Showing papers on "Butt joint published in 2022"

Weld pool dynamics and joining mechanism in pulse wave laser beam welding of Ti-6Al-4V titanium alloy sheets assembled in butt joint with an air gap

Abstract: A validated CFD model coupling the multiple phases and multiple physics was developed for the dynamic simulation of pulse wave laser welding (PWLBW) process of 1.2 mm-thick Ti-6Al-4V alloy sheets assembled in butt joint with a reserved air gap. A laser spot diameter of 700 μm was used to compensate for the energy loss with the clearance applied at 0.2 mm and therefore improve the gap bridging ability. The distributions and evolutions of temperature, velocity, phase interface and weld pool dimensions were characterized and discussed to reveal the joining mechanism and the heat and flow behaviors during welding. The results show that the liquid bridges firstly occur in the middle height of sheets as the welding begins, and rapidly extend to the whole thickness with the increasing heat input. The reduction on laser power causes the rebounding of keyhole surface and the backfilling of molten metal. The keyhole closes at root surface and rebounds completely in 2 microseconds, leading to the merging of liquid bridges, bottom-up moving of high temperature area, and temporarily enlargement on weld pool size at root surface. During the pulse interval, the weld pool volume shrinks significantly and the molten metal slows down from Marangoni vortexes to thermal buoyance flows. The proposed process parameters allow an air gap accounting for 16.67% of specimen thickness and result in a well-formed and defect-free weld bead.

Application of an Artificial Neural Network in the Modelling of Heat Curing Effects on the Strength of Adhesive Joints at Elevated Temperature with Imprecise Adhesive Mix Ratios

Abstract: This paper is a discussion of the results of tests intended to (i) estimate the effects of component mix ratios and heat curing of an adhesive joint on the tensile strength, and (ii) to determine the adhesive component mix ratio for which heat curing is insignificant to the strength of adhesive butt joints. Experimental tests were carried out at ambient temperature and elevated temperature during which adhesive butt joints were loaded with a tensile force until failure. The variables were the mix ratio of epoxy adhesive components and the application of heat holding at the adhesive curing stage. An LSTM (long short-time memory) forecast was used to determine the point corresponding to the mix ratio of adhesive components at which heat holding of the adhesive joint no longer has a positive and significant importance to the final tensile strength of the joint.

Improving intermetallic compounds inhomogeneity of Ti/Al butt joints by dual laser-beam bilateral synchronous welding-brazing

Abstract: To regulate the inhomogeneous interfacial reaction during laser welding-brazing of Ti/Al dissimilar alloys, an advanced method of dual laser-beam bilateral synchronous welding-brazing was proposed. The formation mechanism of the intermetallic compounds (IMCs) with various dual laser-beam input was analyzed. The experimental results revealed that sound brazing joints with homogeneous serrated-shaped IMCs along the Ti/Al interface were obtained when the laser power on both sides is the same. An interesting phenomenon can be found that the thickness of IMCs layer on both sides is thicker than the middle. The highest bonding strength of Ti/Al butt joints could reach up to 71% of aluminum alloy base metal due to homogeneous serrated-shaped IMCs with a thickness of 3–4 μm.

Influence of contact behavior on welding distortion and residual stress in a thin-plate butt-welded joint performed by partial-length welding

Abstract: Partial-length butt-welded joint is a typical weldment which is often used in vehicle parts such as car door and body. In order to clarify the influence of contact behavior on the final distortion and residual stress distribution in thin-plate butt-welded joints, a computational approach considering multiple nonlinearities was proposed based on ABAQUS code, and a series of three-dimensional thermal–elastic–plastic finite element models were developed to simulate welding distortion and residual stress in mild steel thin-plate butt-welded joints performed by partial-length welding. Meanwhile, the corresponding experiments were carried out to verify the calculation accuracy of the proposed computational approach. Moreover, the influence of initial gap size on welding distortion and residual stress was numerically and experimentally examined. Based on the simulated results, the formation mechanism of welding deformation in the thin-plate partial-length butt-welded joint was also discussed.

Selected Properties of RAMOR 500 Steel Welded Joints by Hybrid PTA-MAG

Abstract: The paper describes the selected properties of RAMOR 500 anti-ballistic (martensitic structure in the initial state) high yield strength steel (1450 MPa) welded joints produced by the hybrid PTA-MAG (Plasma Transferred Arc - Metal Active Gas) method. The welded elements were metal sheets 6.7 mm thick in a rectangular shape with dimensions of 200 mm x 350 mm. The tested butt weld joints have been made with process parameters selected according to criterion of lowest level of material weakening in the heat-affected zone (HAZ). The results of metallographic research of welds heat affected zone and base material, hardness distribution and XRD patterns of specific areas have been presented. Depth-sensing indentation (DSI) is used in this work to determine the distribution of mechanical properties affected by annealing/tempering by thermal cycle of hybrid PTA-MAG welding process. The investigation results show that the use of hybrid PTA-MAG heat source for welding of martensitic structure steel makes it possible to use high strength steel filler material (yield strength 890 MPa) without of cold cracks high risk. The hybrid plasma based welding method has a potential to become a beneficial alternative to other welding processes for ballistic protection steel due to its high efficiency, reduced amount of weld metal content or limited requirements for a preparation of edges of welded joints. The weakest area of welded joints is part of HAZ located close to the base material which has been secondarily tempered by heat of welding thermal cycle. The heat input about 0,57 kJ/mm required to achieve full penetration butt welded joints with no defects and with wide enough capillary channel to cover the welding gap during welding process. Hardness decrease in that area is about 25% in relation of base material. The width of the softened zone was approx. 4.5 mm.

Improving intermetallic compounds inhomogeneity of Ti/Al butt joints by dual laser-beam bilateral synchronous welding-brazing

Abstract: To regulate the inhomogeneous interfacial reaction during laser welding-brazing of Ti/Al dissimilar alloys, an advanced method of dual laser-beam bilateral synchronous welding-brazing was proposed. The formation mechanism of the intermetallic compounds (IMCs) with various dual laser-beam input was analyzed. The experimental results revealed that sound brazing joints with homogeneous serrated-shaped IMCs along the Ti/Al interface were obtained when the laser power on both sides is the same. An interesting phenomenon can be found that the thickness of IMCs layer on both sides is thicker than the middle. The highest bonding strength of Ti/Al butt joints could reach up to 71% of aluminum alloy base metal due to homogeneous serrated-shaped IMCs with a thickness of 3–4 μm.

Friction stir butt-welding of roll cladded aluminum thin sheets: effect of microstructural and texture changes on mechanical properties

Abstract: Experimental studies are carried out on the friction stir butt-welded aluminum (Al)-clad-aluminum thin sheets. Aluminum alloy 4343 (AA4343, Al–Si series) and 3003 (AA3003, Al–Mn series) act as the clad layer and the core of the Al-clad-Al material system, respectively. Optical microscopy confirms that the joining is achieved successfully without macroscopic defects, while the clad layer is mixed into the core, mostly in the advancing side (AS) of the stir zone (SZ). Outside the SZ, no delamination between the clad layer and core is observed. Material flow analysis with electron probe microanalyzer exhibits the flow of silicon (Si) particles from the clad layer to the core resulting in several Si-induced precipitations of α-Al(Fe, Mn)Si, α-AlMnSi inside the SZ. The heterogeneous distribution of those precipitates is visualized by scanning electron microscopy and their compositions are analyzed using an energy dispersive X-ray spectrometer. Electron back-scattered diffraction maps reveal dynamically recrystallized ultra-fine grain structures (3.7–3.9 μm) inside the SZ. The mechanical properties of the joint are evaluated by cross-sectional 2D microhardness mapping and uniaxial tensile tests. Inside the SZ, the grain refinement with the formation of Si precipitation increases the tensile strength and microhardness of the joint.

Friction stir welding for manufacturing of a light weight combat aircraft structure

Abstract: Abstract This paper aims to validate the viability of friction stir welding process (FSW) to join high strength aerospace grade AA2014-T6 aluminium alloy for manufacturing light-weight combat aircraft (LCA) structure as a replacement to riveting process. FSW is used to overcome the heat input-related problems in fusion welding of AA2014-T6 aluminium alloy such as coarse grain fusion zone microstructure, softening in HAZ and lower joint efficiency. The 2 mm thick AA2014-T6 aluminium alloy sheets were used as the base material (BM). Friction stir butt (FBW) and friction stir lap (FLP) joints were developed, and its performance was compared with double cover riveted butt (DRB) joint in butt (RBJ) and lap (RLJ) joint configuration. Results showed that the load-carrying capability of FSW joints is greater than the riveted joints. The superior load-carrying capacities of FBW and FLW joints refers to evolution of refined grains and strengthening precipitates in stirred zone (SZ), which ensures superior metallurgical bonding between the joining surfaces. The riveted joints disclosed inferior load-carrying capacities due to the lack of metallurgical connection between the joining surfaces.

Mechanical performance and formability of laser-welded dissimilar butt joints between medium-Mn stainless steel and high-strength carbon steel

Abstract: The mechanical performance and stretch formability of dissimilar butt joints between medium-Mn stainless steel (MMn-SS) and high-strength carbon steel (HS-CS) processed by laser welding using different parameters were studied under uniaxial and biaxial loadings applied by tensile and Erichsen cupping tests, respectively. Laser scanning microscopy and electron backscatter diffraction (EBSD) were used to study the microstructural evolution. An electron probe microanalyzer (EPMA) was employed to analyse the distribution of alloying elements within the weld zone. The dominating deformation mechanisms operating in the paired metals during stretch-forming were identified through EBSD analysis. The study revealed that a fully martensitic microstructure is promoted in the fusion zones (FZs) of the weldments processed with low and high specific point energy (SPE 19, 25, and 30 J). Consequently, hardness values of the FZs were slightly decreased with SPE. Similarly, tensile properties were not affected since failure occurred at the softer base metal HS-CS. During stretch-forming deformation by Erichsen cupping tests, the dissimilar metals exhibited various operating deformation mechanisms. The formation of shear bands (SBs) and strain-induced martensite along the SBs were observed to be the biaxial strain-induced microstructural features in the MMn-SS. However, the HS-CS was deformed by the general deformation mode, i.e., dislocation-mediated plasticity.

Mechanical properties of stationary shoulder friction stir welded Aluminum alloys AA7075-T651

Abstract: The stationary shoulder friction stir welding (SSFSW) technique promotes new opportunities for welding material. In the current work, a special setup of SSFSW was designed and manufactured in only three parts according to the homemade friction stir welding (FSW) machine dimensions and specifications. This setup with minimum parts is easily adjustable beside it facilitates fast control of the tool pin length. This gives the design more advantages than the previous designs published for the same purpose. Two different parameters were used with the SSFSW setup to butt weld samples of AA7075-T6 of 5 mm thick. Various welding travel speeds of 25, 50 mm/min to 75 mm/min and different values of Z-force of 20, 25 KN, and 50 KN were used to evaluate the effect of the SSFSW parameters on the joints quality and properties. The results confirmed that sound joints were produced without internal or surface defects. In addition, the joints are characterized with a smooth surface finish compared to the conventional FSW joints. A narrow heat affected zone around the nugget due to the elimination of heat generation by the shoulder. The tensile strength of welded samples increases with increasing the vertical force with the maximum tensile strength of 418.7 MPa at a rotational speed of 600 rpm, a welding speed of 50 mm/min, and 50 KN Z-force. This implies that the vertically applied force upon SSFSW is an important parameter in controlling the joint properties. Analysis of the hardness distribution across the weld cross-section shows a slight reduction in the heat-affected zone.

The tensile properties of 2219 aluminum alloy plate butt joint welded by novel laser mirror welding

Abstract: • A novel laser mirror welding method which can reduce deformation is proposed. • The microstructure of laser mirror welding shows an asymmetrical distribution under the action of gravity. • Under the dual action of laser heat input and gravity, the effective bearing area of the weld near the upper fusion line is the smallest, which is prone to fracture. For thicker weldments, penetration requires higher welding heat input. The significant difference in temperature between the front and back of the weldment will inevitably produce more significant welding distortion. The symmetrical double laser heat sources act on the flat plate butt joint structure during the laser mirror welding process, which can realize the deformation-free and high-efficiency welding of thick plates. Due to the particular welding method of laser mirror welding, there are complex interactions of double keyholes and double-sided joint pools during the welding process. However, there is no relevant research on laser mirror welding of aluminum alloys. Therefore, experimental analysis on laser mirror welding of the 2219 aluminum alloy is performed in this paper. The relationship between welding process parameters and weld bead formation is explored by quantitative research about the macro morphology of the weld seam. Then, the typical microstructure distribution is studied by the microstructure of laser mirror welded joints. Finally, the tensile test experiment is performed to observe the microscopic morphology of the tensile fracture to analyze the fracture mode of the joint. This article discussed the intrinsic relationship between the stability of the molten pool and the tensile properties. The study found that when the molten pool is formed, the stability of the keyhole is the worst, and the tensile performance is poor.

Effect of Zn interlayer on friction stir butt welding of A1100 and SUS316L stainless steel

Abstract: The effect of Zn interlayer on the microstructure and mechanical properties of dissimilar A1100 and SUS316L friction stir welded (FSW) butt joints was investigated. The results showed that Zn could improve the joint’s tensile strength. However, a complete dissolution of the Zn interlayer was necessary to achieve a sound joint. During the FSW process, the stirring action of the tool dispersed the Zn into the A1100 matrix forming a solid solution of Zn. A direct relationship was found between the tool rotational speed and the Zn dissolution rate. Also, the addition of Zn inhibited the Al–Fe IMCs growth, which played a positive role in the obtained tensile strength.

Microstructure and Mechanical Properties of Dissimilar Friction Stir Welded Joint AA7020/AA5083 with Different Joining Parameters

Abstract: The present paper aims to analyze the influence of process parameters (tool traverse speed and tool rotational speed) on the macrostructure, microhardness, and mechanical properties of dissimilar friction stir welded (FSW) butt joints. Nine combinations of FSW parameters welded joints of aluminum alloys 7020-T651 and 5083-H111 were characterized. Plates in 5 mm thickness were welded using the FSW method as dissimilar joints with three values of tool rotation parameters (400, 800, and 1200 rpm) and three welding speeds (100, 200, 300 mm/min). The macroscopic observations revealed various shapes of the stir zone and defects resulting from excess and insufficient heat input. Microfractographic analysis and tensile test results showed that the samples made with the FSW parameters of 800 rpm and 200 mm/min had the best strength properties: UTS = 303 MPa, YS = 157 MPa, and A = 11.6 %. Moreover, for all welds at welding speed 100 mm/min, the joint efficiency reached 95%.

An investigation on mechanical and microstructural evolution of stationary shoulder friction stir welded aluminum alloy AA7075-T651

Abstract: The stationary shoulder friction stir welding (SSFSW) technique promotes new opportunities for welding material. In the current work, a special setup of SSFSW was designed and manufactured in only three parts according to the homemade friction stir welding (FSW) machine dimensions and specifications. This setup with minimum parts is easily adjustable beside it facilitates fast control of the tool pin length. This gives the design more advantages than the previous designs published for the same purpose. Two different parameters were used with the SSFSW setup to butt weld samples of AA7075-T6 of 5 mm thick. Various welding travel speeds of 25, 50 mm/min, and 75 mm/min and different values of Z-force of 20, 25 KN, and 50 KN were used to evaluate the effect of the SSFSW parameters on the joints’ quality and properties. The results confirmed that sound joints were produced without internal or surface defects. In addition, the joints are characterized with a smooth surface finish compared to the conventional FSW joints. A narrow heat affected zone around the nugget due to the elimination of heat generation by the shoulder. The tensile strength of welded samples increases with increasing the vertical force with the maximum tensile strength of 418.7 MPa at a rotational speed of 600 r/min, a welding speed of 50 mm/min, and 50 KN Z-force. This implies that the vertical applied force upon SSFSW is an important parameter in controlling the joint properties. Analysis of the hardness distribution across the weld cross-section shows slight reduction in the heat affected zone.

Experimental study on tensile fracture mechanism of butt joints in multi-celled CFST walls

Abstract: Multi-celled concrete filled steel tubular walls (MCFSTWs) have been widely used in engineering practice. A high MCFSTW can be constructed by assembling two medium-height wall segments that are butt welded with the connector. At the connecting part between two wall segments, the connector, welding seams and steel plates of upper and lower wall segments form the butt joint. Since the butt joint is susceptible to tensile fracture, it is necessary to investigate its tensile fracture mechanism. In this paper, 12 specimens representing different parts of the butt joint are tested under tension and they include 6 types with different configurations. These specimens are designed by using connectors with different shapes and considering different welding conditions. The test results are analyzed and validated against the numerical simulation considering the ductile damage criteria. Based on the reliable finite element (FE) model, a simplified model is established to study the fracture performance of the complete butt joint. Finally, reliable design recommendations based on the experimental results and supplement FE analysis are summarized for improving the tensile performance of butt joints in MCFSTWs.

Homogenizing the intermetallic compounds distribution in Al/Cu dissimilar friction stir welding joint with the assistance of ultrasonic vibration

Abstract: In this work, plates of dissimilar Al/Cu alloys were butt jointed by friction stir welding (FSW) with and without ultrasonic vibration. It was found that the assistance of ultrasonic vibration produced slight variations of both mechanical interlocking and material intermixing of dissimilar material, as well as fracture location during tensile tests, but it particularly reduced the thickness of intermetallic compounds (IMCs) layer in the middle part of the Al/Cu joint. Therefore, by homogenizing the IMCs distribution along the bonding interface within a thickness of 1.0 µm, the tensile strength of the Al/Cu FSW joint was improved from 195.5 to 215.0 MPa with the assistance of ultrasonic vibration.

Statistical Characterization of Stress Concentrations along Butt Joint Weld Seams Using Deep Neural Networks

Abstract: In order to ensure high weld qualities and structural integrity of engineering structures, it is crucial to detect areas of high stress concentrations along weld seams. Traditional inspection methods rely on visual inspection and manual weld geometry measurements. Recent advances in the field of automated measurement techniques allow virtually unrestricted numbers of inspections by laser measurements of weld profiles; however, in order to compare weld qualities of different welding processes and manufacturers, a deeper understanding of statistical distributions of stress concentrations along weld seams is required. Hence, this study presents an approach to statistically characterize different types of butt joint weld seams. For this purpose, an artificial neural network is created from 945 finite element simulations to determine stress concentration factors at butt joints. Besides higher quality of predictions compared to empirical estimation functions, the new approach can directly be applied to all types welded structures, including arc- and laser-welded butt joints, and coupled with all types of 3D-measurement devices. Furthermore, sheet thickness ranging from 1 mm to 100 mm can be assessed.

The role of thermal contribution in the design of AA2024 friction stir welded butt and lap joints: mechanical properties and energy demand

Abstract: Although in recent times the use of solid-state welding processes as friction stir welding (FSW) has become increasingly widespread, for some joint morphologies, as lap joints, there are still significantly less data available on both process parameters optimization and energy consumption. In the present paper, the authors investigated the possibility of enhancing the joint quality in two different configurations, i.e. lap and butt joints, taking into account specific thermal contribution (STC) conferred to the weld. Strength, micro-hardness and microstructure were evaluated on the produced AA2024 aluminum alloys butt and lap joints. The surface response method (RSM) was used to investigate the effects of the main process parameters and to identify optimal technological parameters in terms of joint resistance, while the specific energy consumption (SEC) of the entire process was acquired with the aim to provide design guidelines taking into account, at the same time, mechanical performance and environmental impact. It was found that the same optimal range of revolutionary pitch can be identified for both the configurations. Additionally, maximizing welding speed, for a given revolutionary pitch, contributes to significantly reduce the environmental impact of the process with no detrimental effect on the joint performance.

The role of thermal contribution in the design of AA2024 friction stir welded butt and lap joints: mechanical properties and energy demand

Abstract: Although in recent times the use of solid-state welding processes as friction stir welding (FSW) has become increasingly widespread, for some joint morphologies, as lap joints, there are still significantly less data available on both process parameters optimization and energy consumption. In the present paper, the authors investigated the possibility of enhancing the joint quality in two different configurations, i.e. lap and butt joints, taking into account specific thermal contribution (STC) conferred to the weld. Strength, micro-hardness and microstructure were evaluated on the produced AA2024 aluminum alloys butt and lap joints. The surface response method (RSM) was used to investigate the effects of the main process parameters and to identify optimal technological parameters in terms of joint resistance, while the specific energy consumption (SEC) of the entire process was acquired with the aim to provide design guidelines taking into account, at the same time, mechanical performance and environmental impact. It was found that the same optimal range of revolutionary pitch can be identified for both the configurations. Additionally, maximizing welding speed, for a given revolutionary pitch, contributes to significantly reduce the environmental impact of the process with no detrimental effect on the joint performance.