Intermetallic Layer Research Articles

Minimizing material flow in the dissimilar joining of Al6061 and Ti6Al4V to mitigate the adverse effects of intermetallic compounds

Static shoulder friction stir welding (SSFSW) offers a promising solution for joining Al6061 and Ti6Al4V by addressing material mixing and intermetallic formation encountered in conventional friction stir welding (CFSW). SSFSW effectively suppresses material mixing and Al-Ti interdiffusion, leading to an Al5Ti2 – Al3Ti sequence through an exothermic reaction. Comparative analysis with underwater friction stir welding (UWFSW) highlights SSFSW's effectiveness, showing a significant reduction in intermetallic layer thickness compared to UWFSW. The intermetallic layer thickness of SSFSW is measured at 2.169 µm, while UWFSW exhibits a thickness of 3.731 µm, and CFSW shows the highest at 5.485 µm. The inverse pole figure confirms reduced material flow and intermetallic formation in SSFSW compared to UWFSW and CFSW.

Microstructural Evolution and Material Flow during Friction Stir Welding of 6013 Aluminum Alloy Studied by the Stop-Action Technique

This work is part of a wide-ranging study aiming to enhance the technology of dissimilar friction-stir welding of aluminum and titanium. In the previous study, a new approach was proposed that provided an exceptionally narrow intermetallic layer. However, an essential disadvantage of this technique was the significant material softening in the aluminum part. Hence, the present work was undertaken in order to obtain insight into microstructural processes and material flow in the aluminum part. To this end, the stop-action technique was applied. It was found that the microstructural evolution included several stages. Specifically, the initial material underwent the discontinuous static recrystallization in the heat-affected zone. With the approach of the rotating tool, the recrystallized grains experienced continuous dynamic recrystallization, which resulted in grain refinement. The subsequent transportation of material around the rotating tool provided no significant alterations in microstructure. This “superplastic-like” character of material flow was attributed to a dynamic balance between grain refinement and grain coarsening. It was also found that the stirred material experienced a secondary deformation induced by the rotating tool shoulder far behind the welding tool. The concomitant microstructural changes were most pronounced at the upper weld surface and gave rise to a fine-grained layer.

Nucleation and Location of Kirkendall Voids at the Tin‐Based Solder/Copper Joint: A Review

Void nucleation is a critical issue in wetting because it negatively impacts the solder joint and diminishes its electrical and mechanical properties. Generally, the Kirkendall effect (unbalanced diffusion) and Kirkendall voids (KVs) are developed due to dissimilar diffusivities of species (Cu and Sn) in a diffusion process. However, voids are also nucleated in the supersaturating condition, creating an additional position at or inside the “Kirkendall voids” interface. Various factors (surface modification, reinforcement of fourth elements, substrate type, and impurities) and the environment also support the nucleation of voids. Many researchers have discussed that KVs are nucleated into to intermetallic compounds layers. Reviewing the significant parameters for developing the KV in solid–liquid and solid–solid conditions is essential. Hence, in this review, the potential process of development of the KVs, concepts of thermodynamics, chemical reactions, and growth kinetics are developed. The position and reduction of KVs nucleation are also explained in this paper.

Features of Intermetallic Formation in the Solid Phase on a Steel–Titanium Bimetal Interface under the Conditions of Arc Welding

The object of this study is the formation of intermetallic phases (IMPhs) in the heat-affected zone (HAZ) of joints of steel–titanium bimetal plates produced by arc welding. A titanium layer (2 mm) was welded by the plasma method (PAW), a barrier layer of Cusi3Mn1 bronze was deposited on it by the TIG method, the first steel layer was deposited by CMT, and Puls-MAG was used for filling the groove. Here, heating in the solid phase takes place in the HAZ, which may lead to undesirable formation of brittle IMPhs and further welded joint failure. Mathematical modeling was performed and metallurgical features formed during the processes of heating of the HAZ in bimetal steel–titanium plates were studied to identify the risk of IMPh formation. It was found that at a temperature increase from 900 to 1450 °C, a continuous intermetallic layer formed on the steel–titanium interface, which contained FeTi IMPh, and the width of which increased from 1 to 10 μm. In the temperature range 1300…1430 °C, an intermetallic TiFe2-type phase additionally formed from the titanium side. In the temperature range 1430…1450 °C, the TiFe2 phase was replaced by the TiXFe phase, which formed both from the steel side and from the titanium side. This phase consists of intermetallics (73–75% Ti + 27–25% Fe) and (80–85% Ti + 20–15% Fe), and it is close to the Ti2Fe-type phase. The interlayer of intermetallics, formed at temperatures of 900…1300 °C, has a continuous morphology (HV0.01–650…690). At temperatures rising above 1300 °C, the IMPh interlayer became more ramified (HV0.01–590…610) because of the formation of a larger number of pores and microcracks within it. In the temperature range 900…1450 °C, solid-phase diffusion proceeded in the steel–titanium bimetal near the interface of the two metals. A zone of iron diffusion, 5–10 μm to 40–60 μm in width, formed in titanium. In steel, a zone of titanium diffusion 15–20 μm to 120–150 μm in width formed, starting from 1300 °C and higher. It is recommended to perform industrial welding of steel–titanium bimetal in modes, for which the heat input is equal to 200…400 J/mm. Here, during the period 10–12 s, the heating temperature of the HAZ 1.5–3.5 mm in width is equal to 900–1150 °C. It promotes formation of an intermetallic FeTi-type interlayer of up to 1–2 μm width.

Reverse cladding of 304 stainless steel to LM25 aluminium alloy through die-casting

Stainless steel (SS) coatings/claddings over aluminium alloy (AA) substrates have been practiced through friction surfacing, thermal and cold gas spraying, laser coating, and diffusion bonding. In this work, 304-grade SS is reverse-cladded to an LM25 AA through die-casting using a surface-prepared sheet insert. The clad-substrate interface was characterized micrographically and compositionally through optical and electronic microscopic techniques. Micrographs revealed that reverse cladding was achieved successfully by forming an intermetallic zone (IMZ). The IMZ contains four intermetallic layers (IMLs) of varying thickness with 6.42 ± 2.04 µm near the central region. Electron probe microanalysis showed Fe3(Al, Si), Fe3(Si, Al), Fe(Al, Si), and Fe3Al15Si2 are the associated phases with four IMLs from the SS to AA side, respectively.

Metal deposited nanoparticles as “bridge materials” for lead-free solder nanocomposites

An influence of carbon nanotubes and carbon nanospheres coated by Au–Pd and Pt on the microstructure of solder/copper joints at room temperature and after aging at sub-zero temperature. The carbon nanosized admixtures were mixed with ternary Sn3.0Ag0.5Cu matrix to prepare a composite solder. The microstructure of the solder joints between the nanocomposite solders and a copper substrate was studied by scanning electron microscopy. It was found that minor (0.05 wt. %) admixtures of both the carbon nanospheres and nanotubes increase the shear strength of the solder joints and reduce the growth rate of the intermetallic Cu6Sn5 layer, formed at the interface between solder and copper. This effect may be related to the adsorption of nanoinclusions on the grain surface during the solidification process. Comparative analysis suggests that exposure for 2 months at 253 K does not lead to deterioration of such an important mechanical characteristic of the solder joint as shear strength, indicating the possibility of using these nanocomposite solders in microelectronic equipment even at temperatures below 0 ℃.

Weld formation, microstructure and mechanical properties of magnesium alloy and Al-Si-coated steel dissimilar lap joints fabricated by the CMT weld-brazing process

Magnesium alloy and Al-Si-coated steel dissimilar lap joints were joined using the CMT welding process. The weld formation, microstructure and mechanical properties of Mg/steel CMT weld-brazing joints were investigated. The wetting and spreading behaviour of the molten magnesium alloy filler material on the steel substrate were evidently improved owing to the presence of the Al-Si coating. The Fe-Al intermetallic reaction layer formed at the interface and enhanced metallurgical bonding between the magnesium alloy and steel. The effects of the Al-Si coating and welding heat input on interface layer characteristics were particularly assessed. When the heat input was 178.1 J/mm, the tensile shear strength of the Mg/steel welded joints reached 359.3 N/mm. The fracture modes and failure mechanism for tensile shear specimens were analysed and discussed in detail.

Growth behavior of intermetallic layers at the interface between Cu and eutectic Sn–Bi by grain boundary diffusion with the grain growth at solid-state temperatures

The growth kinetics and rate-controlling processes of intermetallic layers formed in Cu/(Sn-58 wt% Bi) diffusion couples were investigated. Isothermal annealing of diffusion couples was conducted in the temperature range of 363–393 K for various times up to 384 h. In the diffusion couple, an intermetallic layer composed of Cu6Sn5 with irregular scallop shapes and Cu3Sn with relatively uniform thickness forms at the Cu/(Sn–Bi) interface. Isothermal sections of the equilibrium phase diagram in the ternary Bi–Cu–Sn system were calculated at the isothermal annealing temperatures and the peak temperature of the reflow process by a CALPHAD (calculation of phase diagrams) method. The diffusion path passes through the three-phase tie-triangle, including Cu6Sn5 and Cu3Sn. The obtained thicknesses were plotted against the annealing time, and a power function equation was found to describe their relationship. The values of the exponent in the power function were close to 0.25, indicating that the layer growth was predominantly controlled by boundary diffusion with the grain growth. Furthermore, the exponent values were relatively insensitive to the annealing temperature. The relationship between the exponent and the annealing temperature was analyzed, and it was concluded that the grain growth in the intermetallic layer followed a parabolic law. The growth and morphology evolution of the intermetallic compound and Sn–Bi eutectic microstructure at the interface were depicted, shedding light on the widening of the eutectic microstructure. Additionally, the activation enthalpy for the rate-controlling process of intermetallic layer growth at solid-state temperatures was evaluated using a least-squares method, providing insights into the energy barrier for the diffusion or transport of atoms across the interface. This study contributes to a better understanding of intermetallic layer formation and growth in Cu/(eutectic Sn–Bi) diffusion couples, offering valuable information for developing reliable solder joints and high-temperature solders.

Growth process and mechanism of hot-dip galvanised Zn–5Al coating on steel

ABSTRACT In this paper, the growth process and mechanism of hot-dip galvanised Zn–5Al coating on steel at different bath temperatures and immersion times were investigated by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The result shows that the growth of Zn–5Al coating is approximately divided into three stages: initial incubation stage, rapid thickening stage and steady detaching stage. The thickening and outbreak of the intermetallic layer is responsible for the thickening of the coating. When immersed into the Zn–Al bath, an Fe–Al intermetallic layer forms on the interface of liquid and steel and prevents the coating growing at the initial time; with the immersion time increasing, the solid-soluble Zn in the Fe–Al intermetallic layer makes the intermetallic layer unstable, the liquid Zn is discharged outward from the intermetallic layer and many pores and cracks occur, making the coating growth enter the rapid thickening stage. As the liquid phase areas keep expanding, the intermetallic layer will start to detach outward and produce a large amount of dross, the coating with linear growth finally enters the steady detaching stage. Increasing the immersion temperature will accelerate the growing rate of the coating and shorten the initial incubation stage of the coating.

TEM Study of a Layered Composite Structure Produced by Ion-Plasma Treatment of Aluminum Coating on the Ti-6Al-4V Alloy

Using the methods of transmission electron microscopy and energy-dispersive spectroscopy, we study the microstructure and phase composition of the coating and modified intermetallic layers obtained in a Ti-6Al-4V alloy by the deposition of the Al coating and subsequent processing in low-pressure non-self-sustained arc discharge plasma (CIPT—complex ion-plasma treatment). The deposition of the aluminum coating on the Ti-6Al-4V alloy is accompanied by the formation of a layered and a gradient microstructure: nanocrystalline near the “coating/substrate” interface and ultrafine-grained in the outer part of the aluminum coating, with α-stabilized region of ≈5 µm thick in the surface layer in base titanium alloy. After the CIPT, the coating and the surface of the base titanium alloy have a layered morphology: each of the layers possesses different grain structure and composition. In the direction from the outer surface of the specimen to the base material, the following phase sequence has been confirmed by diffraction and elemental analysis: TiAl3 → TiAl3 + nc-(Al(Ti) + α-Ti) → nc-(Al(Ti) + α-Ti) → TiAl3 → TiAl3 + TiAl → TiAl → Ti3Al → α-Ti alloy → (α + β)-Ti alloy. The nanocrystalline aluminum layer, which has been formed during the deposition of the aluminum coating, does not undergo phase transformation and recrystallization under the CIPT. Nanocrystalline structure can favor the interdiffusion of the elements between the coating and base material, and stimulate phase transformation in coarser grains situated under and over it.

Experimental kinetic study of interdiffusion behavior and intermetallic compound Zr(Fe,Cr)2 formation at the Cr/Zry4 interface under elevated temperatures

Interdiffusion behavior at the Cr-Zr interface under elevated temperatures in Cr-coated Zr-based accident tolerant fuel cladding is a key phenomenon for understanding its microstructural stability during the reactor's long-term operation. The interdiffusion behavior of the Cr/Zircaloy-4 (Zry4) diffusion couple and microstructural evolution at the interface were studied under vacuum conditions in the temperature range 973 K to 1323 K. Results show that interdiffusion results in the formation of a Zr(Fe,Cr)2 intermetallic compound layer irrespective of the annealing temperature. Segregation of Fe in the Zr(Fe,Cr)2 interlayer is confirmed, which is enhanced by annealing temperature within the α-Zr phase temperature regime and dropped greatly within the β-Zr temperature regime. The kinetic growth model for Zr(Fe,Cr)2 is found to follow the parabolic law in both α-Zr and β-Zr phase regions, and the diffusion activation energy (Q) of Cr in Zr(Fe,Cr)2 is determined as 7.23×104Jmol−1 for α-Zr phase annealing. Extrapolation of the diffusion coefficients measured within the α-Zr phase predicts a much lower value within the β-Zr phase compared to the experimental result, indicating that the α→β(Zr) phase transformation promotes the growth rate of Zr(Fe,Cr)2 interlayer formation, likely due to the enhancement in both diffusion ability and solubility of Cr in β-Zr relative to α-Zr. The insights obtained in this study will help to improve the understanding of the cladding's microstructure stability and its related degradation behaviors during practical application.

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.

Evaluation of dissimilar 7075 aluminum/AISI 304 stainless steel joints using friction stir welding

Friction stir welding of dissimilar 7075 aluminum/AISI 304 stainless steel joints was done using different tool rotational speed values. The weld was mainly formed in the aluminum part due to the offset value, and stainless steel particles were surrounded with the stirred fine-grained Al matrix. Intermetallic compounds consisting of FeAl3, Fe3Si, FeAl, Fe4Al13 and Fe3Al2Si4 were found in the weld bead. The thickness of the intermetallic compound layers was increased up to 6 µm by increasing the tool rotational speed. Moreover, the stir zone was mainly characterized by a composite-like structure. The weld strength was increased significantly by decreasing the tool’s rotational speed. The maximum strength of joints was about 72% of 7075 aluminum strength. The formation of extensive intermetallic compound layers could be the reason for the reduced joint strength. In specimens with higher tool rotational speeds, fracture occurred within the stir zone.

Wetting kinetics, spreading phenomena and interfacial reaction of Sn-15Bi-xZn solders on Cu substrate at different temperatures

PurposeThis study aims to analyze the wettability of the self-developed Sn–Bi–Zn solder and to conduct a series of analysis on the wetting kinetics, diffusion phenomenon and interfacial reaction of Sn–Bi–Zn solder on Cu substrate.Design/methodology/approachThe wetting kinetics, diffusion phenomenon and interfacial reaction of Sn–Bi–Zn solder on Cu substrate were analyzed by experiments. The interface was observed by scanning electron microscope to study the effect of Zn content on its interface.FindingsWith the increase in brazing temperature, the final spreading equivalent radius of the solder increases significantly, and the final contact angle of the solder decreases significantly. In addition, when the Zn content is 1%, the spreading effect of solder is the best, the equivalent radius is the largest and the contact angle is the smallest. According to the microstructural analysis, the thick intermetallic compounds layer of the Sn–15Bi–xZn solders on the Cu substrate can be effectively decreased by adding appropriate Zn content.Originality/valueThe wetting kinetics, diffusion phenomenon and interfacial reaction of Sn–15Bi–xZn solder on Cu substrate at different temperatures have not been studied yet.

Thermal and non-thermal effects of Cu/Al laminated composite during electrically assisted tension

The electrically assisted (EA) forming technology is expected to further explore the forming potential of Cu/Al laminated composite (LC). However, the current action mechanism in the forming process of Cu/Al LC is still unclear. In this paper, the influence mechanism of thermal effect and non-thermal effect on the dislocation structure of Cu/Al LC during EA tensile process was mainly studied. The results demonstrated that there was an obvious non-thermal effect in EA tensile Cu/Al LC. The flow stress reduction of EA tensile specimens was more significant than that of thermal assisted tensile specimens at the matching temperature. At the same time, the dislocation generated by the Frank-Read dislocation source and the Lattice distortion degree near the Frank-Read source was decreased by electric current. The decrease of dislocation density caused by the annihilation of the dislocations in the EA tensile process leads to the reduction of flow stress in the Cu/Al LC. In addition, the Cu matrix and the interface region dislocation lines of the EA tensile specimen were rearranged along the direction of electron movement and the crack tip healing in the intermetallic compound layer was promoted. What is more, the junction of phase layer becomes a new crack source due to the resistance being higher at the heterogeneous junction.

Interfacial reaction behavior and thermodynamics between Sn-xSb alloys and Cu substrate

In order to determine the effect of Sb element on the welding reliability of Sn-Sb alloy solder, the interfacial behavior of Sn-Sb alloys with different Sb contents on the Cu substrate was investigated. The evolution process of interfacial layers was explained by analyzing the microstructure and interfacial reaction thermodynamics of Sn-xSb/Cu system. The addition of Sb has a non-monotonic effect on the intermetallic compound layers. Sb can inhibit the diffusion of Cu into solder. The addition of 3 wt.% Sb in the alloy reduces the activation energy of interfacial reaction from 286.41 to 62 kJ/mol, which promotes the interfacial reaction. The addition of 10 wt.% Sb increases the activation energy of interfacial reaction to 686.73 kJ/mol, which inhibits the interfacial reaction and reduces the erosion of the Cu substrate by the solder and inhibits the formation of an excessively thick interfacial layer.

Microstructure and Mechanical Properties of TA2/Q235 Laser Weld Joint with Copper Interlayer.

For the dissimilar metal welding needs of TA2 titanium and Q235 steel, preliminary trials were conducted using laser welding methods, and the results showed that the addition of a copper interlayer and the bias of the laser beam toward the Q235 side allowed for an effective connection. The welding temperature field was simulated using the finite element method, and the optimum offset distance of 0.3 mm was obtained. Under the optimized parameters, the joint had good metallurgical bonding. Further SEM analysis showed that the microstructure of the bonding area between the weld bead and Q235 was a typical fusion weld pattern, while that of the bonding area between the weld bead and TA2 was in brazing mode. The microhardness of the cross-section showed complex fluctuations; the microhardness of the weld bead center was higher than that of the base metal due to the formation of a mixture microstructure of copper and dendritic Fe phases. The copper layer not involved in the weld pool mixing had almost the lowest microhardness. The highest microhardness was found at the bonding site of TA2 and the weld bead, mainly due to the formation of an intermetallic layer with a thickness of about 100 μm. Further detailed analysis revealed that the compounds included Ti2Cu, TiCu and TiCu2, showing a typical peritectic morphology. The tensile strength of the joint was approximately 317.6 MPa, reaching 82.71% of that of the Q235 and 75.44% of the TA2 base metal, respectively. The fracture occurred in the unmixed copper layer.

Mechanical behavior of AA5083/AA6061 friction stir welds using modal analysis

Abstract Solid-state joining is used for welding similar or dissimilar materials due to its many advantages like avoiding fusion and formation of a thick intermetallic layer, etc. Determination of the right process parameters (feed rate and rotation speed) and tool geometry (shoulder and pin) is of critical importance in friction stir welding in order to achieve adequate weld quality. The experiments were performed using three process parameters: feed rate (mm min−1), rotation speed (rpm) and pin geometry for friction stir welding of Al5083 and Al6061. Eighteen experiments were performed with different process parameters and mechanical tests (microhardness and tensile measurements) have been carried out to determine the weld quality. Results showed that the best results of ultimate strength (198.5 MPa) were achieved by the triangle pin geometry, 1250 rpm rotation speed and 100 mm min−1 feed rate. Similar results were observed in microhardness tests. Effects of tool geometry, feed rate, and rotation speed on the vibration properties and weld quality are also investigated experimentally. The effects of the FSW parameters used were assessed using vibration analysis.

Microstructural evolutions and mechanical characteristics of roll-bonding Mg/Al clad plate regulated by cold spraying micron particle interlayer

A new process of “cold spraying interlayer + roll-bonding” (CSIR) was put forward for the preparation of Mg/Al clad plates. First, the micron Ni and Al powders (including some Zn particles) were cold sprayed to form an ultrathin coating on Al or Mg substrate slabs. Then roll-bonding was performed at 400 °C. The influence of cold sprayed coating on slab surfaces, interfacial microstructures, texture evolutions, mechanical properties and the related mechanism were systematically investigated. The results show that the average shear strength of the as-rolled Mg/Al clad plate assisted by cold spraying Al and Ni micron powders interlayer on the substrate slabs was nearly twice (35.58 MPa) than that of conventional rolling under the same conditions (single pass, reduction ratio was 35%). For as-rolled Mg/Al clad plates, almost no reaction diffusion layers are generated, and the mechanical interlocking between cold sprayed coatings and substrate slabs is the main mechanism for improving the shear strength. The interface between the Al coating and the Ni coating is weakest of the as-rolled Mg/Al clad plates. As the reduction rate increases from 27.5% to 47.5%, the function of the mechanical interlocking of cold sprayed coatings will first increase and then weaken. After annealing at 400 °C for 1 h, the interface between the Al coating and the Mg substrate slab will form thick mixed brittle intermetallic compounds, including Al3Mg2, Mg17Al12, MgZn2 and AlMg4Zn11, and cause local gaps, holes, and cracks around the Zn-rich Ni coating. The fracture path after annealing starts from the vicinity of the defective Ni particles, and eventually enlarges along the mixed intermetallic compounds layer between the Al coating and the Mg substrate slab. The research indicates that the CSIR process has great potential in cooperating the metallurgical bonding with the mechanical interlocking of clad plates.

Inhibiting effect of Ni/Re diffusion barrier on the interdiffusion between Ni-based coating and titanium alloys

A Ni/Re layer was electroplated as a diffusion barrier between the Ni coating and TC4 substrate. Isothermal diffusion treatments for the specimens with or without diffusion barriers were conducted at 600 ℃ at different times. Besides, the interdiffusion behaviors and the growth of the intermetallic layers were investigated. Results showed that the Ni/Re layer played a superior barrier effect, which inhibited the interdiffusion and retarded the formation of the interdiffusion zone. Moreover, the relationship between the thickness of the interdiffusion zone and the annealing time conformed to the parabolic law, and the square of the thickness of the intermetallic layer was proportional to the annealing time. Besides, the inhibiting mechanism of the Ni/Re diffusion barrier was discussed in detail.