Formation Of Brittle Intermetallic Compounds Research Articles

Development of Hot-Wire Laser Additive Manufacturing for Dissimilar Materials of Stainless Steel/Aluminum Alloys

The formation of brittle intermetallic compounds (IMCs) at the interface between dissimilar materials causes considerable problems. In this study, a multi-material additive manufacturing technique that employs a diode laser and the hot-wire method was developed for stainless steel/aluminum alloys. An Al-Mg aluminum alloy filler wire (JIS 5183-WY) was fed on an austenitic stainless-steel plate (JIS SUS304) while varying the laser power and process speed and using paste-type flux and flux-cored wire. The effects of laser power and process speed on phenomena during manufacturing and IMC formation were investigated. Finally, the wall-type multilayer specimens were fabricated under optimized conditions. The suppression of IMC formation to a thickness of less than 2 μm was achieved in the specimens, along with a high interfacial strength of over 120 MPa on average.

Direct spot joining of thin gauge aluminum alloy to stainless steel and joint performance in a corrosion environment

Direct joining of aluminum alloy and steel sheets offers a great potential for achieving effective structural lightweighting for transportation systems. The major challenge is how to avoid the formation of brittle intermetallic compounds (IMCs), which can be detrimental to joint load capacity and corrosion resistance. This paper presents a friction-based direct solid-state joining method for welding thin aluminum alloy (AA6061-T6) to stainless steel (316). Using a flat head friction heating tool, high quality interfacial bonding was achieved under a spot time of 20s and 1000 rpm without detrimental IMCs. The effects of an automotive-relevant corrosion environment condition on joint strengths were then examined through mechanical testing. The test results show that aluminum and stainless-steel spot joints produced by the proposed method exhibit no corrosion-induced damage or cracking nor any noticeable reduction in strengths, resulting in dominantly ductile failure mode.

Metallurgical characteristics of aluminum-steel joints manufactured by rotary friction welding: A review and statistical analysis

Rotary friction welding (RFW) is a solid-state joining process that can be used to join different alloy systems such as aluminum-steel alloys. Rotary friction welding has become increasingly appealing for various industries due to the sustainable advantages that it offers, including overall cost reduction, weight minimization, and unique properties. However, the formation of brittle intermetallic compounds (IMCs) at the interface can be a challenge in the welding process of aluminum-steel alloys. This paper reviews the metallurgical characteristics of aluminum-steel alloy joints manufactured by rotary friction welding. The different types of intermetallic compounds that can form at the interface, as well as the factors that affect their formation, are discussed. The effects of rotary friction welding parameters on the microstructure and mechanical properties of the joints are also presented. Specifically, minimizing interfacial reaction layers via post-weld heat treatment and controlling the heat input during the process is crucial to suppressing the formation of intermetallic compounds. This study employed artificial intelligence modeling, specifically the artificial neural network - multilayer perceptron, to investigate the effect of various parameters on the ultimate properties of the parts welded together. Overall, this paper provides an excellent resource for industries looking to embrace rotary friction welding to tackle the challenge of dissimilar Al-steel joining.

Effect of Ag interlayer on the microstructural properties and nanocreep behavior of Ti6Al4V/AA7075 dissimilar laser weldments

Creep failure poses a potential risk in dissimilar welded joints between aluminum and titanium alloys, potentially compromising the joint's integrity. This study utilizes laser beam welding (LBW) to achieve dissimilar joining of AA7075 and Ti6Al4V by incorporating an Ag interlayer. The role of Ag interlayer for dissimilar joining of AA7075 and Ti6Al4V alloys and its impact on the microstructure and nanocreep behavior of joints is examined. The findings showed that the use of Ag decreased the interaction of Ti/Al considerably with each other which led to a reduction in the formation of brittle intermetallic compounds. The nanohardness and atomic force microscopy (AFM) results indicated that the Ti6Al4V HAZ exhibited the highest hardness and least plastic deformation, owing to the formation of α′ martensite. The nanoindentation creep analysis revealed the highest stress exponent value in Ti6Al4V HAZ, pointing to a dislocation climb creep mechanism. Additionally, the results also suggested that the observed creep mechanism might be attributed to both diffusional creep and dislocation climb for other zones.

A Novel Strategy for Realizing Reliable Welding of Aluminum-Steel

This study proposed a novel welding strategy called active-expulsion-assisted resistance spot welding (RSW), which was used to address the limitations of RSW of aluminum to steel. The method primarily comprised an intentionally set expulsion stage and a locking stage. In the expulsion stage, a short-duration expulsion pulse with a relatively large welding current was applied to melt the aluminum and induce liquid aluminum expulsion. Then, in the locking stage, a welding current pulse was used to join the locking sheet and the steel workpiece. A combination of quenched and partitioned 1180 steel and AA6016 aluminum alloy with and without adhesive was used for welding. Experimental results showed that the expulsion pulse efficiently removed the aluminum alloy in the weld, creating the conditions for fundamentally avoiding the formation of brittle intermetallic compounds in the nugget during the subsequent welding stage. After the welding pulse, a strong joint was generated between the locking sheet and the steel, thus realizing a firm connection for the combination of welding and riveting between an aluminum alloy and steel substrate.

Development of directed energy deposition strategy for a mechanically interlocked pure Ti and Al alloy component with cross-shaped internal pure Ti lattice

Directed energy deposition (DED) using multi-metal materials typically employs a metallurgical bonding approach. The components using titanium (Ti) and aluminum (Al) alloys have attracted significant interest in aerospace and automotive industries due to their ability to decrease fuel consumption through lightweight construction. However, DED using Ti and Al alloys that are difficult to fusion-bond is plagued by the formation of brittle intermetallic compounds. In particular, the deposition of a Ti alloy layer on that of Al alloy decreases the mechanical property of the entire component. This study developed a DED strategy using wire and arc discharge for the mechanical interlocking of pure Ti ERTi-2 and Al alloy ER5356. First, the effects of heat input, fabrication paths, and arc locations on the interface and composition of the adjacent beads were clarified. A fabrication strategy was developed to achieve the desired fusion state and avoid collision between welding torch-fabricated component. A mechanical interlocked component with an internal ERTi-2 cross-shaped lattice and planar ERTi-2 surface layers was successfully fabricated. In addition, these results demonstrate that the developed fabrication strategy can be applied to the other metal combinations that are difficult to fusion-bond. Subsequently, X-ray computed tomography clarified that the internal ERTi-2 lattice was fabricated in the target geometry. Tensile tests were carried out using the mechanical interlocked components with an internal cross-shaped unit lattice. The yield and ultimate tensile strength were 45.1 ± 3.4 MPa and 55.5 ± 4.6 MPa, respectively. These values and the fracture positions were in good agreement with the predictions from the mechanical properties of the used materials and the lattice geometry. Hence, this study underscores the potential of mechanical interlocking to improve the mechanical properties of the multi-metal components that pose challenges for fusion-bonding.

Crack-Free Copper Alloy Coating on Aluminum Alloy Fabricated by Laser Cladding

Crack-free Cu alloy coating has been fabricated on Al alloy substrate with the existence of a Ag buffer layer. The Cu alloy coating had 12 at.% Al and 45 at.% Ag, which contributed to the formation of Cu solid solution and the eutectic phase (transformation temperature 780 °C). The eutectic phase was characterized as finer Cu solid solution and finer Ag solid solution. The Ag buffer layer had the main contents of Ag2Al and Ag solid solution, and it not only hindered the formation of brittle intermetallic compounds (IMCs)but also reduced the thermal stress as its intermediate coefficient of thermal expansion (CTE). Furthermore, the plastic deformation of Ag solid solution in the Ag buffer layer and Cu solid solution in Cu alloy coating also relieved the thermal stress which was generated during the cladding process. All these three aspects inhibited crack generation. And the hardness of the Cu alloy coating increased to approximately 275 HV due to the strengthening effect of Al solid solution, grain boundary within the finer eutectic phase, and nano twin in the Cu solid solution of the eutectic phase.

Dissimilar laser welding of NiTi shape memory alloy to NiCr alloy

NiTi shape memory alloy (SMA) offers a wide range of industrial applications due to its shape memory effect and superelastic properties. In this study, a dissimilar joint between NiTi SMA and Ni–20Cr alloy was fabricated, and its microstructural and mechanical properties were analyzed. As a result of the formation of brittle intermetallic compounds (IMC), the tensile characteristics were reduced, and the hardness increased dramatically. Also, the effect of various laser pulse widths on bonding characteristics was examined, and as the pulse width increased, coarser IMCs were formed in the FZ. By performing post-weld heat treatment (PWHT) on the welded samples, the microstructure and mechanical properties of the FZ changed, and the NiTi intermetallic phase was produced. The results revealed that most IMCs generated had the same chemical composition ratio as Ni3Ti and Cr2Ti IMCs. In addition, after PWHT, the plateau region in the stress-strain curves was formed, while in the welded samples without PWHT, the joints failed at low stress and strain before forming the plateau region.

Analysis of laser welding on dissimilar materials with the influence of adding interlayer

The laser welding of dissimilar materials poses several challenges in practical applications, such as molten pool instability, the formation of intermetallic compounds (IMCs), and cracking caused by differential thermal stresses. In this study, we investigated the impact of incorporating a nickel (Ni) foil as an intermediate layer on lap joints of dissimilar materials (SS304 and Al6061) welded using the continuous laser welding (CLW) technique. The thermomechanical simulation accurately predicted the width and depth of SS304–Ni–Al6061 joints, with deviations of merely 3.92% and 19.04% from experimental results, respectively. Residual stress analysis revealed that the addition of a nickel foil reduced residual stress in the heat-affected zone (HAZ) and improved joint fatigue life. Furthermore, the incorporation of 0.1 and 0.2 mm Ni foils enhanced joint strength and effectively suppressed the formation of brittle intermetallic compounds, resulting in a remarkable maximum lap shear force of up to 1026 N. The simulation results for the shear load-displacement curve displayed excellent agreement with experimental data, with a deviation of only 6%. Notably, joints with the Ni foil demonstrated a greater ability to prevent crack formation caused by thermal expansion mismatch compared to joints without the Ni foil. The Ni interlayer served as a diffusion barrier and stress buffer, promoting a more uniform microstructure and reducing the likelihood of crack formation in bonded materials. Overall, this study comprehensively investigates the impact of incorporating a nickel interlayer on laser-welded lap joints of dissimilar materials. The findings offer valuable insights for practical applications, enabling improved joint strength, reliability, and crack resistance in laser welding dissimilar materials.

Solid-State Welding of Aluminum to Magnesium Alloys: A Review

With the continuous improvement of lightweight requirements, the preparation of Mg/Al composite structures by welding is in urgent demand and has broad prospective applications in the industrial field. However, it is easy to form a large number of brittle intermetallic compounds when welding Mg/Al dissimilar alloys, and it is difficult to obtain high-quality welded joints. The solid-state welding method has the characteristics of low energy input and high efficiency, which can inhibit the formation of brittle intermetallic compounds and help to solve the problem of the poor strength of welded joints using Mg/Al dissimilar alloys in engineering applications. Based on the literature of ultrasonic welding, friction welding, diffusion welding, explosive welding, magnetic pulse welding, and resistance spot welding of Al/Mg in recent years, this paper summarized and prospected the research status of solid-state welding using Mg/Al dissimilar alloys from three aspects: the optimization of welding parameters, the addition of interlayers, and hybrid welding process.

Microstructural and mechanical characterisation of reinforced aluminium foam sandwich panels made by one-step squeeze casting method

ABSTRACT In just one step, a squeeze casting process was applied to produce aluminium foam sandwich panels. NaCl particles with mean sizes of 4.75 and 6.35 mm were used as space holders in different proportions. In-situ face sheet manufacturing was conducted through previously placed steel meshes in the mould. The effect of NaCl particle sizes and the proportion of each size on porosity, microstructure, and mechanical properties were investigated. Results showed a decline from 59.8% to 43.8% in the porosity amount of samples with increasing the proportion of larger NaCl particles. Accordingly, an increase in compression yield stress (from 3.2 to 6.1 kgf/mm2) and the absorbed energy were observed. Also, at the elevated densities of the sandwich panel core, the plateau stress was enhanced. The presence of Cu, Ni, Fe, and Si elements leads to the formation of brittle intermetallic compounds in the microstructure of cell walls.

Compositive role of refractory element Mo in improving strength and ductility of face-centered-cubic complex concentrated alloys

Complex concentrated alloys (CCAs) with a face-centered-cubic (FCC) structure exhibit remarkable mechanical properties, introducing the expansion of compositional space in alloy design for structural materials. The formation of a single solid-solution phase is enabled by configuring various 3d-transition elements, while doping other elements even of a small portion generally leads to the formation of brittle intermetallic compounds. Herein, we demonstrate through a systematic investigation of single FCC (CoNi)100-xMox alloys that a wide range of refractory element Mo can simultaneously improve the strength and ductility while sustaining the solid-solution structure. The addition of Mo with a larger atomic size than those of 3d-transition elements introduces severe lattice distortion in the FCC lattice and causes grain-boundary segregation enriched by Mo atoms. In addition, increasing Mo content effectively reduces the stacking fault energy (SFE). The increased lattice distortion with Mo content enhances the solid-solution strengthening of the alloys. Besides, along with reduced SFE and stabilization of the dislocation emission site by grain-boundary segregation, this elevated solid-solution strengthening increases grain-boundary strengthening, reaching a yield strength of ∼1 GPa. Moreover, the reduction of SFE with increasing Mo results in the transition of dislocation substructures and the refinement of deformation twins, allowing for enhanced strain-hardening capability and thus ∼1.3 GPa tensile strength and ∼50% ductility. Such compositive and synergetic effects of refractory element Mo enable the CCAs with a single FCC solid solution to overcome the strength and ductility trade-off.

Design and mechanical properties of body-centered cubic AlVCr medium-entropy aluminum alloys

The formation of brittle intermetallic compounds and the poor solubility of other metallic elements in Al alloys render the design of high- and medium-entropy Al alloys (HEAls and MEAls, respectively) challenging. Herein, new AlVCr MEAls were developed based on a reverse approach, which involved starting from an equiatomic V–Cr alloy. Al20VCr, Al33VCr, and Al50VCr were synthesized as MEAls using a vacuum induction-based melting process. The microstructural evolution and mechanical properties of the synthesized MEAls were carefully investigated. Body-centered cubic single-phases formed in Al20VCr and Al33VCr MEAls, in keeping with thermodynamic calculation results as well as multiple phase-prediction parameters. While Al33VCr exhibited brittle fracturing owing to chemical ordering, Al20VCr MEAl exhibited a compressive strain and yield strength of ∼9.4% and ∼1.0 GPa, respectively. Thus, the reverse approach, which is based on the use of an Al-free system initially, should aid the development of a new class of lightweight HEAls and MEAls.

Joining of SiC ceramics using high-silicon aluminum alloy fillers assisted by laser cladding

A Si–40Al joining transition layer was prepared via laser cladding, followed by brazing of SiC ceramics using Si–60Al alloy as the joint filler. The microstructure, composition, and flexural strength of the brazed joints were investigated under different brazing temperatures and holding times. The corrosion resistance of the joints was evaluated using a hydrochloric acid immersion test. The laser cladding layer effectively reduced interfacial stress, enhanced interfacial bonding, and suppressed the formation of brittle intermetallic compounds. The main constituents of the brazed joint were Si, Al2O3, and SiC, with newly formed SiC at the interface promoting interfacial bonding. The flexural strength of the brazed joint held at 900 °C for 30 min exceeded 279 ± 13 MPa, equivalent to that of the SiC substrate. Compared to direct brazing of SiC using Si–60Al alloy filler and Si–40Al alloy filler, the strengths were increased by 49% and 94%, respectively. Furthermore, the joints exhibited excellent corrosion resistance, with a flexural strength of 177 ± 11 MPa after 10 h of hydrochloric acid immersion.

Studies on Metallic Glasses in Utsunomiya University

Studies on dissimilar metal welding and mechanical fastening using metallic glasses in Utsunomiya University have been introduced. Metallic glass ribbons placed between the two dissimilar metal plates become supercooled liquid with low viscosity by resistance welding and promote supercooling at the nuggets. As a consequence, the residual stress at the welding boundary and the formation of brittle intermetallic compounds are suppressed, resulting in excellent dissimilar resistance welding with high joint strength and high reproducibility. Mechanical fastening of two metal plates is also demonstrated by resistance heating and viscous flow forming of metallic glass rivets. Producing metallic glass rivets using bulk metallic glasses by a resistance heating is now under examination.

Numerical Simulation of Temperature Fields during Laser Welding-Brazing of Al/Ti Plates.

The formation of dissimilar weld joints, including Al/Ti joints, is an area of research supported by the need for weight reduction and corrosion resistance in automotive, aircraft, aeronautic, and other industries. Depending on the cooling rates and chemical composition, rapid solidification of Al/Ti alloys during laser welding can lead to the development of different metastable phases and the formation of brittle intermetallic compounds (IMCs). The effort to successfully join aluminum to titanium alloys is associated with demands to minimize the thickness of brittle IMC zones by selecting appropriate welding parameters or applying suitable filler materials. The paper is focused on the numerical simulation of the laser welding-brazing of 2.0 mm thick titanium Grade 2 and EN AW5083 aluminum alloy plates using 5087 aluminum filler wire. The developed simulation model was used to study the impact of laser welding-brazing parameters (laser power, welding speed, and laser beam offset) on the transient temperature fields and weld-pool characteristics. The results of numerical simulations were compared with temperatures measured during the laser welding-brazing of Al/Ti plates using a TruDisk 4002 disk laser, and macrostructural and microstructural analyses, and weld tensile strength measurements, were conducted. The ultimate tensile strength (UTS) of welded-brazed joints increases with an increase in the laser beam offset to the Al side and with an increase in welding speed. The highest UTS values at the level of 220 MPa and 245 MPa were measured for joints produced at a laser power of 1.8 kW along with a welding speed of 30 mm·s-1 and a laser beam offset of 300 μm and 460 μm, respectively. When increasing the laser power to 2 kW, the UTS decreased. The results exhibited that the tensile strength of Al/Ti welded-brazed joints was dependent, regardless of the welding parameters, on the amount of melted Ti Grade 2, which, during rapid solidification, determines the thickness and morphology of the IMC layer. A simple formula was proposed to predict the tensile strength of welded-brazed joints using the computed cross-sectional Ti weld metal area.

A study of interfaces in 7075/Zr44Ti11Cu10Ni10Be25(Vit1b)/AZ31B composites

In order to achieve reliable connection between magnesium and aluminum alloys and to prepare composite structures and devices with excellent overall performance, it is critical to avoid the formation of brittle intermetallic compounds. In this regard, we describe hot stacked extrusion forming of 7075/Zr44Ti11Cu10Ni10Be25(Vit1b)/AZ31B in terms of extrusion process parameters and their influence on structure, interfaces, and mechanical properties. The study demonstrated that the composite had almost no defects such as extruded flying edges or bending. The nature of the samples varied considerably and the 450°C-4 mm/min sample showed a more desirable bonding appearance. The samples obtained under different extrusion conditions experienced different degrees of elemental diffusion at the interfaces. It is underscored that using amorphous alloy as the joining medium can effectively improve the strength of 7075/Vit1b/AZ31B composites, with the tensile strength increased by 12.5%. The 7075/Vit1b and AZ31B/Vit1b interfaces were studied systematically and the Al concentration layer was found at the AZ31B/Vit1b interface.

Experimental Study of Steel-Aluminum Joints Made by RSW with Insert Element and Adhesive Bonding.

This work focuses on joining steel to aluminum alloy using a novel method of joining by resistance spot welding with an insert element based on anticorrosive steel in combination with adhesive bonding. The method aims to reduce the formation of brittle intermetallic compounds by using short welding times and a different chemical composition of the insert element. In the experiment, deep-drawing low-carbon steel, HSLA zinc-coated steel and precipitation-hardened aluminum alloy 6082 T6 were used. Two types of adhesives-one based on rubber and the other based on epoxy resin-were used for adhesive bonding, while the surfaces of the materials joined were treated with a unique adhesion-improving agent based on organosilanes. The surface treatment improved the chemical bonding between the substrate and adhesive. It was proved, that the use of an insert element in combination with adhesive bonding is only relevant for those adhesives that have a load capacity just below the yield strength of the substrates. For bonded joints with higher load capacities, plastic deformation of the substrates occurs, which is unacceptable, and thus, the overall contribution of the insert element to the load capacity of the joint becomes negligible. The results also show that the combination of the resistance spot welding of the insert element and adhesive bonding facilitates the joining process of galvanized and nongalvanized steels with aluminum alloys and suppresses the effect of brittle intermetallic phases by minimizing the joining area and welding time. It is possible to use the synergistic effect of insert element welding and adhesive bonding to achieve increased energy absorption of the joint under stress.

Friction Stir Lap Welding of Inconel 625 and a High Strength Steel

The joining of dissimilar hard metals such as high-strength steel and nickel-based alloy is required for shipbuilding and offshore applications to enhance the strength, fracture toughness, and corrosion resistance of the exposed parts. However, the joining of these dissimilar alloys has remained a major challenge due to the limited solubility of Fe and Ni in each other, which commonly results in the formation of brittle intermetallic compounds. We present here a novel investigation on the joining of overlapped nickel-based alloy 625 and marine-grade GL E36 steel plates by friction stir lap welding (FSLW). The interface microstructure and its influence on joint strength are rigorously tested. The main bonding mechanism is found to be the mechanical mixing of Fe and Ni along the interface. The interface thermal cycles are computed by a three-dimensional numerical heat transfer model and their effects on the microstructure are examined. Multiple micro tensile specimens are extracted from the stir zone to examine the through-thickness variation in the stir zone properties. The welded joint is characterized further by evaluating the interface microhardness distribution, lap-shear strength, and surface residual stresses.

Direct energy deposition of Cu–Nb functionally graded layers for dissimilar joining titanium alloys and steels

The heterogeneous compounds of titanium and iron steel are of wide interest in additive manufacturing. To prevent the formation of brittle intermetallic compounds, a layer of Nb and Cu was used. The use of the Nb and Cu interlayer successfully prevents the mixing of Ti and Fe, thus avoiding the formation of FexTiy brittle phases. In the Ti–Nb–(Nb + Cu–10Al) transition interlayer, it was possible to achieve the interlayer without the formation of brittle phases. The static tensile strength of the Grade1/316 L compounds with Nb–(Nb + Cu–10Al) interlayer is 335.5 MPa, the compounds exhibit ductile–brittle fracture.