Showing papers on "Butt welding published in 2021"

Enhancing metallurgical and mechanical properties of friction stir butt welded joints of Al–Cu via cold sprayed Ni interlayer

Abstract: Intermetallic compounds (IMCs) formation is a key factor which limits the strength of dissimilar friction stir welded joints. To suppress the formation of brittle phases at the interface, a cold sprayed Ni interlayer was introduced to the copper surface before applying friction stir butt welding of Al alloy to Cu. The results indicated that when no Ni interlayer was added, the IMCs formed at the interface were Al2Cu and Al4Cu9, each of which had a thickness of ~0.6 μm. When a Ni interlayer was used, a single Al3Ni2 layer was generated with a thickness of ~200 nm. With the addition of Ni interlayer, the average tensile strength of the joint was increased from 152 MPa to 190 MPa. The joint ductility was also significantly improved from ~5.5% to ~10.5%. The improvement of ductility is a result of a fracture path change from the Al/Cu interface, to through the Al alloy stir zone instead.

Interface microstructure and tensile properties of a third generation aluminium-steel butt weld produced using the Hybrid Metal Extrusion & Bonding (HYB) process

Abstract: The Hybrid Metal Extrusion & Bonding (HYB) process is a patented solid state joining method for metals which utilizes filler material additions to consolidate the weld. In the present investigation the interface microstructure and tensile properties of a 4 mm thick joint, belonging to the third generation Al-steel HYB butt welds, are characterized. The mechanical testing shows that the HYB weld exhibits excellent tensile properties, displaying ultimate tensile strength values in the range from 238 to 266 MPa. Moreover, supplementary digital image correlation analysis of the strain evolution occurring during tensile testing reveals that all plastic deformation is localized to the soft heat-affected zone on the aluminium side of the joint, leading to necking and final fracture in the aluminium. Scanning and transmission electron microscopy examinations of the Al-steel interface show that bonding occurs by a combination of microscale mechanical interlocking and intermetallic compound formation. The intermetallic layer has a thickness varying between 0.1 and 1 μm and is composed of Al–Fe–Si crystals. This makes the butt joint highly resistant against interfacial cracking. The subsequent benchmarking against commercial fusion and solid state welding methods reveals that the tensile properties of the Al-steel HYB weld even surpass those reported for comparable friction stir welds. At the same time, the HYB process allows butt welding to be performed at much higher speeds compared to friction stir welding, without compromising the mechanical integrity of the weldment.

Pulsed laser butt welding of AISI 1005 steel thin plates

Abstract: Pulsed laser welding is a joining process, which takes advantage of the laser energy quality with precise control equipment. Its characteristics allow joining thinner materials with reduced thermal distortion without filler material, fulfilling the industrial interest in this process. In the present work, AISI 1005 steel sheets of 1.7 mm thickness were subjected to different pulse Nd:YAG laser treatments to obtain one side bead-on-plate weld samples and double sided butt welds. Since the quality of the joints is strongly influenced by the process parameters, an experimental design methodology was adopted to define a suitable combination of the laser beam power, pulse duration and spot diameter. The Box-Behnken technique and response surface methodology associated with analyses of defects allowed the determination of the appropriate welding parameters. The microstructure characterisation revealed the melted fusion zones originated from the thermal effect of the overlapped pulses. Additionally, microhardness measurements at fusion zone exhibited higher values than the base material and heat affected zone, due to the hard microconstituents developed. The tensile test performed at samples extracted from double sided laser welds showed good resistance results, fracturing at the base material of joints. The present work demonstrates that pulsed laser welding methodology is suitable to obtain high quality joints of steel thin plates.

Narrow gap deviation detection in Keyhole TIG welding using image processing method based on Mask-RCNN model

Abstract: In the process of K-TIG deep penetration welding, the workpiece does not need to be bevelled; therefore, the welding method is butt welding, and the gap to be welded is very narrow (0.2~1 mm). Because of the large welding current, the welding arc light intensity is very strong. These factors cause difficulties in the K-TIG weld seam tracking process. To realize weld seam tracking in the K-TIG welding process, it is necessary to extract the keyhole entrance centre and weld centreline accurately. To reduce the interference of strong arc light in the process of K-TIG welding, the information of keyhole entrance and weld seam in the process of K-TIG welding is obtained by using a high-dynamic-range camera. An image processing algorithm based on Mask-RCNN is proposed to extract the centre of the keyhole entrance accurately. An image processing algorithm based on Hough line fitting is used to accurately identify the weld centreline in the welding image and extract the welding deviation. In welding experiments, it is verified that the welding deviation extracted by the method proposed in this paper fluctuates within ± 0.133 mm, which meets the requirements of actual K-TIG welding seam tracking.

A Review of Technologies for Welding Magnesium Alloys to Steels

Abstract: We survey various state-of-the-art methods for welding magnesium alloys and steels using different joint configurations. Microstructural characterizations indicate that four microstructures may form at the Mg/steel interface after welding: unwelded gap, metal oxides, solid solutions, or intermetallic compounds. Reaction products at the Mg/steel interface vary with different welding methods, alloying elements in base materials, interlayers or coatings applied, and preparations of base material before welding. Mechanical property characterizations, (a) lap tensile shear testing for lap-welded and spot-welded joints, (b) tensile testing for butt-welded joints and (c) fatigue properties of lap-welded and spot-welded joints are summarized and compared, separately. Reaction products at the Mg/steel interface are correlated with mechanical properties. Finally, ways to enhance Mg/steel joint strength, such as introducing interlocking features during friction stir lap and butt welding, are discussed.

Identification of butt welded joint penetration based on infrared thermal imaging

Abstract: In the gas metal arc welding (GMAW) process, the intense arc light and high temperature conditions bring great difficulties to the online identification of welded joint penetration. At present, visual sensing method and arc sound detection method are mainly used to identify the welded joint penetration, there are few reports about using welding temperature field to identify welded joint penetration. In this paper, a method of using infrared thermal imaging to identify the welded joint penetration was proposed, a single infrared thermal imager was used to monitor the welding temperature field in real time, the solidified weld area outside the weld pool area was selected as the region of interest (ROI) for real-time temperature measurement. The temperature field distribution features of ROI were extracted, taking these features as input and welded joint penetration as output, the identification model for welded joint penetration was established based on artificial neural network (ANN). The identification accuracy and generalization ability of the identification model were verified by a variety of butt welding experiments, the experimental results show that the identification accuracy of the established model for three penetration states of welded joint is higher than 96%, which can be applied in the online identification of welded joint penetration.

Friction Stir Spot Butt Welding of Dissimilar S45C Steel and 6061-T6 Aluminum Alloy

Abstract: Friction stir spot welding (FSSW) of dissimilar S45C steel and 6061-T6 aluminum alloy in a butt configuration is experimentally investigated. Butt spot welding is performed using a convex scrolled shoulder tool at different tool rotational speeds. FSSW butt joints are successfully fabricated by offsetting the tool to the steel side. The microstructures of the joints fabricated at three different tool rotational speeds are characterized using scanning electron microscopy and energy dispersive spectrometry. Microstructural analysis shows the presence of intermetallic compounds (IMCs) along the steel/aluminum interface. The thickness of the IMC layer and the tensile strength of the joint increase with increasing the tool rotational speed. The results of tensile tests and microstructural analysis show that the joint performance is closely related to the IMCs at the joint interface.

Influence of thermo-mechanical material properties on the structural response of a welded butt-joint by FEM simulation and experimental tests

Abstract: This paper deals with the development of a Finite Element (FE) model for the simulation of a two-passes V-groove butt weld joint. Specifically, in order to reduce the computational costs and the efforts aimed to the numerical evaluation of residual stresses distribution in welded joints, a sensitivity analysis has been performed to quantify the level of accuracy provided by the model when the strict dependence of some material properties on the temperature is neglected. Before proceeding with the sensitivity analysis, the reliability of the proposed FE model was assessed against an experimental test; a good agreement between numerical and experiment results has been achieved. In detail, the material properties involved in this sensitivity analysis are: thermal conductivity, specific heat, Young's modulus and thermal expansion coefficient; the investigated outputs are: temperatures, residual stresses, displacements and angular distortion. Several test cases have been simulated by considering all of these material properties as constant, one at a time or all together. The results analysis showed that the levels of accuracy provided by the different simplifications depend on the selected output. Among the most relevant results, it has been found out that the predicted temperatures distributions are not significantly influenced by the considered material simplifications. The effects on the residual stresses in considering the thermal conductivity and the specific heat as constant are negligible. The hypothesis of a constant thermal expansion coefficient provides an acceptable level of accuracy only in proximity of the weld seam. Finally, concerning the displacements field and the angular distortion of the welded plates, by considering the thermal conductivity and Young's modulus as constant, the effectiveness of the model appears to be compromised.

The effect of laser beam intensity distribution on weld characteristics in laser welded aluminum alloy (AA5052)

Abstract: The distribution of laser beam intensity can play a key role in laser welding, since it is deeply related to the temperature gradient and cooling rate of the melt pool In this study, aluminum alloy butt welding was conducted using a normal Gaussian beam and modulated beams with various intensity profiles, produced with a diffractive optical element (DOE) Their effect on the weld characteristics was investigated Welding with the modulated beams generally required larger heat input for full penetration compared with the Gaussian beam welding (GBW) since laser energy was spread by the core and ring beam combination This laser energy spreading reduced weld defects and produced a funnel-shaped weld cross-section in the modulated beam welding (MBW) Microstructure analyses found that the GBW and MBW had different grain growth behaviors based on the shape of the melt zone boundary A straight melt zone boundary formed along the vertical direction induced columnar grain growth along the horizontal direction in the GBW For the MBW, it grew along the diagonal direction, because the melt zone boundary had a slanted shape The highest tensile strength (2082 MPa, which corresponded to ~ 91% of the tensile strength of the base material) was obtained with the MBW, owing to reduced average grain size It was found that the re-crystallization process induced by laser welding significantly increased the grain size of the original material

Effect of preheating on joint quality in the friction stir welding of bimodal high density polyethylene

Abstract: The effect of process temperatures on joint quality in friction stir butt welding of bimodal high density polyethylene (HDPE) was investigated. Process temperatures were manipulated by varying the rotation speed and welding speed. Further control of the process temperatures was achieved by heating the bottom side of the welded plates using a film heater. Temperatures on the top and bottom surfaces of the welded plates were measured by infrared thermography and thermocouples, respectively. Material flow patterns were also visualized by implementing a novel welding technique where two different colors of HDPE were placed on the advancing and retreating sides, respectively, and the cross section of the welding zone was inspected after welding. It was found that proper welding of this bimodal HDPE takes place when the material is maintained at high enough temperatures in the viscous state throughout its thickness. Under these conditions, proper interphase mixing and fusion of the material takes place. Weld efficiencies in excess of 100% and large elongations in the order of 60% were also obtained at the optimum range of welding temperatures.

Residual Stress Study of High Manganese Steel Riser Pipe Manufactured by Longitudinal Butt Welding (1) : Residual Stress Measurement and FE Analysis

Abstract: In recent years, the deep and ultra-deep seas are recognized as the last remaining regions on the planet where oil and natural gas resources are discovered and produced. In order to develop such natural resources in an environmentally safe and cost-effective method, various engineering systems and technologies are being developed. In keeping with this direction of development, there is significant worldwide interest among major offshore structural and system operators in examining the possibility of using high-strength steel for long-distance gas transmission pipelines and risers. In particular, riser pipes using high manganese steel are often made by longitudinal butt welding, In order to make a riser, which is a large pipe structure, it is necessary to do pipework to bend the plate. At this time, welding is required in the longitudinal direction of the riser, and this welding is the longitudinal butt welding. But studies related to the prediction of residual stresses for this are insufficient. In this paper, the residual stress values ​of longitudinal butt welding of high manganese steel using the hold drilling method were measured. Furthermore, the residual stresses in various directions were calculated using a precise thermal-elastic analysis technique, and comparative verification with the measured values ​was conducted to see if this method is valid as a residual stress prediction method.

Investigation on microstructure and mechanical properties of double-sided synchronous TIP TIG arc butt welded duplex stainless steel

Abstract: Double-sided synchronous TIP TIG arc butt welding (DSSTTABW) is firstly carried out to join 5-mm SAF 2205 duplex stainless steel (DSS) plates without grooving. The microstructure and mechanical properties of DSSTTABW joints, including microhardness, transverse tension, and bend properties, are evaluated systematically. Results show that sound DSS joint, with excellent appearance and properties, can be obtained through the DSSTTABW process. In DSSTTABW joints, a deal of second austenite (γ2) appears in the weld metal, resulting in a slight increment of austenite volume fraction of the weld zone. Meanwhile sigma (σ) phase precipitates at the grain boundaries of delta ferrite (δ-Fe) and austenite of the weld zone. Mechanical property tests show that the DSSTTABW weldment exhibits higher tensile strength and microhardness but lower ductility compared to 2205 DSS base metal due to the existing Widmanstten-type austenite (WA) and σ phase. All weldments fracture at the weld zones in the mode of ductile. After bending tests, no surface cracks are observed on the DSSTTABW joint.

Mechanical properties and microstructure of multi-pass butt weld of plates made of Al-Mg-Zr alloy sparingly doped with scandium

Abstract: Aluminum alloys doped with scandium represent a new generation of high-performance alloys that have numerous advantages compared to high-strength aluminum alloys. However, the cost of such alloys is quite high. Thus, scientists have been searching for new alloys sparingly doped with Sc that are suitable for industrial use. The current research aims to study the mechanical properties and microstructure of a multi-pass butt-welded joint of plates made of 1580 alloy of the Al-Mg-Zr system sparingly doped with Sc 0.1 wt%, depending on the shape of a weld groove and the chemical composition of the filler wire. Welding of plates with a thickness of 34.5 mm with X-groove and K-groove was performed by the TIG method in manual mode with filler wires from aluminum alloys. Good weldability and hot crack resistance of 1580 alloy providing ultimate strength of welded joints at the level of 0.84–0.93 of the ultimate strength of the base metal were established. The peculiarity of the thermal cycles of multi-pass welding affects the structure formation. The formed coarse-crystalline structure of the weld from 1580 filler wire leads to reduced mechanical properties of the welded joints, compared to the welded joints obtained with the use of 1561 filler wire. The analysis of the macro- and microstructure of the welded joints is given. The results of SEM and EDS studies of welds are presented.