Dissimilar Metal Joining Research Articles

Achieving superior strength and elongation from electrically assisted pressure joining of medium entropy alloy and Ti-6Al-4V

In the present study, two dissimilar alloys (Ti-6Al-4V and NbTiZr(MoTa)0.1) are joined using electrically-assisted pressure joining. This joining technique can produce components with superior mechanical properties (with a yield strength of ∼980 MPa and elongation of ∼10.5%), ensuring optimal performance under severe operating conditions. A detailed analysis of the joined interface related to phase analysis and mechanical mapping elaborated a strong joint having a high yield strength without any post-heat treatment. The findings of the present study contribute to the broader field of dissimilar metal joining and can serve as a reference for future research and development in the aerospace industry. This study demonstrates the feasibility of achieving strong and ductile solid-state joints between dissimilar alloys.

Improving strength and toughness of Ti–6Al–4V alloy/pure copper diffusion bonded joint with VCrAl1.86Ni1.86 eutectic medium-entropy alloy interlayer

To solve the metallurgical incompatibility of titanium alloy/copper dissimilar metal joining, a suitable interlayer was used to adjust the interface structure, achieving the strength and toughness of joint. The vacuum diffusion bonding between Ti–6Al–4V alloy (TC4) and pure copper (T2) with VCrAl1.86Ni1.86 eutectic medium entropy alloy (EMEA) foil was investigated. Ti3Al, Al(V, Cr)Ti2, Al(V, Cr, Ni)Ti, and AlNi2Ti phases formed in the TC4/EMEA interface. FCC and BCC double-phase solid solution appeared in the EMEA/T2 diffusion zone, resulting in the high-entropy seam between VCrAl1.86Ni1.86 interlayer and T2. The maximum shear strength of joint made at 880 °C for 90 min reached 215 MPa. The growth activation energy of reaction layers (I-III) in the TC4/EMEA interface were 283 kJ/mol, 379 kJ/mol and 431 kJ/mol, respectively. The Ti3Al/Al(V, Cr)Ti2/Al(V, Cr, Ni)Ti/AlNi2Ti interface was coherent. Nevertheless, the AlNi(V, Cr)2/Al(Cu, Ni)2 and AlNi(V, Cr)2/FCC-Cu interface was non-coherent with high strain energy. All joints broke through the EMEA/T2 interface during test. The fracture surface presented some cleavage ravines and auspicious cloud features. This study provided an effective strategy for the joining of titanium alloy and copper in high precision components of aerospace engines.

The Effect of Tool Rotation Speed on the Formation of Eutectic Structure during Friction Stir Welding of Aluminum to Magnesium

Friction stir welding (FSW) is a solid-state welding process capable of joining a wide range of light metals. However, liquation and solidification may occur during joining of dissimilar metals which leads to eutectic formation. This article aims to discover the influence of tool rotation speed on the formation of eutectic structure during friction stir welding of aluminum to magnesium. To do so, friction stir welding was performed at 600 and 950 rpm to join pure aluminum and ECO-AZ91 magnesium alloy in a lap configuration. In order to investigate the influence of the welding speed, the welding speeds of 23.5 and 37.5 mm/min were also chosen. Scanning electron microscopy (SEM) was used to study the microstructure of the joints. A shear-tensile test was used to evaluate the joints’ strengths. The fracture surfaces were also studied by SEM. The results revealed that changing the rotation speed directly affects the eutectic formation, whereas the welding speed had no influence. A lower rotation speed resulted in a thin, continuous intermetallic layer, whereas a higher speed led to the formation of a massive Mg-Al12Mg17 eutectic microstructure. The formation of eutectic, as an indicative of liquation, may affect the material flow during the process due to decreasing the friction coefficient between the tool and material. The macrostructure analyses showed that the phase evolution as well as the mechanism of material flow are highly affected by liquation.

A parametric study on the mechanical properties of MIG and TIG welded dissimilar steel joints

In the present day, the joining of dissimilar metals used in the same industry applications is of great interest. MIG and TIG welding processes are among the most common methods used to join dissimilar metals with high strength and reliability. Due to the different mechanical properties of dissimilar metals to be joined by these welding methods and welding parameters, they must be carefully selected. In this study, the effects of Total Accumulated Weld Volumes (TAWV) and different groove angles (45°, 60°, 75° and 90°) on the mechanical properties of AISI 1040 and AISI 8620 cylindrical steel joints were investigated experimentally. In addition, the fracture surfaces of the samples were examined by scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX). In the process with MIG and TIG welding, only current and voltage changes were made in order to measure the effects of parameters on the mechanical properties of the joints more clearly. As a result of the studies, the highest average Ultimate Tensile Strength (UTS) was 579.611 MPa and the lowest average UTS value was 424.611 MPa. Based on TAWVs, the highest average UTS value was obtained in TIG welded joints, and the lowest average UTS value was obtained in MIG welded joints. It was observed that the UTS values of the joints were positively affected by the increase in TAWV. The UTS value of the 90° groove angled joint was found to be 40.25% higher than the UTS value of the 45° groove angled joint.

Corrosion and wear resistance of the Al/steel dissimilar weld metals by using multi-principal filler materials

Abstract Multi-principal filler materials via a high-entropy design have been reported to successfully finish the dissimilar metal joining of Al alloy to steel and to reduce the amount of Fe-Al IMCs in weld metals. However, few studies have concentrated on the corrosion and wear resistance of the Al/steel dissimilar weld metals by using multi-principal filler materials. In this study, the joining of Al 6061 alloy to 304 stainless steel served as the research object. Three types of filler materials including CoZnCuMn0.8Si0.2, FeCoCrNiMn, and AlSi12 powders were used. The effects of multi-principal filler materials on the corrosion behavior and wear resistance of the weld metals were evaluated. It was found that the weld metals by using multi-principal filler materials presented the contents of chemical elements in the range of 5–35 at%. The thermodynamic environment with a low ΔG mix was formed in the weld metals. Compared to the AlSi12 sample, the FeCoCrNiMn sample had excellent corrosion resistance in NaCl solution, whereas the CoZnCuMn0.8Si0.2 sample had excellent corrosion resistance in HCl solution. Moreover, the weld metals by using multi-principal filler materials had a better wear resistance compared to that of the AlSi12 sample. The wear loss of the CoZnCuMn0.8Si0.2 and FeCoCrNiMn samples was 4.5% and 11.4% of that of the Al 6061 alloy, respectively. Abrasive wear was the main wear mode for the weld metals by using multi-principal filler materials.

A new friction processing method for welding of dissimilar metals

A friction processing method is proposed for joining of dissimilar metals which does not involve direct mechanical processing, significant deformation or thickness reduction of parent metals. A rotating tungsten carbide tool is plunged into a sacrificial top sheet to generate heat and pressure required for dissimilar metal welding. Constant plunge rate is applied till melting initiates at the interface. Interdiffusion of dissimilar metals at the interface, results in interface melting at (near eutectic) temperatures well below the melting of either of the base metals. Once the interface starts melting, plunging is stopped and tool is maintained at constant position for a prescribed dwell time. Rapid cooling, from self quenching, occurs in the weld zone once the tool is retracted post the dwell time. In this work, the proposed method is used for lap welding of copper and aluminium sheets. While low dwell times are seen to result in insufficient bonding, excessive dwell times are seen to result in higher amounts of brittle intermetallic phases that degrade the joint strength. High bond strength is achieved for 0.05 mm/s plunge rate and 10s dwell time. Cross-sectional scanning electron micrographs, fractographs, electron dispersive spectroscopy, X-ray diffraction, mechanical strength tests, and finite element analysis are used to investigate the physics of the process and to study the effect of process conditions on resulting microstructures, phase formations and mechanical properties of the joint. The diffusion layer at the interface is predominantly composed of lamella with alternating phases of Al and Al2Cu at homogeneous eutectic composition. Very thin Cu rich transition layers are formed towards Cu side. X-ray diffraction and SEM images of fracture surfaces on Al- and Cu-side, from peel tests, show that fracture occurs in the interface layer towards the Cu side. Finite element analysis (FEA), using a fully coupled thermo-mechanical model, is used to understand the temperature evolution in the weld zone for different plunge rates. The method holds great promise for joining dissimilar metal sheets of a wide range of thicknesses.

Improved wettability of Al[sbnd]Si5 on DP980 steel during laser-induced heating by surface texture preparation

Sound wettability is the prerequisite for reliable joining of dissimilar metals. Surface textures prefabricating is a promising method to improve the surface properties of metals. Hence, surface textures with different line spacings were conducted on DP980 steel by nanosecond pulsed laser. This study investigated the laser-induced wetting behaviors of AlSi5 on surface processed DP980 steel substrates. The wettability of liquid AlSi5 presented anisotropy on textured surface, which was inhibited in perpendicular direction of the groove and promoted in parallel direction. Enhanced diffusion behavior and interfacial reaction were caused by surface textures. The absent Si-rich zone at triple lines (contact lines of solid-liquid-gas phase during wetting processes) of textured samples decreased the surface energy of droplets. Moreover, surface textures effectively reduced the normalized free energy, which provided greater driving force for spreading. However, the energy barriers caused by groove texture deteriorated the wettability in vertical direction. This method provided the possibility for the directional optimization of surface wettability, which laid the foundation for joining of dissimilar metals.

Study of joining copper-mild steel using microwave energy

In the present work, joining of dissimilar metals using electromagnetic energy has been successfully achieved. A 900 W multimode microwave applicator at the fixed frequency of 2450 MHz was used to generate the required heat energy for joining. Copper (Cu) and mild steel (MS) were chosen as the base material to be joined. Copper metal powder in the form of the thick slurry was prepared and used as a joining agent between two bulk interfaces. The joining process was carried out through the controlled emission of microwaves at a particular area for a particular period of time. Due to these controlled emissions of microwaves, the slurry of metal powder got melted and produced a fine bond with the bulk interfaces on cooling. To understand the nature of the joint formation, joints were characterized by using an optical microscope, SEM, X-ray diffractometer, microhardness tester, and Universal testing machine. Analysis of SEM resulted in a well-defined, merged, and fused joint. The microhardness at the joint zone was recorded to be 73 ± 4 HV and 78 ± 6 HV on copper side and MS side respectively. Strength test results showed the UTS of 170 MPa with 13.25% elongation.

An experimental study of friction stir welding parameters effect on joint properties of aluminium alloy and copper plate

Joining dissimilar metals like copper and aluminium is a complex area of research for the manufacturing industry. To effectively join the AA7075 with copper plates, an experimental investigation on friction stir welding was carried out. A straight cylindrical pin profile tool of H13 tool steel was chosen for this study. On the advancing direction, the AA7075 plates were fixed under the condition of zero tool offset. The tool was positioned at a 2° tilt angle for the entire experiment. Tensile test, microhardness test, SEM and EDS analysis were completed to investigate the effectiveness of the process parameters (tool traverse and rotational speed) in combination with a modified set-up on the microstructure, tensile strength and microhardness of the joint. Fractography was conducted on fractured specimens to identify the mode of failure. Complex microstructures of swirl and vortex-type material flow patterns were created in the stir zone. As a result of SEM analysis, one of the samples (S5) had finer grains at intermediate heat input, which produced excellent microhardness and tensile strength. Fractography identified ductile failure as the predominant mode of failure in the joints. The results of this study include an ultimate tensile strength value of 221.091 MPa with a joint efficiency of 95.05%, yield strength of 159.035 MPa, maximum elongation of 9.335% and a microhardness value of 271 HV for specimen welded at a traverse speed of 60 mm min−1 and a rotational speed of 1400 rpm.

Ultrasonic spot welding for joining dissimilar metals and composite materials

Ultrasonic spot welding (USW) is a solid joining technique widely known for the joining of metals and composite materials. However, joining dissimilar metals using USW introduces voids, swirl-like structures, and poor intermetallic compounds around weld interfaces. This paper examines the current state of USW for joining dissimilar metals and composite materials. Several critical issues were also discovered including technique, defect, stress distribution, and macrostructure. This review summarized the understanding of the fundamental phenomena involved in weld formation during USW of dissimilar material. Finally, the way forward in the field of spot welding is also presented.

Process-induced damage and its effect on strength of composite - aluminum alloy joint by FDS technique

Flow drilling screw (FDS) is a novel joining technique that enables high-speed joining of dissimilar metals with one-shot process of hole machining, female thread forming and fastening from one side. The damage after FDS process and its effect on joint strength and fracture behaviour near the screw by load-bearing tests for FDS joints between aluminum alloy and carbon fibre reinforced thermoplastics (CFRTP) are evaluated. Cross-sectional observation after joining process reveals that delamination in CFRTP is clearly suppressed and matrix resin is filled in the screw thread compared to the case with CFRP using thermosetting resin. In the joint strength test with shear loading and the cross-shaped tensile tests where the screw is pulled out in its axial direction, only the fibre micro-buckling is observed until fracture. These experimental results recommend that CFRTP laminates should be applied as composite side since this technique utilizes frictional heat by the screw that can contribute to plastic flow or deformation of the thermoplastic resin with high fracture toughness. It is also clarified that damage growth is further suppressed by using CFRTP/Al hybrid laminates where aluminum alloy sheets are inserted between CFRTP plies, which leads to improve the joint strength.

Force enhanced wire laser additive manufacturing of aluminum and titanium alloys

Brittle intermetallic compound formation is typically difficult to avoid during fusion joining of dissimilar metals. In this paper, a new approach called force enhanced wire laser additive manufacturing is proposed to join aluminum and titanium alloys. Ti6Al4V titanium alloy single track was additively fabricated on AA7075 plate successfully, through two liquid pools of the wire and the substrate, separated by a buckled unmelted part of the wire, leading to a mechanically interlocked interface. The effects of manufacturing parameters including laser power, wire feeding speed, scanning speed and initial contact force between wire and substrate on the surface morphology, internal interface microstructure and formation of intermetallic compounds were investigated through high-speed camera, spectrometer, laser topography, optical imaging, SEM imaging, XRD characterizations along with numerical simulations at different scales. And the maximum tensile strength reached 380 MPa in the tensile test. The experimental and numerical results indicate that the thermal modulation approach can effectively control the formation of brittle compounds between titanium and aluminum alloys and that the initial contact force ensures a good bond between the two metals.

Interfacial microstructure and mechanical properties of the Al/Ti joint by magnetic pulse welding

Magnetic pulse welding (MPW) had attracted widespread attention due to its advantages on joining dissimilar metals. In this study, the joints of Al 1060/Ti-6Al-4 V dissimilar at different discharge energies were prepared to characterize the interface microstructure and to evaluate the tensile shear properties. The MPW joint consists of an annular welded zone and a central non-welded zone. The low discharge energies lead to joints with poor quality. A small amount of intermetallic compound (IMC) TiAl3 was formed at the welding interface due to mutual diffusion. With the increase of discharge energy, the failure mode changed from welding zone fracture to base metal fracture at the weaker side (Al side). The welding interface consists of four regions: transition zone, shear wave interface zone, sine wave interface zone and flat interface zone. Element diffusion is accompanied by the formation of dislocations, stacking faults (SFs) and deformation twins, which provides sufficient strain hardening ability for the interface. According to the element distribution and phase composition analysis results in the interface, the sound Al/Ti dissimilar joints are attributed to the wavy pattern in the interface.

Investigations on the effect of standing ultrasonic waves on the microstructure and hardness of laser beam welded butt joints of stainless steel and nickel base alloy

Joining dissimilar metals with superior quality is important to provide tailored, lightweight, and cost-efficient components. Expensive and durable materials are exceptionally used where the cheaper material would not withstand the requirements. With laser beam welding, dissimilar metals can already be joined with high precision, low heat input, and a customizable mixing degree. Introducing ultrasonic excitation into the weld pool is a promising approach for further improvements like customizing the solidification morphology and avoiding weld defects. The experiments are carried out with round bars of 30 mm diameter made of 1.4301 steel alloy and 2.4856 nickel base alloy. Ultrasonic-assisted laser beam butt welding is conducted on rotating specimens with a laser beam power of 7.75 kW and a welding speed of 0.95 m/min. The specimens are evaluated by metallographic cross sections, hardness measurements, and energy-dispersive x-ray spectroscopy (EDX). The ultrasound is used to excite an eigenmode of the sample and the weld position is varied at stress- and displacement-nodes. Two different mechanisms of acoustic grain refinement are revealed. Heterogeneous nucleation is fostered in weld seams that are positioned in stress-nodes, and the fragmentation of dendrites is fostered in displacement-nodes. The welds' chemical compositions correspond to the change of solidification morphology.

Control of intermetallic compounds in Ultrasonic-Assisted Sn soldering of Mg/Al alloys

Magnesium and aluminum alloys are widely used in various industries because of their light weight and other properties. However, Mg–Al intermetallic compounds (IMCs) decrease the joint properties of Mg/Al, which limits its applications. Here, the alloys AZ31 Mg and 6061 Al are soldered together with Sn and Sn–9Zn solders though different cooling rates via ultrasonic-assisted soldering to control IMC formation and growth. Results show that this prevents formation of Mg–Al IMCs such as Al3Mg2 and Al12Mg17; however, Mg2Sn forms in the soldered joints. The Mg2Sn thickness increases with soldering temperature, which reduces joint strength. The thickness is reduced using the Sn–9Zn solder, and the effect of Zn is analyzed. With the use of water-cooling, the Mg2Sn formation and growth are inhibited, the Mg2Sn thickness is kept below 5 μm, and the shear strength peaks at 53.2 MPa. A soldering model of Mg2Sn formation is proposed to reveal the evolution and inhibition mechanism of Mg2Sn. This study well controls IMC thickness and improves joint strength, thus expanding industrial application of Mg–Al dissimilar metals and providing a feasible method for controlling IMCs in dissimilar metal joining.

Dissimilar laser lap welding of Mg and Al alloys using a CoCrFeNi medium-entropy alloy interlayer

Laser welding of Mg to Al dissimilar metals is of great significance in various industries, such as automobile, electrical, electronics, and energy systems, which promotes lightweight composite structure. However, Mg-Al intermetallic compounds (IMCs) have tremendous detrimental effects on the dissimilar metal joining of Mg to Al. In this work, dissimilar Mg/Al alloys joints with CoCrFeNi medium-entropy alloy (MEA) powders interlayer were achieved by the laser welding process, and the effect of different laser powers on the microstructure and mechanical properties of the joints was analyzed, reaching a maximum tensile shear strength of 100.12 MPa. The formation mechanism of the interface was investigated by experimental investigations and thermodynamic calculations. In addition, a numerical simulation of the laser welding process was carried out to reveal the temperature field of the molten pool and the flow change process. Based on the law of multi-component HEA phase formation, the interfacial metallurgical products were calculated and analyzed. The results of the energy dispersive spectroscopy show that the molten CoCrFeNi MEA powders reacted with Al to form Al-rich AlxCoCrFeNi phase, due to a more negative generation enthalpy compared to Mg-Al IMCs. With the increase of laser power, the Al-rich AlxCoCrFeNi phase mixed layer went through four states of agglomeration, continuity, interruption and dispersion, while the IMCs at the interface gradually increased and finally tend to be continuity. Due to the physical barrier of MEA and formation of Al-rich AlxCoCrFeNi phase, the formation of the Mg-Al IMCs phase was effectively suppressed, which improved the shear properties of the joints. The material- microstructure-property relations was established in this work, which facilitated the development of laser welding technology for Mg and Al alloys.

Microstructure and the fatigue crack propagation in the dissimilar low alloy/stainless steel GMAW welded joints

Joining dissimilar metals is a frequent task for engineers in the power industry. The resulting dissimilar joints are then critical parts of the constructions and have to be able to withstand various loads during the operation of power devices. Due to the metals dissimilarity, the interface between ferritic side and the austenitic side of the joint is considered to be a critical area regarding the joint resistance to failure under static or cyclic loading. Proper understanding of the microstructures formed at the interface is key for production of solid and reliable dissimilar joints. In the present study, two dissimilar joints were prepared by gas metal arc welding (GMAW) using different low alloy steels. The microstructure of both joints is extensively studied using electron microscopy methods, with the emphasis taken on the interface between low alloy steel and austenitic weld metal. It was shown, that the interface between low alloy steel and weld metal is not a preferential crack path in case of non-environmental fatigue crack propagation, and the cracks are rather propagating through to the heat-affected zones of the low alloy steel side of the dissimilar joint. There were recorded significant differences in the threshold stress intensity factor between two tested welded joints (5.8 MPa × m1/2 vs. 8.7 MPa × m1/2. Therefore, the choice of the low alloy steel has a significant effect on the resistance to the fatigue crack propagation, and even small differences in the microstructure of low alloy steel may affect the resistance to the fatigue crack propagation at low stress ratios of the whole dissimilar joint.

Mechanical Properties and Electrical Resistivity of the Friction Stir Spot-Welded Dissimilar Al–Cu Joints

Alternative methods for dissimilar metal joining particularly aluminium and copper have gain interest in manufacturing sectors. Friction stir spot welding was carried out on the AA6061 and C11000 wires of 2 mm diameter. This research paper reported the results on microstructures and mechanical properties of the spot-welded joints, and also special attention is provided for electrical resistivity of the welds. The microstructures reveal the information of grain structure and bonding. The width of diffusion layer significantly reduced with low dwell times. For a plunge depth of 1 mm, the maximum tensile strength (294 MPa) is achieved during the higher rotational speed (1400 rpm). For the same plunge depth, lower tensile strength values are exhibited by the joint produced using the lower rotational speed (800 rpm). Hardness of the weld region recorded 70 HV which is less than Cu (115 HV) and greater than Al (40 HV). FSSW joints (0.30 to 0.34 μΩ) offered higher range of electrical resistivity than that of base metal (0.02 μΩ). The results highlighted in this paper might be helpful for both academic researchers and industrialists.

Development of Laser-Arc Hybrid Process for Dissimilar Metal Joining of Galvanized Steel to Aluminum Alloy

Development of Laser-Arc Hybrid Process for Dissimilar Metal Joining of Galvanized Steel to Aluminum Alloy

Expanding-welding: A hybrid deformation and welding process for joining dissimilar metals

To achieve ultra-strong joint performance and high processing efficiency of joining dissimilar metals, a novel hybrid process, Expanding-Welding method (EW), was proposed. EW effectively combined metallurgical bonding and mechanical expanding effects in a single process. To demonstrate its effectiveness, EW was applied to join aluminum tube to steel tube-sheet hybrid structure. Molecular dynamics analysis showed that the Al/Fe diffusion coefficient was increased by 2 orders of magnitude under the compression and shear condition. Severe plastic deformation introduced by the welding tool induced rapid atom diffusion behavior, and the thickness of the diffusion layer reached 9.5 ± 0.4 µm. The maximum joint pull-out strength was 176.5 ± 13.7 MPa, reaching 73.5% of that of base Al alloys. The success of this hybrid deformation-welding process can increase energy efficiency in many industrial sectors, such as constructing reliable tube-to-tube-sheet structures with dissimilar metals for heat exchangers in the field of petroleum and chemical industries.