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Vertical oscillation arc welding for narrow gap gas metal arc welding (NG-GMAW) has a relatively simple structure, and it is widely used in all-position pipeline field welding. However, it has some shortcomings, such as incomplete fusion defects on the sidewall and interlayer. Aiming at resolving these shortcomings, a mathematical model is proposed to obtain appropriate welding parameters in different positions. In this model, the response surface methodology (RSM) based on the central composite design (CCD) was developed to study the interactions between welding parameters and the weld bead geometry. Then the analysis of variance (ANOVA) was used to evaluate the accuracy and significance of the proposed model. Finally, experiments were carried out in flat, vertical, and overhead positions to obtain the optimal parameters. The macroscopic metallography of the transversal section of the weld bead under the optimizing welding parameters showed that the weld beads were free of defects in the sidewall and interlayers. [ABSTRACT FROM AUTHOR]

Thick-walled X80 pipelines for oil and gas transportation are difficult to relocate due to their large size. In the process of narrow-gap overhead welding, welding defects, such as bulges and lack of sidewall fusion, can appear easily. To avoid these defects and to improve the welding quality of thick-walled pipelines, the GMAW welding method is adopted in this paper. The formation characteristics of the weld and the influence of arc oscillation parameters, such as the oscillation width and sidewall dwell time, on the formation process of narrow-gap overhead welding seams are studied. In this research, it was found that, in the NG-GMAW overhead welding position, there was a downward trend in the middle of the formed surface of the weld pool. Defects, such as finger-shaped penetrations and lack of sidewall fusion, were prone to occur due to gravity. The increased oscillation width was beneficial for reducing the protrusion in the middle of the weld seam, but an excessive oscillation width can easily cause undercut defects. The sidewall dwell time has little effect on the protrusion in the middle of the weld seam, but it can increase sidewall penetration, thereby avoiding the occurrence of incomplete sidewall penetration. [ABSTRACT FROM AUTHOR]

• Laser welding of TC4 alloy to 304 SS using Cu interlayer and Cu-Zn filler was studied. • A composite joint based on different connection mechanisms is proposed. • The unmelted Cu acts as a barrier to the mixing of the base materials. • The unmelted Cu prevented the formation of brittle Ti-Fe intermetallics in the joint. A Cu interlayer and Cu-Zn filler metal were used for laser brazing of TC4 alloy to 304 stainless steel (SS). To avoid the formation of brittle Ti-Fe intermetallics, a new welding procedure for SS-Ti alloy joints was proposed. The laser beam was focused on the steel plate 0.3 mm away from the Cu interlayer for controlling Cu partial melting. The Cu-Zn filler melted occurred at the Cu-Ti interface through the heat transfer of unmelted Cu. The brazed weld with the main structures of α-phase (Cu, Zn), α-Cu, CuTi + Ti 2 Zn. At the brazed weld-TC4 alloy interface, the joint fractured with a maximum tensile strength of 108 MPa. [ABSTRACT FROM AUTHOR]

• MXene composite materials were prepared with classical hydrothermal method. • MXene composites were used as the performance enhancers for conductive adhesives with silver-coated copper fillers. • The addition of the two-dimensional Ti 3 C 2 T x composite connects the originally point-contact and disconnected Ag-clad Cu. Ti 3 C 2 T x /Ag/Cu composite conductive filler and silver-plated copper powder powder were used as performance enhancers for the conductive binder. The dendritic silver-plated copper powder powder is uniformly dispersed in the resin matrix, and its unique morphology makes it easy to contact with each other and form a conductive network, which provides a pathway for carrier transfer. In this study, it was found that the volume resistivity was 4.32 × 10−4 Ω·cm when the content of Ti 3 C 2 T x /Ag/Cu was 0.5 %, which indicated that the modified MXene synergized with the silver-plated copper powder powders contributed to the reduction of the volume resistivity of the ECAs (electrically conductive adhesives). [ABSTRACT FROM AUTHOR]

• The effective joint for 7075/D6AC direct laser welding is obtained by laser welding. • Microcracks, pores and Fe 2 Al 5 , Fe 3 Al, FeAl 3 exist in the joint. • The tensile strength of the joint is about 2–3 times that of the general joint. • The fuse line on the aluminum side is the weak area of the joint. By direct laser welding, 7075 super-hard aluminum and D6AC super-high strength alloy structural steel were joined together. In order to determine joint microstructures, Energy dispersive spectroscopy (EDS), Scanning electron microscopy (SEM) were used. To find out the mechanical properties of the joints, tensile tests were performed. The results showed that when the laser beam offset was centered on the contact surface of 7075/D6AC, the welding speed was 650 mm/min, the laser power was 396 W, and the defocusing distance was +5 mm, the joints were best formed. In the joints, brittle intermetallic compounds FeAl 3 , Fe 3 Al, and Fe 2 Al 5 were formed. The joint fractured in the fusion line on the aluminum side with a gross tensile strength of 94 MPa. [ABSTRACT FROM AUTHOR]

• The possibility of two pass welding for Ti alloy-SS joint with TA2/Q235 as composite interlayer was studied. • The unmelted part of TA2/Q235 composite interlayer acted as a diffusion barrier between Ti and Fe. • The unmelted TA2/Q235 composite interlayer was beneficial to relieve and accommodate the thermal stress. In this work, TA2/Q235 was used as an composite interlayer to prevent the formation of these brittle Ti-Fe intermetallics when joining TC4 Ti alloy to 304 stainless steel (SS). The TA2/Q235 composite interlayer was prepared by explosive welding. The laser was focused on the TC4-TA2 interface, which joined the TC4 and TA2 by fusion welding. At TC4-TA2 interface, a weld zone was formed due to the mixing of molten TC4 and TA2. The laser was focused on the Q235-304 SS interface, a weld zone was formed due to the mixing of molten Q235 and 304 SS. Composite interlayer TA2/Q235 was used to prevent the formation of Ti-Fe intermetallics during welding and improve microstructure and properties of the Ti alloy-SS joint. The joint fractured at the TA2/Q235 explosive welding interface with the maximum tensile strength of 548 MPa. [ABSTRACT FROM AUTHOR]

• The possibility of laser welding for Ti alloy and SS joint with composite interlayer was studied. • Unmelted composite interlayer acted as a barrier to mixing of the base materials. • The unmelted composite interlayer prevented the formation of brittle Ti-Fe intermetallics in the joint. Welding is currently the most effective method of joining TC4/304SS dissimilar metals. However, due to the large differences in the physical and chemical properties of titanium/steel, direct welding produces a large number of brittle intermetallic compounds such as TiFe, Ti2Fe, etc., and the joints usually fracture on their own after welding, making it impossible to obtain safe and reliable composite joints. In this study, a composite interlayer was used to realize the TC4/304 SS joint and the effect of YZ on the mechanical properties of the joint was investigated. It was found that the tensile strength of the titanium side of the composite sandwich was 968 MPa when YZ = was 8 mm. This connection method effectively avoids the generation of brittle intermetallic compounds such as Ti-Fe, and optimizes and improves the mechanical properties of the joint to a large extent, which is of great importance to the research value. [ABSTRACT FROM AUTHOR]

• It has created a new connection mode, which perfectly combines mechanical connection and metallurgical connection. • A new welding structure is developed, which takes advantage of the advantages of two connection methods. • The possibility of laser welding-brazing for Ti alloy-stainless steel joint with Cu and screw was studied. • A composite joint based on two different joining mechanisms. • The unmelted Cu and screw prevented the formation of brittle Ti-Fe intermetallics in the joint. In this work, the machine tool machining and compound welding mechanism are combined to create a new processing technology. Dissimilar welds between stainless steel (SS) and Ti alloy were produced with mechanical joining and metallurgical joining technique. The mechanical joining of the Cu interlayer, CuZnSn filler and Ti alloy was connected by screws, and then the laser weld formed at the SS/Cu interface due to the good weldability of Fe and Cu. Brazing weld at Ti/CuZnSn interface formed through the SS side weld heat conduction, which realized the mechanical and metallurgical double joining of the SS/Ti joint and improved the strength of the joint. Unmelted Cu interlayer was retained by laser offset to the SS side to achieve heat transfer to the CuZnSn and Ti alloy. The CuZnSn filler was not melted, but the eutectic reaction with low melting point still occurred by atomic diffusion. The joint fractured at the Ti side interface with the maximum tensile strength of 199 MPa. This method combines the advantages of machine tool machining and metallurgical machining at the same time. [ABSTRACT FROM AUTHOR]

• The possibility of laser welding-brazing for TiNi alloy-SS joint with Cu-base filler metal was studied. • A composite joint based on two different joining mechanisms. • Unmelted SS acted as a barrier to mixing of the base materials. • The unmelted SS and filler metal prevented the formation of brittle Ti-Fe intermetallics in the joint. In this paper, laser welding of TiNi alloy and stainless steel (SS) dissimilar metal material with 38Zn-61Cu alloy as filler metal was carried. The results showed that the TiNi alloy and SS were joined by melting filler metal when the laser was concentrated in the SS side of the joint. One process was one pass welding involving creation of a joint with one fusion weld and one diffusion weld separated by remaining unmelted SS. When laser beam on the SS side was 1.2 mm, SS would not be completely melted in joint. During welding, the laser was focused near the TiNi alloy-SS interface, so that TiNi alloy and SS partially melted and diffusion welding process was realized at the TiNi alloy-SS interface, while element diffusion bonding occurred at the TiNi alloy-SS interface. No Ti-Fe intermetallic was detected in the joint. A diffusion weld was formed at the SS-TiNi alloy interface with the main microstructure of β-CuZn + Fe 3 Zn 7 , β-CuZn and Ti 2 Cu + TiNi. The joint fractured at the diffusion weld with the maximum tensile strength of 153 MPa. [ABSTRACT FROM AUTHOR]

• The possibility of laser welding-diffusion bonding for Ti alloy-SS joint with Ag-base filler metal was studied. • A composite joint based on two different joining mechanisms. • The unmelted SS acted as a barrier to mixing of the base materials. • The unmelted SS and filler metal prevented the formation of brittle Ti-Fe intermetallics in the joint. Laser welding of TC4 Titanium (Ti) alloy to 304 stainless steel (SS) has been applied using Ag45-Cu30-Zn25 alloy as filler metal. A new welding process for SS-Ti alloy joint was introduced on the basis of the controlling the formation of Ti-Fe intermetallics in the joint. One pass welding involving creation of a joint with one fusion weld and one diffusion weld separated by remaining unmelted SS. When laser beam on the SS side was 1.6 mm, SS would not be completely melted in joint. Through heat conduction of unmelted SS, the atomic diffusion occurred at the SS-Ti alloy interface. A diffusion weld was formed at the SS-Ti alloy interface with the main microstructure of AgZn 3 + CuZn, α-Cu + Fe 3 Zn 2 and Ti 2 Cu + TiCu. The joint fractured at the diffusion weld with the maximum tensile strength of 284 MPa. [ABSTRACT FROM AUTHOR]

• The possibility of laser welding-diffusion bonding for Ti alloy-SS joint with Ag-base filler metal was studied. • A composite joint based on two different joining mechanisms. • The unmelted SS acted as a barrier to mixing of the base materials. • The unmelted SS and filler metal prevented the formation of brittle Ti-Fe intermetallics in the joint. Laser welding of TC4 Titanium (Ti) alloy to 304 stainless steel (SS) has been applied using Ag45-Cu30-Zn25 alloy as filler metal. Microstructures of the joints were studied using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Mechanical properties of the joints were evaluated by performing tensile tests. The temperature field and stress field distributed in laser welding based on SS-Ti alloy joint were dynamically simulated using the ABAQUS in this study. A new welding process for SS-Ti alloy joint was introduced on the basis of the controlling the formation of Ti-Fe intermetallics in the joint. One pass welding involving creation of a joint with one fusion weld and one diffusion weld separated by remaining unmelted SS. When laser beam on the SS side was 1.6 mm, SS would not be completely melted in joint. Through heat conduction of unmelted SS, the atomic diffusion occurred at the SS-Ti alloy interface. A diffusion weld was formed at the SS-Ti alloy interface with the main microstructure of α-Cu + Fe 3 Zn 2 , AgZn 3 + CuZn, Cu 4 Ti + Ti 2 Zn 3 and Ti 2 Cu + TiCu. The joint fractured at the diffusion weld with the maximum tensile strength of 284 MPa. By comparing the simulation results with the corresponding experimental findings, the validity of the numerical model is confirmed. [ABSTRACT FROM AUTHOR]

• The possibility of laser welding-brazing for Ti alloy-SS joint with Cu-base filler metal was studied. • A composite joint based on two different joining mechanisms. • Unmelted SS acted as a barrier to mixing of the base materials. • The unmelted SS and filler metal prevented the formation of brittle Ti-Fe intermetallics in the joint. Laser welding-brazing of TC4 Titanium (Ti) alloy to 304 stainless steel (SS) has been applied using 38Zn-61Cu (wt%) alloy as filler metal. A new welding process for SS-Ti alloy joint was introduced on the basis of the controlling the formation of Ti-Fe intermetallics in the joint. One process was one pass welding involving creation of a joint with one fusion weld and one brazed weld separated by remaining unmelted SS. When laser beam on the SS side was 1.5 mm, SS would not be completely melted in joint. Through heat conduction, the filler metal melted occurred at the SS-Ti alloy interface. A brazed weld was formed at the SS-Ti alloy interface with the main microstructure of (Fe, Zn) + Fe 3 Zn 7 , β-CuZn and β-CuZn + Ti 2 Zn 3. The joint fractured at the brazed weld with the maximum tensile strength of 210 MPa. [ABSTRACT FROM AUTHOR]

This paper comparatively investigates the arc plasma morphology and the droplet transfer behavior and Characteristic of electrical signal between the pulsed MAG welding and the medium and low power laser assisted pulsed MAG hybrid Welding. Compared with the pulsed MAG welding, the assisted laser acts on the substrate before the arc to generate a stable keyhole and mass metallic vapor is generated near the keyhole leading the expansion of arc plasma morphology. The arc plasma appears obvious compression phenomenon under the action of medium power assisted laser. In addition, the keyhole has an attractive effect on the discharge channel and the height of the discharge channel becomes shorter, which makes the arc initiation stage more stable. The contact area between the arc root and the workpiece is expanded, in addition the laser has a compression effect on the arc, making the arc energy density higher and the energy use more efficient. The acting of assisted laser increased the droplet transfer frequency with the power increases, which essentially changes the electromagnetic force acting on the droplet. Others, the range of welding voltage distribution and the probability of high voltage distribution are reduced, and the transition is more stable. [ABSTRACT FROM AUTHOR]

• The possibility of laser welding-brazing for Ti alloy-stainless steel joint with Monel 400 interlayer was studied. • A composite joint based on two different joining mechanisms. • The unmelted stainless steel and filler metal prevented the formation of brittle Ti-Fe intermetallics in the joint. Joining of titanium (Ti) alloy and stainless steel (SS) was of great interest for applications in the marine and aerospace fields. Despite the importance, no joining techniques have been developed that avoid the formation of brittle intermetallic compounds (IMCs) to produce high strength joints and ensure good corrosion resistance. Successful joining of Ti alloy and SS was performed by inserting Monel 400 interlayer in this work. Ni and Cu elements in Monel improved corrosion resistance of joints. When the laser focused on the SS side to form an independent molten pool, the diffusion bonding between the Ti alloy and the SS was realized through the heat conduction of the unmelted SS. The presence of the Monel 400 interlayer was performed ensured that crack free welds were obtained and no brittle IMCs were observed. Unmelted SS was retained by laser offset to the SS side to achieve heat transfer to the Monel 400 interlayer. The Monle 400 interlayer was not melted, but the eutectic reaction with low melting point still occurred by atomic diffusion. The simulation results showed that the interface temperature could be directly controlled by controlling the welding power, and the simulation results were similar to the measured temperature. The diffusion of Ti, Cu and Ni at the Ti/Monel interface formed an obvious reaction layer composed of NiTi and CuTi. It was found that no Ti-Fe IMCs were found. The joint fractured at the Ti-SS interface with the maximum tensile strength of 132 MPa. [ABSTRACT FROM AUTHOR]

• The laser-induction heating welding technology was used for the butt of CP-Ti/304 stainless steel and CP-Ti/T2 bimetallic sheets. • The liquid mixing of dissimilar metals was avoided and Ti-Fe intermetallics cannot be formed in the joint. • The maximum tensile strength was ascertained to be 600 MPa. In this work, the CP-Ti/304 stainless steel (SS) and CP-Ti/T2 bimetallic sheets were implemented successfully using laser-induction heating welding technology without the Ti-Fe and Ti-Cu brittle intermetallics was formed in the joint. The CP-Ti of parent layer metal was welded by laser, the 304 SS and T2 of flyer layer metal were connected by induction heating welding. The induction heating welding have the advantages of only the BCuP-2 wire was melted with low heat input and the specimen of welding experiment was without heated. As the melt point of BCuP-2 wire was 710–800 °C, lower than the melt point of flyer layer metal 304 SS (1454 °C) and T2 (1083 °C) and the parent layer metal CP-Ti (1660 °C). When the process of induction heating welding, the parent and flyer layer metal was not melted and only the BCuP-2 wire was melted and filled the groove. Thus the dissimilar metals mixing was avoided completely, the Ti-Fe intermetallics without formed. The narrow transition layer was formed between the laser weld zone (WZ 1) and the induction heating weld zone (WZ 2) with the main structures of Cu, Cu 3 P and α-Ti. The joint was fractured at the WZ 1 and the 304 SS side of WZ 2 with a maximum tensile strength was ascertained to be 600 MPa. [ABSTRACT FROM AUTHOR]

• Using laser-MIG arc tandem welding technology successfully realized the butting of CP-Ti/304 SS bimetallic sheets. • The liquid mixing of dissimilar metals was avoided and Ti-Fe intermetallics cannot be formed in the joint. • The maximum tensile strength of the joint is 680 MPa. • Relative independence of upper and lower molten pool can help to reduce or eliminate the residual welding stress of the joint. In this study, CP-Ti/304 stainless steel (SS) bimetallic sheets were prepared without the formation of Ti-Fe intermetallics in the joint. This required preparing a groove in the flyer and parent layer, and melting S211 wire using laser-MIG arc welding in tandem. The laser was used for the parent layer metal (CP-Ti) and the MIG arc was used for melting the S211 wire and filling the flyer layer groove. As the melting points of the parent layer metal CP-Ti (1660 °C) and the flyer layer metal 304 SS (1454 °C) were higher than the fill wire S211 (965–1035 °C), the parent and flyer layer metals were joined without melting. Liquid mixing of dissimilar metals was avoided and Ti-Fe intermetallics were not formed. The joint was observed to fracture at the laser weld zone and the right side of MIG arc weld zone, with a maximum tensile strength of approximately 680 MPa. [ABSTRACT FROM AUTHOR]