Thin Intermetallic Compound Layer Research Articles

КИНЕТИКА РОСТА ДИФФУЗИОННЫХ ПРОСЛОЕК В СКМ 20880+АД1+ВТ1-0

It is shown that the diffusion zone at the interlayer boundary of steel 20880 + aluminum AD1 consists of two layers: the Fe2Al5 intermetallic compound located on the steel side and constituting the main part of the diffusion zone, and a thin (up to 10 μm) layer of the FeAl3 intermetallic compound on the aluminum side. Microhardness of the diffusion zone ~ 12 GPa. It has been established that the intensity of growth of the diffusion zone at the interlayer boundary of aluminum AD1 + titanium VT1-0 with the phase composition TiAl3 is almost one and a half times lower than at the interlayer boundary of steel 20880 + aluminum AD1. Its microhardness is ~5 GPa.

Interfacial microstructure and mechanical property of dissimilar resistance spot welded joint of TC4 titanium alloy and 316L stainless steel with nickel interlayer

Dissimilar materials of TC4 titanium alloy and 316L stainless steel were joined by means of resistance spot welding with nickel interlayer in different thicknesses. A significant enhancement in terms of nugget morphology quality with less defects was achieved for the welded joints with nickel interlayer compared with that without interlayer. With increasing the nickel interlayer thickness from 50 μm to 300 μm, the effective nugget diameter increased gradually from ∼4.8 mm to ∼5.2 mm, which was lower than that of the interlayer-free welded joint being ∼5.9 mm. A thinner intermetallic compound layer with dual-layered structure features with thickness of ∼11 μm was formed at the nugget/titanium interface in the welded joint with nickel interlayer compared with that of the interlayer-free welded joint, meanwhile an intermetallic compound layer with thickness of ∼3 μm was formed at the nugget/stainless steel interface, which exhibited serrated structure features. The introduction of nickel interlayer in the welded joint could suppress the formation of the brittle Ti–Fe intermetallics such as Fe2Ti, and facilitate the formation of TiNi, Ti2Ni and TiNi3. A more homogeneous current density distribution and a lower peak temperature (1809 °C) during welding were achieved via employing nickel interlayer. With increasing nickel interlayer thickness from 0 μm to 300 μm, the tensile shear load of welded joints experienced an increased tendency first and then decreased, meanwhile the maximum tensile shear load of 3.7 kN was obtained with the interlayer thickness of 200 μm, which was 61% higher than that of the interlayer-free welded joint.

Brittle Fracture Behavior of Sn-Ag-Cu Solder Joints with Ni-Less Surface Finish via Laser-Assisted Bonding.

In this study, we investigated the brittle fracture behavior of Sn-3.0Ag-0.5Cu (SAC305) solder joints with a Direct Electroless Gold (DEG) surface finish, formed using laser-assisted bonding (LAB) and mass reflow (MR) techniques. Commercial SAC305 solder balls were used to ensure consistency. LAB increases void fractions and coarsens the primary β-Sn phase with higher laser power, resulting in a larger eutectic network area fraction. In contrast, MR produces solder joints with minimal voids and a thicker intermetallic compound (IMC) layer. LAB-formed joints exhibit higher high-speed shear strength and lower brittle fracture rates compared to MR. The key factor in the reduced brittle fracture in LAB joints is the thinner IMC layer at the joint interface. This study highlights the potential of LAB in enhancing the mechanical reliability of solder joints in advanced electronic packaging applications.

Crack initiation and propagation behavior of dissimilar interface with intermetallic compound layer in Al/steel joint using coupled multiscale mechanical testing

We demonstrate multiscale mechanical testing using miniature and microscale tensile tests to elucidate the crack initiation and propagation behaviors corresponding to interfacial nanostructures in dissimilar joints of 6061 aluminum alloy and 304 stainless steel. The initial nucleation and subsequent growth of intermetallic compounds (IMCs) can be controlled by heat treatment after friction stir lap welding. The miniature tensile tests exhibited the relationship between the joint strength and IMC layer thickness with changes in the fracture location. Microscale tensile testing using a single edge-notch tension geometry initiates the crack and subsequent propagations near the interface, which helps identify the crack initiation site and understand the dependence of the local strength on the type of IMCs. Crack deviation behavior toward the Al side, attributed to the difference of local strength, is confirmed by in situ observations, which indicated that continuous failure can easily occur within the grown IMCs, particularly in macroscale joints. It was concluded that the crack propagation is controlled by the local crack deviation toward metal matrix, which tends to occur for the dissimilar interface with thin IMC layer. This miniature/microscale tensile testing approach is expected to clarify the essential relationship between the interfacial microstructure and the fracture behavior.

Kinetics of intermetallic compound layers between AISI 321 stainless steel and molten aluminum

The interfacial reaction between liquid aluminum and solid steel is critical to understanding the evolution of intermetallic compounds (IMCs) in the brazing and weld brazing processes of aluminum-to-steel dissimilar alloys. In this study, hot dip aluminizing of AISI 321 stainless steel at different temperatures was conducted to reveal the influence of reaction temperature and time on interfacial IMCs. Electron microscopy analyses were employed to investigate the interfacial microstructures. A single layer of θ-Fe4Al13 was observed at 700°C. In contrast, the IMCs of interfaces dipped at 800–1000°C consisted of a thin inner layer of η-Fe2Al5 + ζ-FeAl2 next to the steel and a thick layer of θ-Fe4Al13 close to the aluminum. For the inner layer, the thickness increased with increasing dipping temperature and time. Its growth was described by a parabolic rate law, which suggested a diffusion-controlled mechanism at the interface. An activation energy of 66.5 kJ mol−1 was obtained. For the Fe4Al13 layer, the thickness evolution at different temperatures was different from that of the inner layer, with a thick IMC layer at 700°C, a thinner IMC layer at intermediate temperatures (from 800 to 900°C), and a slightly thicker IMC layer from 950 to 1000°C. The growth kinetics of Fe4Al13 at 700°C were controlled by diffusion, interfacial reactions, and dissolution mechanisms. The evolution of Fe4Al13 between 800 and 1000°C was governed by diffusion and dissolution mechanisms. The appearance of the inner layer and the evolution kinetics of Fe4Al13 accounted for the decrease in thickness with increasing temperature between 700 and 900°C.

Friction stir welding of AA5010 aluminum alloy to St-12 carbon steel using CoCrCuFeNi high entropy alloy interlayer

Dissimilar friction stir welding (FSW) of AA5010 aluminum alloy to St-12 carbon steel using an equiatomic CoCrCuFeNi high-entropy alloy (HEA) interlayer was investigated. Mechanical properties of the joints fabricated under different plunge depths of the FSW tool were examined and correlated to microstructural evolutions. The incorporation of the HEA interlayer successfully prohibited the formation of AlFe intermetallic compounds (IMCs). Also, the interlayer was metallurgically consistent with both base metals, although quite thin complex IMC layer was formed at the aluminum/HEA interface as a result of sluggish diffusion of constituent elements of HEA towards the aluminum. The application of suitable plunge depth in the steel part, i.e. 0.2 mm, resulted in the perturbation of the HEA/steel interface and then the formation of interfacial mechanical interlocks that were beneficial to the strength of the joints. However, excessive FSW tool plunge depth caused large voids to form near hooks, acting as stress concentration areas during shear-tensile test. An appropriate plunge depth of the tool achieved an ideal joint that exhibited fracture from the aluminum side rather than the joint interfaces. It also provided a strength value as high as 80 % of the nominal strength of aluminum base metal.

Acoustic effect on the joint quality and process of friction stir lap welding of aluminum to steel

To gain a high strength-to-weight ratio and economic viability for multiple industrial applications, the Al and steel need to be joined successfully. In the present work, we used conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW) techniques to obtain high-strength industrial-grade dissimilar joints of Al and steel. The effects of acoustic energy on the joint quality and welding process were investigated. Macrographs of the joints revealed that ultrasonic vibrations could effectively promote the material flow and increase the mixing degree and width of the Al/steel interface. Steel strips' fragmentation and intermixing with the Al substrate were enhanced under ultrasonic effects. The tool torque, axial force, and spindle power were significantly decreased with ultrasonic vibration. Acoustic assistance was found beneficial to increase the joints’ failure load and change the fracture mechanism. The microhardness of acoustically treated regions was found to be higher compared to its counterparts. The thinning of the brittle intermetallic compounds (IMCs) layer at the interface of the UVeFSW joint was caused by decreased peak temperature during welding. In UVeFSW, when the welding speed was 50 mm/min, the maximum failure load of the joint was obtained under the joint action of the macro interlocks (interface zone), the thinner IMCs layer, and the micro interlocks (laminated structure). When the welding speed was 100 mm/min, the failure load of the joint was improved by 25.8% compared with conventional FSW.

Suppression of discontinuous precipitation and strength improvement by Sc doping in Cu-6 wt%Ag alloys

• Sc doping significantly suppressed discontinuous Ag precipitates in Cu-Ag alloys. • Sc-doping led to a 55 MPa increase in strength, with only a slight decrease in conductivity. • Sc segregation at grain boundaries inhibited the nucleation of discontinuous precipitates • The UTS of Sc-doped samples was 1080 MPa, 205 MPa higher than that of non-doped samples. In low-Ag Cu matrix alloys, the presence of coarse discontinuous precipitates may limit strength. We demonstrated that discontinuous precipitation was suppressed, and continuous precipitation was enhanced by the doping of Cu-6 wt%Ag with Sc. A high-volume fraction of continuous precipitates, which nucleated on {111} planes, led to a 55 MPa increase in strength, with only a slight decrease in electrical conductivity. The addition of Sc inhibited the nucleation of discontinuous precipitates by causing the Sc and the Ag to co-segregate onto grain boundaries, thus forming a thin intermetallic compound layer between grains. After deformation, both discontinuous and continuous precipitates were drawn into Ag fibers. The combination of deformation strain and doping caused an increase in density and a decrease in the diameter of Ag fibers, resulting in about 205 MPa increase in doped samples when the deformation strain reached 4.9. The thinner, denser Ag fibers in the doped samples also caused higher electron scattering at interfaces, leading to electrical conductivity that was 11% IACS lower than in non-doped samples. For reference, 100% IACS (International Annealed Copper Standard) is equivalent to 1.7241 μΩ cm.

Fatigue behavior of three-sheet aluminum-steel dissimilar resistance spot welds for automotive applications

Responding to the increasing demand of multi-material solutions for structural lightweighting in automotive industry, resistance spot welding (RSW) of two sheets, e.g. aluminum to aluminum, or aluminum to steel, has been successfully developed and implemented in production using novel multi-ring domed (MRD) electrodes and multiple solidification weld schedules. In this study, we report, for the first time, the successful RSW of three sheets, i.e. 1.2 mm thick AA6022 to 0.65 mm thick high strength low alloy (HSLA) steel and 1.4 mm thick CR780T steel sheets. The resultant RSWs formed a thin layer of intermetallic compound between the aluminum-steel interface and a much smaller but completely melted weld nugget between the two steels, achieving an acceptable joint strength com-pared to RSWs of 1.2 mm thick AA6022 to itself and 1.2 mm thick AA6022 to 2.0 mm thick HSLA. Fatigue test results show that the three-sheet RSWs reached comparable fatigue behavior to that of 1.2 mm AA6022 to 2.0 mm HSLA. Using the structural stress analysis, all the fatigue data fall onto one master curve indicating that the aluminum-steel weld nugget diameter dominates the fatigue life.

Achievement of high-strength Al/Cu dissimilar joint during submerged friction stir welding and its regulation mechanism of intermetallic compounds layer

The control of intermetallic compounds (IMCs) is the key to achieve high-performance Al/Cu dissimilar joints. In the present study, the dissimilar metals of 6061-T6 Al and T2 pure Cu were joined by submerged friction stir welding (SFSW) technology. The results indicated that the peak temperature and dwelling time at high temperature were obviously reduced by applying additional water cooling in SFSW. In comparison to the joint fabricated by normal friction stir welding (FSW), the thickness of IMCs layer at the interface for the SFSW joint was much thinner and its distribution was more uniform, the formation of IMCs was effectively inhibited during the SFSW process. The Al2Cu phase was first formed at the Al/Cu interface, and then Al4Cu9 phase precipitated between Al2Cu phase and Cu. The tensile properties of the Al/Cu joints were significantly improved by the SFSW process. The maximum tensile strength of 255 MPa was obtained in the SFSW joint, which was 41.7% higher than that of the FSW joint. A higher joint efficiency of 91.1% was reached, which was due to the reduced stress concentration at the interface in SFSW caused by the thinner IMCs layer and lower welding heat input. The fracture occurs within Al2Cu phase or along the interface between Al and Al2Cu layer for the FSW joint. In contrast, the SFSW joint fractures at the HAZ on Cu side, showing favorable ductility.

Microstructural and Mechanical Properties of AZ31B to AA6061 Dissimilar Joints Fabricated by Refill Friction Stir Spot Welding

Dissimilar friction stir spot welds (FSSW) between the magnesium and aluminum alloys are joined, using a novel approach called refill friction stir spot welding. The present work aims to evaluate the macrostructural and mechanical properties of refill friction stir spot welded AZ31B and AA 6061-T6 alloys in two combinations, i.e., identical Mg-to-Mg and dissimilar Mg-to-Al joints, and the results are compared with the results obtained in conventional friction stir spot welding. The hardness profiles of the similar welds had the appearance of a W-shape, and the Thermo mechanically affected zone and heat-affected zone of both methods had lower hardness values than the rest of the weld. Along with the interface between the aluminum and magnesium sheets, a thin intermetallic compound layer of Al12Mg17 has been identified, which has led to an increase in hardness. The static shear strength of both similar and dissimilar refill spot friction welds was much greater than that of traditional spot friction welds. In both similar and dissimilar spot friction welds, two distinct failure scenarios are discovered.

Effect of Ni Addition on the Interfacial Strength of Al/Cu Dissimilar Welds Produced by Friction Stir Lap Welding

Al/Cu dissimilar joining is a key technology for reducing the weight and cost of electrical components. In this study, the dissimilar friction stir lap welding (FSLW) of a Ni-containing Al alloy to pure Cu was performed, and the effects of the addition of Ni on the weld strength and interfacial microstructure were examined. A thin intermetallic compound (IMC) layer was observed at the Al/Cu weld interface produced by FSLW. The addition of 3 at.% Ni effectively improved the weld strength, although the thickness of the IMC layer increased. The IMC layer formed at the Al/Cu interface without Ni comprised CuAl2 and Cu9Al4 from the pure Al side. In contrast, the IMC layer formed with 3 at.% Ni consisted of (Ni,Cu)Al, CuAl, and Cu9Al4 from the Al side. The addition of Ni eliminated the weak CuAl2/Cu9Al4 interface, thereby improving the weld strength. The results of this study suggest that the strength of the Al/Cu weld can be effectively improved by the thinning of the IMC layer caused by FSLW and the change in interfacial microstructure caused by Ni addition.

Improving the Quality of Dissimilar Al/Steel Butt-Lap Joint via Ultrasonic-Assisted Friction Stir Welding

A dissimilar AA7075/Q235 butt-lap joint was fabricated via ultrasonic-assisted friction stir welding (UaFSW), and the characteristics of the UaFSW joint were investigated systematically. The acoustoplastic effect of the ultrasonic vibration led to the softening of the materials and enhanced the material flow during welding, decreasing the volume of welding defects in the nugget zone of the UaFSW joint. With the help of ultrasonic vibration, a smooth and thin intermetallic compounds (IMCs) layer could generate along the Al/steel interface at the top of nugget zone, which possibly consisted of Al5Fe2 and Al13Fe4 phases. However, the positive effects of the ultrasonic vibration were weakened at low temperatures; consequently, the IMCs layer became discontinuous at the bottom of the nugget zone and the welding defects also formed. The ultrasonic vibration accelerated the dynamic recrystallization and refined the microstructures in the nugget zone due to the increased strain rate and stored energy. As a result, the UaFSW joint exhibited a better mechanical performance in comparison to the FSW joint, and the increment in the peak tensile load/elongation was more than twice. In addition, the UaFSW joint failed in the nugget zone along with the Al/steel interface, and the fracture mode was a mixture of ductile and brittle.

Influence of Filler Alloy on Microstructure and Properties of Induction Brazed Al/Cu Joints

This work aimed to clarity the influence of filler alloy on microstructures and properties of induction brazed Al/Cu joints. It was found that the alloying elements in the filler alloy changed the morphology and phase type of interfacial layer in the joint. Mg converted the native Al2O3 film into MgO and stopped the re-oxidation of aluminum. However, excessive Mg caused planar inter-metallic compounds (IMCs) to become wavy, which decrease the ductility of the joint. A suitable amount of Cu and Si removed residual oxide film and resulted in a thin planar IMCs layer, which is beneficial to Al/Cu joint. Al-8Si-4Cu-2Mg-1Ga-0.05Ce filler foil produced an excellent joint consisting of a 2μm Cu9Al4/CuAl2 planar layer and free from oxide film. The tensile strength of the joint is higher than that of aluminum. The bend angle is higher 130°. The electrical resistivity of the joint is lower than the theoretical value.

Laser pressure welding of dissimilar aluminium and copper: microstructure and mechanical property

In this work, laser pressure welding of dissimilar aluminium and copper was conducted at a high welding speed of 15 m min−1. One-micron intermetallic compounds (IMCs) layer with heterogeneous dual-phases (copper and γ-Al4Cu9 phases) laminates in the joint interface were observed by transmission electron microscopy. The results showed that the combination of two joining mechanisms led to improved mechanical property, namely the mechanical interlocking due to the curved interface and the metallurgical bonding by the presence of the thin IMCs layer with heterogeneous laminates. The tensile shear force and the shear strength of the joint reached 2055 N and 111.94 MPa, respectively. The present study provides a more efficient method to join dissimilar aluminium and copper.

Microstructure characteristics and mechanical properties of the Cu/Al dissimilar joints by electric current assisted ultrasonic welding

Dissimilar joints of copper and aluminium alloy were generated by electric current assisted ultrasonic welding (EUSW). The microstructure characteristics and mechanical properties of Cu/Al EUSW joints were systematically investigated. The electric current promoted the plastic flow at the welding interface. The intermetallic thickness increased with electric current. The microstructure characteristics of Cu/Al joints welded by EUSW were compared with those of the Cu/Al joints welded by ultrasonic welding (USW). A thinner intermetallic compound layer could be obtained at the more fully material mixing during EUSW. The Cu/Al joints welded by EUSW displayed ultimate tensile strength 12% and fracture energy 21% greater than those of the Cu/Al joints welded by USW. The reasons for the improvement in mechanical properties of the Cu/Al EUSW joints have been discussed.

Effect of microwave operating power and reflow time on the microstructure and tensile properties of Sn–3.0Ag–0.5Cu/Cu solder joints

PurposeThis paper aims to investigate the morphology and tensile properties of SAC305 solder alloy under the influence of microwave hybrid heating (MHH) for soldering at different microwave parameters.Design/methodology/approachSi wafer was used as susceptor in MHH for solder reflow. Microwave operating power for medium and high ranging from 40 to 140 s reflow time was used to investigate their effect on the microstructure and strength of SAC305/Cu solder joints. The morphology and elemental composition of the intermetallic compound (IMC) joint were evaluated on the top surface and cross-sectional view.FindingsIMC formation transformed from scallop-like to elongated scallop-like structure for medium operating power and scallop-like to planar-like structure for high operating power when exposed to longer reflow time. Compositional and phase analysis confirmed that the observed IMCs consist of Cu6Sn5, Cu3Sn and Ag3Sn. A thinner IMC layer was formed at medium operating power, 80 s (2.4 µm), and high operating power, 40 s (2.5 µm). The ultimate tensile strength at high operating power, 40 s (45.5 MPa), was 44.9% greater than that at medium operating power, 80 s (31.4 MPa).Originality/valueMicrowave parameters with the influence of Si wafer in MHH in soldering have been developed and optimized. A microwave temperature profile was established to select the appropriate parameter for solder reflow. For this MHH soldering method, the higher operating power and shorter reflow time are preferable.

Interfacial microstructure and mechanical property in friction stir welded Mg/Al joints under low rotation speed

The variation of interface microstructure along thickness direction and the associated effects on tensile strength were studied. Thin intermetallic compounds (IMC) layer, ranging from 700 nm to 2 μm, formed through solid-state diffusion instead of eutectic reaction under low rotation speed of 300 rev min−1. It was consisted of Al3Mg2 sublayer and Mg17Al12 sublayer, with Mg17Al12 sublayer thinner than Al3Mg2 sublayer. IMC layer in the upper part is thinner than that in the middle part, and it is continuous in the upper and middle part while discontinuous near the bottom surface. Despite the difference in interface microstructure, the bonding strengths of upper part and middle part are similar, proving the important effects of macroscopic geometrical configuration of the interface.

Acoustic effect on the tensile properties and metallurgical structures of dissimilar friction stir welding joints of Al/Mg alloys

Abstract The joint strength of friction stir welded Al/Mg alloys is a critical factor for the wide applications of dissimilar joints. In this study, dissimilar Al/Mg alloys joints were made by friction stir welding (FSW) and its variant, ultrasonic vibration enhanced FSW (UVeFSW), respectively. The tensile strength, fracture toughness and fracture location of the whole joints and three (upper, middle, lower) parts of the joints were compared by characterizing the macro-, mesoscopic- and micro-structures of the welds. The influence of ultrasonic vibration on the tensile properties of the joints was discussed. The results showed that the lower part of the welds was the weakest part due to the poor materials mixing/interlocking and a large amount of intermetallic compounds, while the upper part of the weld had the best strength. Good material mixing/mechanical interlocking in the welds was the basis for obtaining higher joint strength, and the thinner intermetallic compound layer was the key to the better toughness of the joint. The application of ultrasonic vibration can improve the tensile strength of each part of the welds, but the improvement rate of tensile strength is greater for the middle and lower parts of the welds.

Interface strengthening of a roll-bonded two-ply Al/Cu sheet by short annealing

We investigated the influence of annealing on the microstructural evolution and mechanical properties of a roll-bonded two-ply clad sheet made of aluminum and copper alloys. Various microstructures were obtained via heat treatment at 400 °C. Initially Al2Cu and Al4Cu9 phases were indexed at interface whose overall thickness was 1 μm by annealing for 20 min. By the progress of annealing for 120 min, another thin intermetallic compound (IMC) layer, AlCu phase, was formed between initially generated Al2Cu and Al4Cu9 layers. Total thickness of IMCs was considerably increased by 3.12 ± 0.24 μm. Uniaxial tensile and peel tests were performed and the results indicated simultaneous improvements of the bonding strength and elongation without much expense of tensile strength by suitable short-time annealing for 10 min at 400 °C, where the aluminum‑copper joint kept its mechanical integrity when the overall thickness of intermetallic compound layers limited less than 1 μm.