Formation Of Brittle Intermetallic Compounds Research Articles

Improving Mechanical Properties of Dissimilar Material Friction Welds

Friction welding of stainless steel to titanium with aluminum insert metal was investigated to improve the mechanical properties of the joints. Two different methods were used to insert the aluminum as a barrier between to substrates. The process parameters were found to be different for these two methods to obtain the sound welds. The friction welds between stainless steel and titanium with aluminum insert prevented the formation of brittle intermetallic compounds in the weld interface. A new intermetallic compounds such as AlTi and Al3Ti were formed between titanium and aluminum insert metal interface which are more ductile than the FeTi and CrTi intermetallic compounds. The joints characterized that the aluminum insert metal improved the metallurgical reaction at the weld interfaces thus indicates the results of decrease in microhardness of the intermetallic compounds which have major influence on the strength of the joints. The tensile strength of the aluminum insert welds was higher than the direct joints between the stainless steel and titanium. Higher tensile properties were attained at higher upset pressure condition due to the effect of higher force upon the welded materials and the remnant narrower thickness of insert metal.

Challenges and advances in laser welding of dissimilar light alloys: Al/Mg, Al/Ti, and Mg/Ti alloys

With the growing demand for vehicle weight reduction and the increased application of multimaterial design, it is imperative to address the challenges of welding dissimilar light alloys. This paper presents a review on laser welding of Al/Mg, Al/Ti, and Mg/Ti alloys, with focus on the techniques used to suppress the formation of brittle intermetallic compounds (IMCs) and improve joining mechanism. For Al/Mg joints, studies have shown that the use of structural adhesives, the use of interlayers such as Ce, Ni, Ti, and Fe foils and Zn-Al filler metals, and hybrid adhesive-interlayers could suppress the formation of brittle IMCs and improve joint strength. The formation of brittle IMCs during laser welding of Al/Ti alloys could be minimized by offsetting the laser beam at an appropriate distance towards either the Al or Ti alloy, the use of split-beam laser with appropriate joint design, the use of high welding speed, improving the laser energy distribution, and the use of V-groove with Al-Si filler metals. For Mg/Ti alloys, offsetting the laser beam at an appropriate distance towards the Mg alloy, the use of AZ series Mg alloy-based filler wires, and coating the Ti alloy with Ni were found to facilitate the joint formation and improve the joint strength.

Joining of Aluminium Alloy and Steel by Laser Assisted Reactive Wetting

Compounds of dissimilar materials, like aluminium and steel offer an interesting opportunity for the automotive industry to reduce the weight of a car body. Thermal joining of aluminium and steel leads to the formation of brittle intermetallic compounds, which negatively affects the properties of the welded joint. Amongst others, growth of such intermetallic compounds depends on maximum temperature and on the time at certain temperatures. Laser welding with its narrow well seam and its fast heating and cooling cycles provides an excellent opportunity to obtain an ultrathin diffusion zone. Joining of sheet metal DC01 with aluminium alloy AW6016 has been chosen for research. The performed experimental studies showed that by a variation of the beam power and scanning speed it is possible to obtain an ultrathin diffusion zone with narrow intermetallic interlayers. With the aim of supporting further investigation of laser welding of the respective and other dissimilar pairings a multi-physical simulation model has been developed.

Low temperature heat treatments of AA5754-Ti6Al4V dissimilar laser welds: Microstructure evolution and mechanical properties

This paper presents the effects of the post welding heat treatments (PWHT) performed at 350 °C and 450 °C on the microstructure evolution and mechanical properties of AA5754 and Ti6Al4V dissimilar laser welds. The microstructure and tensile properties of the welds before and after low temperature treatment were analyzed.The off-set welding technique was applied to limit the formation of brittle intermetallic compounds during the welding process. The laser beam was directed onto the titanium side at a small distance from the aluminum edge. The keyhole formed and the full penetration was reached in the titanium side of the weld. Thereafter, the aluminum side melted as the heat that formed the keyhole transferred from the titanium fused zone. Two different energy lines (32 J/mm and 76 J/mm) were used. In this manner, a fused and a heat affected zones was revealed on both sides of the weld. Several intermetallic compounds formed in the intermetallic layer between the two metals. The thickness and the composition of the intermetallic layer depended on the welding parameters and the post welding heat treatment.The hardness and tensile properties of the welds before and after the post welding heat treatment were measured and analyzed.

The Effectiveness of Al-Si Coatings for Preventing Interfacial Reaction in Al-Mg Dissimilar Metal Welding

The dissimilar welding of aluminum to magnesium is challenging because of the rapid formation of brittle intermetallic compounds (IMC) at the weld interface. An Al-Si coating interlayer was selected to address this problem, based on thermodynamic calculations which predicted that silicon would change the reaction path to avoid formation of the normally observed binary Al-Mg IMC phases (β-Al3Mg2 and γ-Al12Mg17). Long-term static heat treatments confirmed that a Si-rich coating will preferentially produce the Mg2Si phase in competition with the less stable, β-Al3Mg2 and γ-Al12Mg17 binary IMC phases, and this reduced the overall reaction layer thickness. However, when an Al-Si clad sheet was tested in a real welding scenario, using the Refill™ friction stir spot welding (FSSW) technique, Mg2Si was only produced in very small amounts owing to the much shorter reaction time. Surprisingly, the coating still led to a significant reduction in the IMC reaction layer thickness and the welds exhibited enhanced mechanical performance, with improved strength and fracture energy. This beneficial behavior has been attributed to the softer coating material both reducing the welding temperature and giving rise to the incorporation of Si particles into the reaction layer, which toughened the brittle interfacial IMC phases during crack propagation.

Rational design of composite interlayer for diffusion bonding of tungsten–steel joints

Large residual stresses and brittle intermetallic compounds are two detrimental factors in the mechanical reliability of tungsten–steel joints. In this work, we conduct a rational design of interlayer structure to tackle these two pitfalls by combining finite element model (FEM) and Hume–Rothery rules. The FEM results show that the selection of interlayer materials for tungsten–steel joining depends not only on thermal expansion mismatch, but also on the plastic deformation of interlayer. In practice, it is better to relax the residual stress by a soft interlayer with high ductility than to transfer the stress from W by a hard interlayer with a low coefficient of thermal expansion. However, the Hume–Rothery rules indicate adding a single interlayer cannot prevent the formation of brittle intermetallic compounds. A composite interlayer design is then proposed in this study to minimize the possibility of intermetallic compounds formation in the meantime reduce the residual stress. Using V/Cu and V/Ni as typical examples, we demonstrate that composite interlayer can greatly improve joint performance because of the lower residual stresses and less detrimental intermetallic compounds.

Mechanical and microstructure analysis of AA6061 and Ti6Al4V fiber laser butt weld

Dissimilar metal welding involves the joining of two or more different pure metals or alloys, usually by melting and mixing and often with the addition of filler metal. There are several types of dissimilar metal welds including stainless steel, either as base metal or as filler metals. Dissimilar metal joints have distinctive features because of differences in the chemical composition of base metal and filler material. Their alloying elements will diffuse intensely during welding. The structures near the fusion line are very complex. Despite of great potentiality in aircraft and automotive industries, dissimilar joining of hybrid Al-Ti structures is often challenging because of the unavoidable formation of brittle intermetallic compounds, mixing of molten phases, and significant differences in material properties. In this work, dissimilar 2mm thickness AA6000 and Ti6Al4V butt joints were produced by shifting an Yb fiber laser beam on the upper surface of the Ti sheet. Neither filler wire nor groove preparation was adopted. Different working conditions and seam shapes were assessed. The welds were characterized in terms of metallurgical and mechanical behaviors.

Effects of Laser Offset and Hybrid Welding on Microstructure and IMC in Fe–Al Dissimilar Welding

Welding between Fe and Al alloys is difficult because of a significant difference in thermal properties and poor mutual solid-state solubility. This affects the weld microstructure and causes the formation of brittle intermetallic compounds (IMCs). The present study aims to explore the weld microstructure and those compounds over two different technologies: the laser offset welding and the hybrid laser-MIG (Metal inert gas) welding. The former consists of focusing the laser beam on the top surface of one of the two plates at a certain distance (offset) from the interfaces. Such a method minimizes the interaction between elevated temperature liquid phases. The latter combines the laser with a MIG/MAG arc, which helps in bridging the gap and stabilizing the weld pool. AISI 316 stainless steel and AA5754 aluminum alloy were welded together in butt configuration. The microstructure was characterized and the microhardness was measured. The energy dispersive spectroscopy/X-ray Diffraction (EDS/XRD) analysis revealed the composition of the intermetallic compounds. Laser offset welding significantly reduced the content of cracks and promoted a narrower intermetallic layer.

Microstructural characterisation of rotary friction welded AA6082 and Ti-6Al-4V dissimilar joints

The aim of this work was to investigate the weld interface and microstructure of a rotary friction welded (RFW) Ti-6Al-4V to AA6082 joint for the purpose of future spacecraft applications. A recent initiative by the European Space Agency (contract No. 4000111471/14/NL/PA) towards a more sustainable materials and processes selection has given the development of advanced joining techniques significant momentum. As part of this strategic development, it was proposed to produce propellant and pressurant tanks with aluminum alloys, joined to the Ti-6Al-4V tubing and pipework surrounding the tank with advanced joining methods. Consequently, Omnidea-RTG and IWS were tasked to develop the joining of dissimilar, tube and rod shaped materials via rotary friction welding, a solid-state welding technique. Thorough parameter optimisation of the welding process has resulted in consistent and reliable welds with excellent mechanical properties. Nonetheless, due to the complex kinetics of the RFW process, the potential formation of brittle intermetallic compounds at the weld interface is still a possibility. Therefore, the microstructure of rotary friction welded AA6082 and Ti-6Al-4V joints was investigated. Emphasis was placed on the detailed inspection of the weld interface and the surrounding base alloys, as well as the compositional evolution throughout the interface region.

Simulation model of Al-Ti dissimilar laser welding-brazing and its experimental verification

Formation of dissimilar weld joints of light metals and alloys including Al-Ti joints is interesting mainly due to demands on the weight reduction and corrosion resistance of components and structures in automotive, aircraft, aeronautic and other industries. Joining of Al-Ti alloys represents quite difficult problem. Generally, the fusion welding of these materials can lead to the development of different metastable phases and formation of brittle intermetallic compounds. The paper deals with numerical simulation of the laser welding-brazing process of titanium Grade 2 and EN AW 5083 aluminum alloy sheets using the 5087 aluminum filler wire. Simulation model for welding-brazing of testing samples with the dimensions of 50 × 100 × 2 mm was developed in order to perform numerical experiments applying variable welding parameters and to design proper combination of these parameters for formation of sound Al-Ti welded-brazed joints. Thermal properties of welded materials in the dependence on temperature were computed using JMatPro software. The conical model of the heat source was exploited for description of the heat input to the weld due to the moving laser beam source. The sample cooling by convection and radiation to the surrounding air and shielding argon gas was taken into account. Developed simulation model was verified by comparison of obtained results of numerical simulation with the temperatures measured during real experiments of laser welding-brazing by the TruDisk 4002 disk laser.

Dissimilar metal joining and structural repair of ZE41A-T5 cast magnesium by the cold spray (CS) process

ABSTRACTThe ability to join aluminum to magnesium is important for many industries but is a challenge due to the formation of brittle intermetallic compounds (IMCs). This article presents a practical method to join and provide structural repair of cast ZE41A-T5 cast magnesium (Mg) by the cold spray (CS) process using 6061 Aluminum (Al). In this study, the CS process was used to deposit 6061 Al onto ZE41A-T5 Mg substrates, which were subjected to materials testing and characterization. Shear, hardness, and tensile testing were conducted to determine bond integrity at the dissimilar metal joint. Electron and optical microscopy were performed to analyze the interface and microstructure. A review of dissimilar metal joining techniques is provided for comparative purposes, and the unique bonding mechanisms of cold spray are discussed because of its relevance to the results obtained. Results showed that the cold spray process limited the formation of Mg2Al3 and Mg17Al12 intermetallic compounds and the bond strength of the dissimilar metal joints created by the cold spray process, had an ultimate tensile strength, hardness, and shear strength comparable to the weakest material being joined (Mg). This study serves to demonstrate the potential of the cold spray process to create high strength dissimilar joints and provide structural repair between Mg and Al.

Liquid Phase Diffusion Bonding of AC2C/ADC12 Aluminum Casting Alloy by Using Metal Salt Coated Zn Sheet

Currently, the common way of bonding aluminum together is brazing. However, brazing creates problem when the high brazing temperature causes the formation of brittle intermetallic compound in between the joints prompting the need to circumvent this difficulty by considering transient liquid phase diffusion bonding method as a possible alternative. Being considered as a possible alternative solution, transient liquid phase diffusion bonding is not without problems that need to be overcome. One of these problems is the presence of oxide film on the insert material surface (Zn) necessitating the need to remove or destroy the oxide film without using high temperature and high load. Hence, in this study, the aim is to treat the bonding surface with formic acid for the removal of oxide film and substitution to a metal salt to determine the effectiveness of such treatment by performing tensile test and observation on the fractured surface of samples. From this study, it is found out that the tensile strength of the joint increased with the rise in bonding temperature with or without metal salt generation processing. However, it is understood that with metal salt generation processing, high strength joint can be obtained with lower bonding temperature compared with unmodified joints. It is hypothesized that this is because metallic zinc is generated as a result of surface modification and thermal decomposition of formate in the bond interface at low bonding temperatures.

Magnesium and Aluminium alloys Dissimilar Joining by Friction Stir Welding

Multi-material lightweight structures are gaining a great deal of attention in several industries, in particular where a trade-off between reduced weight, improved performances, and cost compression is required. Magnesium alloys, such as the zinc-rare earth elements ZE41A alloy, fulfill the first two requirements; however, they are susceptible to corrosion and relatively expensive. Lightweight structures hybridization, for instance combining Magnesium alloys and Aluminium alloys, is currently under consideration as a potential solution to this problem. Nevertheless, dissimilar joining of Magnesium and Aluminium alloys is challenging due to the significant differences in physical properties, as well as to the precipitation of brittle intermetallic compounds, such as Al12Mg17 and Al3Mg2. In this study, the dissimilar joining of Magnesium and Aluminium alloys by friction stir welding process is discussed. In particular, 4mm thick plates of ZE41A Mg alloy and AA2024-T3 Al alloy were welded in the butt joint configuration. The feasibility of the process was assessed by means of microstructure and mechanical analysis. The formation of brittle intermetallic compounds was investigated as well.

Intermetallic compounds in friction stirred lap joints between AA5754/galvanised ultra-high strength steel

This paper presents results of joining of AA5754 and DP800 based on the friction stir welding process. Joints were produced by the tool made of H13 tool steel which was allowed to penetrate through the aluminium sheet until reaching the surface of steel sheet without penetrating into it. This approach is an economic and robust way to operate the dissimilar welding process without excessive tool cost. Bonding was achieved by interfacial diffusion reactions between aluminium and iron with a formation of intermetallic compounds. The formation of brittle intermetallic compounds at the interface between the materials was studied. Three intermetallic phases were found at the interface including Al13Fe4, Al5Fe2 and Fe3Zn10. A range of process parameters was identified with a thickness of the intermetallic layers around 2 µm. Shear fracture failure mode was observed under overlap loading. The mechanisms of formation of the joints and factors controlling the strength were discussed.

Effect of bonding pressure on microstructure and mechanical properties of Ti-6Al-4V diffusion-bonded joint

In this study, solid-state diffusion bonding of Ti-6Al-4V alloy using a pure copper interlayer was conducted, and the effect of bonding pressure (0.5 to 4 MPa) on microstructure and mechanical properties was investigated. The joint zones were analyzed by optical microscope (OM) and scanning electron microscope (SEM), and microhardness and shear strength tests were also employed to evaluate mechanical behaviors of the joints. The results showed that diffusion of Cu into the Ti alloy led to the formation and the stability of β-Ti as a strengthening phase in the joint zone. Moreover, the increase in bonding pressure made the joint width be decreased to the minimum value. The maximum shear strength of 571 MPa was achieved for the bond made with 4 MPa bonding pressure, whereas with a decrease in pressure, the shear strength fell to 358 MPa that could be attributed to the increase in the joint width and the formation of brittle intermetallic compounds at the interface.

A review on resistance spot welding of aluminum alloys

This paper presents a review on the resistance spot welding (RSW) of Al/Al alloys, Al alloys/steel, Al/Mg alloys, and Al/Ti alloys, with focus on structure, properties, and performance relationships. It also includes weld bonding, effect of welding parameters on joint quality, main metallurgical defects in Al spot welds, and electrode degradation. The high contact resistance, induced by the presence of oxide layer on the surface of Al alloys, and the need for application of high welding current during RSW of Al alloys result in rapid electrode tip wear and inconsistency in weld quality. Studies have shown that cleaning the oxide layer, sliding of a few microns between sheets, enhancing the electrode force, and the application of a low-current pre-heating can significantly reduce the contact resistance and improve joint quality. For Al/steel dissimilar RSW, the technique of resistance element welding, the use of optimized electrode morphology, the technique of RSW with cover plates, and the use of interlayers such as Al-Mg, AlSi12, and AlCu28 alloys were found to suppress the formation of brittle intermetallic compounds (IMC) and improve the joint quality. The employment of pure Ni foil, Au-coated Ni foil, Sn-coated steel, and Zn-coated steel interlayers was also found to restrict the formation of brittle IMCs during RSW of Al/Mg alloys. Furthermore, the techniques of RSW with cover plates and RSW under the influence of electromagnetic stirring effect were found to improve the weldability of Al/Ti dissimilar alloys.

FeCrAl and Zr alloys joined using hot isostatic pressing for fusion energy applications

FeCrAl and Zr alloys were joined by a hot isostatic pressing (HIP) method for fusion energy applications. The optimum conditions for the joining process were studied. The HIP temperatures were varied from 700 to 1050°C. The mechanical properties of the HIPed samples were evaluated by four-point bending and tensile tests. The FeCrAl and Zr alloys HIPed at 700°C showed higher joint strength than the other samples. The joint strength decreased with an increase in the HIP temperature from 700 to 950°C and significantly dropped at 1050°C. Transmission electron microscopy, scanning electron microscopy, and optical microscopy were used to characterize the joints and interface region of the HIPed samples. The joints appeared to be tightly bonded and no intermetallic compounds or gaps were observed at the interface for HIP temperatures up to 950°C. A diffusion layer formed at the interface and its thickness increased with the HIP temperature. HIP at 1050°C, on the other hand, resulted in significant inter-diffusion and formation of brittle inter-metallic compounds at the interface.

A review on resistance spot welding of magnesium alloys

This paper presents a review on resistance spot welding of magnesium alloys, with emphasis on the relationship between microstructure, properties, and performance, under quasi-static and dynamic loading conditions. It also compares the resistance spot welding of magnesium-to-aluminum alloys and the various techniques used to suppress the formation of brittle intermetallic compounds. Resistance spot welding of magnesium-to-steel, weld bonding, the effects of process parameters on joint quality, and the main metallurgical defects in resistance spot welding of magnesium alloys are also deliberated. Studies have shown that the pre-existence of coarse second phase particles in the base metal, the addition of particles, such as titanium powder, and welding under the influence of electromagnetic stirring effect can promote columnar-to-equiaxed transition, microstructure refinement, and improvement in mechanical properties of magnesium alloys resistance spot welds. For magnesium-to-aluminum alloys spot welds, the use of interlayers, such as pure nickel, gold-coated nickel foil, and zinc-coated steel, was found to suppress the formation of brittle intermetallic compounds and thus significantly improve the joint strength.

Analysis and Characterization of the Role of Ni Interlayer in the Friction Welding of Titanium and 304 Austenitic Stainless Steel

Joining of commercially pure Ti to 304 stainless steel by fusion welding processes possesses problems due to the formation of brittle intermetallic compounds in the weld metal, which degrade the mechanical properties of the joints. Solid-state welding processes are contemplated to overcome these problems. However, intermetallic compounds are likely to form even in Ti-SS joints produced with solid-state welding processes such as friction welding process. Therefore, interlayers are employed to prevent the direct contact between two base metals and thereby mainly to suppress the formation of brittle Ti-Fe intermetallic compounds. In the present study, friction-welded joints between commercially pure titanium and 304 stainless steel were obtained using a thin nickel interlayer. Then, the joints were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, and X-ray diffractometry. The mechanical properties of the joints were evaluated by microhardness survey and tensile tests. Although the results showed that the tensile strength of the joints is even lower than titanium base metal, it is higher than that of the joints which were produced without nickel interlayer. The highest hardness value was observed at the interface between titanium and nickel interlayers indicating the formation of Ni-Ti intermetallic compounds. Formation these compounds was validated by XRD patterns. Moreover, in tensile tests, fracture of the joints occurred along this interface which is related to its brittle nature.

Modeling and experimental analysis of fiber laser offset welding of Al-Ti butt joints

In spite of great potentiality in aircraft and automotive industries, dissimilar joining of hybrid Al-Ti structures is often challenging because of the unavoidable formation of brittle intermetallic compounds, mixing of molten phases, and large differences in material properties. In this work, dissimilar 2 mm thickness AA5754 and Ti6Al4V butt joints were produced by shifting an Yb fiber laser source on the upper surface of the Ti sheet. Neither filler wire nor groove preparation was adopted. Different working conditions and seam shapes were assessed. Results, characterized in terms of microstructure, micro-hardness, and tensile behavior, showed good characteristics and margins for improvement. The finite element analysis supported the investigation and provided temperature distribution and thermal cycle in the workpiece. The calculation was carried out by ANSYS parametric design language (APDL). Temperatures and seam cross section were detected for validating the model. Numerical output approached experimental results with good accuracy.