with conventional samples; the fracture strength and fracture strain reached 310 MPa and 2.9%, respectively. Therefore, Ni powder addition is an effective process for improving the mechanical properties of dissimilar joints of these two alloys.

Effect of welding mode and filler metal on microstructure and mechanical properties of dissimilar joints of S900MC thermomechanical steel to St52 carbon steel welded by gas tungsten arc welding

In this research, S900MC thermomechanical steel was jointed to St52 carbon steel through a gas tungsten arc welding process in the continuous and pulsed modes. The welding was performed in two different weld designs of V-groove and close square, with and without using an ER70S filler metal, respectively. Furthermore, the microstructure, hardness, and tensile strength of the joints were investigated. A bainitic microstructure was observed in the weld metal of the samples jointed in the continuous mode. While the weld metal microstructure of the pulsed joints was changed from a ferritic microstructure to a tempered martensitic microstructure by implementing filler metal in the V-groove weld design. In all joints, the heat-affected zone was narrower at the S900M side and had a fine bainitic microstructure. Among all joints, the maximum hardness of 389 HV was achieved for the weld metal of V-groove joints welded in the pulsed mode. At a normal strain rate, there was no considerable contrast between the yield and tensile strength of all joints, however, the elongation of the continuous joints was better than that of the pulsed joints. Increasing the strain rate led to the drastic improvement of yield and tensile strength of the joint welded in the continuous mode without using filler metal.

Study of the structure and mechanical properties of electron-beam-welded dissimilar joints of copper and stainless steel with and without offset

We present the results of an investigation of the structure and mechanical properties of dissimilar joints of copper and 304L stainless steel formed by electron-beam welding. The samples studied were welded without a beam offset and with a beam offset towards either welded materials to a distance of 0.3 mm. The phase composition was determined via X-ray analysis. The structure was investigated using scanning electron microscopy. The mechanical properties, including hardness and tensile strength, were measured. The phase composition of the considered specimens consisted of a double-phase structure of face-centered cubic (fcc) and body-centered cubic (bcc) phases. The sample welded without offset exhibited the highest yield strength and tensile strength values. The microhardness of all samples increased in the fusion zone on the steel side and decreased in the fusion zone on the copper side compared to the initial hardness of the two materials.

Mechanical Property Improvement in Dissimilar Friction Stir Welded Al5083/Al6061 Joints: Effects of Post-Weld Heat Treatment and Abnormal Grain Growth.

The 5083 and 6061(T6) aluminum (Al) alloys are widely used in transportation industries and the development of structural designs because of their high toughness and high corrosion resistance. Friction stir welding (FSW) was performed to produce the dissimilar welded joint of Al5083-Al 6061(T6) under different welding parameters. However, softening behavior occurred in the friction stir welded (FSWed) samples because of grain coarsening or the dissolution of precipitation-hardening phases in the welding zone. Consequently, this research intended to investigate the effect of the post-weld heat treatment (PWHT) method on the mechanical property improvement of the dissimilar FSWed Al5083-Al6061(T6) and governing abnormal grain growth (AGG) through different welding parameters. The results showed PWHT enhanced the mechanical properties of dissimilar joints of Al5083-Al6061(T6). AGG was obtained in the microstructure of PWHTed joints, but appropriate PWHT could recover the dissolved precipitation-hardening particle in the heat-affected zone of the as-welded joint. Further, the tensile strength of the dissimilar joint increased from 181 MPa in the as-welded joint to 270 MPa in the PWHTed joint, showing 93% welding efficacy.

Fracture dominant in friction stir spot welded joint between 6061 aluminum alloy and galvannealed steel based on microscale tensile testing

The macroscale mechanical properties of dissimilar joints are generally influenced by the fracture behavior of joint interface. However, little is known about the dominant factor for the joint properties related with both macroscale fracture behavior and microscale interfacial properties. Herein, microscale tensile testing of the joint interface was coupled with the macroscale fracture evaluation to elucidate the dominant factor of strength in dissimilar joints between 6061 aluminum alloy and high tensile strength galvannealed steel via friction stir spot welding (FSSW). Microstructural analyses revealed the characteristic formation of interfacial microstructure accompanied by friction and Zn discharge during the FSSW process. Microscale tensile testing was performed on the specimen on which the pre-notch was introduced to induce local fracture at the intended position on the joint interface. Results showed the presence of the weakest interface attributed to initial joining defects formed by Zn concentration at the outer area, which were consistent with the outside of the crack arresting area confirmed by macroscale evaluation. These results indicated that the joint strength of dissimilar joints between 6061 aluminum alloy and galvannealed steel is dominated by the local strength of the joining area without defects and suggested a process design for improving dissimilar joints.

Phase identification and thermodynamic modeling of a quaternary system in dissimilar laser-welded NiTi/ASS

Defect-free joints of NiTi/austenitic stainless steel wires have extraordinary combined properties of shape memory, superelasticity, and biocompatibility. However, problems arise from the dissimilar welding of NiTi to stainless steel, including the formation of brittle intermetallic compounds and the loss of shape memory and superelastic properties. To overcome the welding challenges of these alloys, phases formed in the weld zone must be identified. Therefore, we used CALPHAD quaternary phase analysis to predict the formation of intermetallic compounds and other probable phases in the weld zone. The calculated results were compared with existing ternary phase diagrams containing Fe, Ni, Ti, and Cr. According to these calculations and experimental observations using electron backscatter diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and micro X-ray diffraction techniques, brittle Fe2Ti is the predominant phase in the final solidified structure, even in the equilibrium state at the NiTi-weld interface. In addition, a ductile Ni3Ti phase, together with the γ-(Fe,Ni) and B2-(Fe,Ni)Ti phases, is feasible in the weld zone. Moreover, Cr appears as a solid solution with Fe and Ti (BCC_A2 and β(Cr,Ti)) at low Cr concentrations. At higher concentrations, Cr can potentially appear as a σ phase and a C14 Laves phase, which can cause a stress concentration at the NiTi-weld interface, degrading the mechanical properties of dissimilar joints. Therefore, a suitable modification process is required to improve the mechanical properties of NiTi to stainless steel joints. Thus, any adopted strategy should preclude brittle Fe2Ti and facilitate the formation of more ductile phases such as γ-(Fe,Ni).

Enhanced Long-Term Reliability of Seal DeltaSpot Welded Dissimilar Joint between 6061 Aluminum Alloy and Galvannealed Steel via Excimer Laser Irradiation.

Structural-adhesive-assisted DeltaSpot welding was used to improve the weldability and mechanical properties of dissimilar joints between 6061 aluminum alloy and galvannealed HSLA steel. Evaluation of the spot-weld-bonded surfaces from lap shear tests after long-term exposure to chloride and a humid atmosphere (5% NaCl, 35 °C) indicated that the long-term mechanical reliability of the dissimilar weld in a corrosive environment depends strongly on the adhesive–Al6061 alloy bond strength. Corrosive electrolyte infiltrated the epoxy-based adhesive/Al alloy interface, disrupting the chemical interactions and decreasing the adhesion via anodic undercutting of the Al alloy. Due to localized electrochemical galvanic reactions, the surrounding nugget matrix suffered accelerated anodic dissolution, resulting in an Al6061-T6 alloy plate with degraded adhesive strength and mechanical properties. KrF excimer laser irradiation of the Al alloy before adhesive bonding removed the weakly bonded native oxidic overlayers and altered the substrate topography. This afforded a low electrolyte permeability and prevented adhesive delamination, thereby enhancing the long-term stability of the chemical interactions between the adhesive and Al alloy substrate. The results demonstrate the application of excimer laser irradiation as a simple and environmentally friendly processing technology for robust adhesion and reliable bonding between 6061 aluminum alloy and galvannealed steel.

Investigation of mechanical properties of dissimilar joint of Al6063 aluminium alloy and C26000 copper alloy by ultrasonic assisted friction stir welding

An attempt by this experiment has been made to analyse the difference of mechanical properties in welding among Friction Stir Welding (FSW) and Ultrasonic assisted Friction Stir Welding (UAFSW). Dissimilar metals 6063 Aluminium Alloy with C26000 Copper alloy are joined in this experiment. Optimum mechanical properties obtained by FSW and UAFSW by calibrating tool rpm range from 400 to 600 rpm with tool transverse rate from 15 to 25 mm/min were obtained and compared. For UAFSW calibration of tool rpm ranges from 400 to 600 rpm tool transverse rate from 15 to 25 mm/min assisted by ultrasonic frequency ranging from 10 to 14 kHz were used. An improvement in the mechanical property observed by addition of the ultrasonic energy to FSW process and been presented in the paper and the ultrasonic vibration used in the study has been observed to be suitable in the range of 10–14 khz for joining dissimilar material under study. Also, an improvement of mechanical properties from 10 to 25 % been observed by addition of the ultrasonic energy to FSW process. The comparative results of the UTS, YS and elongation were explained and presented for FSW and UAFSW process showing the improvement in the material property due to the addition of Ultrosonic energy.

Effect of Bonding Temperature on Microstructure and Mechanical Properties of Dissimilar Joint Between Inconel 617 and Stainless Steel 310

Effect of Bonding Temperature on Microstructure and Mechanical Properties of Dissimilar Joint Between Inconel 617 and Stainless Steel 310

Strength improvement in friction stir spot joining of polyethylene and aluminum

Abstract The effect of surface condition, dwell time and plunge rate on the mechanical properties of dissimilar joints between polyethylene and aluminum were investigated. The scratches made by the mandrels on the aluminum surface acted as mechanical locks and hence the strength of the dissimilar joint was increased. An increased dwell time and a decreased plunge rate exhibited a positive effect on the bond strength values. The major joining mechanisms were mechanical interlocking between the sheets and wetting of the aluminum surface by the molten polyethylene. The increase in the actual contact area due to the increased surface roughness, improved the shear-tensile load of the joint (up to 56%).

An assessment of microstructure and mechanical properties of inconel 601/ 304 stainless steel dissimilar weld

The microstructure and the mechanical properties of dissimilar joints between Inconel 601 superalloy and 304 austenitic stainless steel were investigated in this work. For this purpose, gas tungsten arc welding (GTAW) process was performed using an austenitic (ER304) stainless steel filler metal in two modes of pulsed and constant current conditions in pure (99.999%) argon gas. Furthermore, an autogenous welding (without filler metal) procedure was also carried out for comparison. The microstructure of weldments was investigated using optical and scanning electron microscopy. Tensile tests and microhardness measurements were carried out to evaluate the mechanical properties. High vacuum FE-SEM investigations revealed that no segregation has occurred in the weld metal. It was found that a decrease in heat input led to a significant grain refinement in the welds, which improved the mechanical properties. Among the welds fabricated with filler metals, welding with pulsed current resulted in superior mechanical properties. Finally, an excellent strength ductility matching (UTS = 485 MPa and Elongation = 39%) was obtained by autogenous welding procedure.

Investigation of mechanical properties of dissimilar joint of 6063 aluminium and C26000 copper alloy by friction stir welding

In this study, Aluminium 6063 and copper alloy C26000 has been selected, on the basis of industrial utilisation in marine industry like shipbuilding, oil piping system and marine super-structure, for joining by Friction Stir Welding and the mechanical properties has been studied upon. Three process parameters have been chosen in the present studies, like tool tilting angle, rpm and weld speed. Taguchi L9 array has been chosen for the experimental methodology and the by varying the selected process parameters, the mechanical properties including the weld efficiency and hardness, in advancing and retreating side, have been studied and compared. The mechanical properties obtained including elongation, yield strength, tensile strength and hardness in the various heat affected zones has been studied to define the utilisation of the FSW process in marine industry.