Copper Joints Research Articles

Effect of Different Welding Speeds on Microstructure and Properties of Bobbin Tool Friction Stir Welded Joints of T2 Pure Copper

Effect of Different Welding Speeds on Microstructure and Properties of Bobbin Tool Friction Stir Welded Joints of T2 Pure Copper

Effect of Ga on microstructure and properties of Ag50CuSn12 and Al2O3/oxygen-free copper welds

The effects of Ga on the properties of Ag50CuSn12 and brazed joints were studied. The results show that Ga can reduce the melting temperature of the Ag50CuSn12 and improve its wettability. With the increase of Ga content, the spreading area of the solder increases first and then decreases. And the spreading area is the largest when the content of Ga is 3 wt%, which is 48% higher than that without Ga. Ga plays an important role in grain refinement of weld microstructure. The size of the block particles in the weld decreases accompanied by the increase of Ga. The fine strip grains increase is evenly distributed. The refinement effect is also the best when the Ga content is 3 wt%. For this reason, the shear strength of the brazed joint of Al2O3 and oxygen-free copper increases first and then decreases. When the Ga content is 3 wt%, the shear strength is the highest, which is 2.2 times that of the joint without Ga.The analysis suggests that the incorporation of Ga lowers the melting point of the solder, improves its oxidation resistance, and reduces its surface tension and viscosity, thereby enhancing its wettability and diffusivity. However, excessive Ga can hinder the solder's spread.

Microstructure and mechanical properties of Al2O3 ceramic and copper joints brazed with AgCuInTi brazing alloy

AbstractReliable metallurgical bonding between Al2O3 ceramic and copper was achieved by vacuum brazing using Ag–23Cu–14.5In–3.3Ti (wt.%) alloy. The representative interfacial structure of the joint was Al2O3/Ti3(Cu,Al)3O + γ‐TiO/Ag‐based solid solution + (Cu,Ag)7In3 + Ag–Cu eutectic + Cu‐based solid solution/copper. The interface microstructure evolved with process parameters, including the formation of γ‐TiO and Ti3(Cu,Al)3O, as evidenced by microstructural analysis and etched surface morphology. The relationship between fracture path and shear strength was established by observing the fracture morphology and performing shear strength tests on joints with various process parameters, utilizing the degree of the Ag‐based solid solution loss and the thickness of the reaction layer as evaluative factors. When brazed at 760 or 780°C for 20 min using a 100 µm brazing alloy foil, the brazed joints demonstrated a peak shear strength of 215 ± 25 MPa, and the fracture predominantly occurred in the Al2O3 matrix and Ti3(Cu,Al)3O layer.

Corrosion behavior of AA2024/pure copper bimetal manufactured by friction stir welding with a hybrid zinc-graphite interlayer

The effect of utilization of zinc (Zn) and graphite (Gr) as a hybrid interlayer for dissimilar lap joint of AA2024 and pure copper, employing friction stir welding (FSW), was investigated in this study. The microstructure of the samples was examined using a scanning electron microscope (SEM), and the composition of the present phases was evaluated with energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were performed to analyze the corrosion behavior. Subsequently, the post-corrosion morphology was examined using SEM and EDS. The results show that applying two passes of FSW in the presence of hybrid Zn-Gr interlayer, led to the modification of detrimental brittle intermetallic compounds (IMCs). The corrosion investigations demonstrated that the corrosion current density (icorr) in the AA2024/(Zn-Gr)/Cu sample after 1- pass FSW was reduced by about 80% in comparison to the Al/Zn/Cu sample. This behavior can be attributed to the presence of a large number of diffusion channels and the inhibitory effect of graphite particles. The 2-pass FSWed AA2024/(Zn-Gr)/Cu sample exhibited the highest level of corrosion resistance, owing to the better dispersion of graphite particles, which led to improved passivation on the aluminum side. As a result, the inherent issue of intergranular corrosion in the Al–Cu alloy was effectively resolved at the joint interface. This ultimately led to an enhanced corrosion resistance of the Al–Cu bimetals produced by FSW.

Assessing Tensile Strength and Electrical Conductivity of Friction Stir-Welded Joints of Copper and Aluminum Alloys

Dissimilar aluminum joints have widespread applications across various industries, including the electronics and automotive sectors, owing to their unique combination of advantages, including reduced density and enhanced mechanical properties. These characteristics make them an innovative solution for multi-material processing challenges presented in the engineering industry. This article focuses on Friction Stir-Welded butt joints made using a weld–flip–weld approach between aluminum AA6061-T6 and pure copper C11000, exploring the effects of varying rotational speeds (1000, 1200, and 1400 RPM), offsets (0 and 1 mm) in the joint soundness, mechanical strength, and electrical conductivity. The welds were evaluated using non-destructive testing with phased-array ultrasound and tensile testing. Additionally, the electrical conductivity was measured to assess their response to electrical currents. The findings reveal a significant correlation between joint efficiency and electrical conductivity, with the highest values corresponding to a weld executed with a rotational speed of 1400 rpm, traverse speed of 40 mm/min, and 1 mm offset towards the aluminum, achieving the highest joint efficiency, reaching a joint efficiency of approximately 75% and 82.42% of the IACS for electrical conductivity.

Impact of Hydrogen Voiding in Chip-to-Chip Electroless All-Copper Interconnections.

Three-dimensional (3D) integration has become a leading approach in chip packaging. The interconnection density and reliability of micro-bumps in chip stacking are often threatened by high bonding temperatures. The method of building chip-to-chip interconnections by electroless deposition of metal has its distinct merit, while the interfacial defect issue, especially that related to voiding during the merging of opposite sides, remains largely unsolved. In this study, to trace the influencing factors in the voiding, the growth characteristics of the electroless all-copper interconnections were examined by carrying out deposition experiments in a microfluidic channel device. The results show that when the gap between the opposite copper bumps to be electrolessly merged is as low as 10 μm, significant voids appear at the inflow side and the top of the copper bumps because the hydrogen cannot be expelled in time. A finite-element flow model of the plating solution between the chips was established, which showed that the flow rate of the plating solution around the copper bumps was much higher than in the merging gap, causing an uneven supply of reactants. Based on these findings, we proposed two potential solutions, one is to improve the flow mode of the plating solution, and the other is to add the reaction inhibitor, 2,2'-bipyridine. Finally, the combination of these two approaches successfully achieved an improved merging quality of the copper joints.

Improvement in weld quality of Al and Cu joints using dual-beam laser welding

The high weld quality of dissimilar aluminum (Al)/copper (Cu) joint is essential to improve the reliability of connecting components in secondary batteries. This study was aimed at enhancing the weld quality of dissimilar AlCu joints to connect tab-to-busbar in secondary batteries. AA1050 and Ni-coated Cu (C1100) sheets were lap-welded using dual-beam laser welding with a continuous-wave (CW) laser for welding and a pulsed laser for preheating. Consequently, the weld quality was investigated by characterizing the morphology, microstructure, and mechanical and electrical properties of the joints. For comparison of the weld quality, single-beam welding was also performed. Soundly welded joints were achieved using a dual-beam at a CW laser power range of 1000–1400 W for fixed pulsed laser power and welding speed of 100 W and 80 mm/s, respectively. Microstructural analysis of the weld indicated that the upper weld metal (WM) comprised α-Al and AlCu eutectic phases, whereas the lower WM exhibited mixed morphology of different phases including Al2Cu, AlCu, Al3Cu4, and Al4Cu9. Further, the electrical resistance was linearly correlated with weld penetration depth, exhibiting a minimum of 352.3 μΩ against a penetration depth of 341.7 μm. In addition, The Vickers microhardness and lap shear tensile testing of soundly welded sample (A4) exhibited an average hardness value of 921.7 HV in the lower WM, and the average tensile load for the welded sample was 247.4 N. This study provides valuable insights for improving the weld quality of reliable AlCu dissimilar joints for connecting tab-to-busbar in secondary batteries.

Investigations on mechanical features and mechanical performance of rotary friction welded Al-Cu joint at optimized conditions

In this experimental investigation, rotary friction welding (RFW) was employed to fabricate dissimilar Al-Cu joints, and the RFW variables were rotated against the ultimate tensile strength (UTS) in an effort to strengthen the dissimilar AA1100 and pure copper (Al-Cu) joint using response surface methodology (RSM) with a three-factorial design. Following this, micro-hardness, metallurgical characterization, and fatigue properties studies were done on the dissimilar joints fabricated under the optimized conditions. As a result of this investigation, the UTS of 208 MPa was attained as a maximum as the rotation speed was set at 1800 rpm, the friction time was 10 s, and the forging load was 5 kN. The dissimilar joint exhibits a better fatigue strength of 98.5 MPa when compared to the AA1100 base metal. At optimized conditions, the feature of the fracture image was found to be brittle due to the development of new compounds in the weld interface. A significant dip in micro hardness (52 Hv) was noticed in the region that connects TMAZ and HAZ of the AA1100 side of the dissimilar joint, which was concluded to be the weakest zone as the dissimilar joints were fractured in the same location during the tensile test. The observed results benefit the automotive sector, especially when fabricating components that require effective thermal management and weight reduction, like electrical connectors, heat dissipation systems, and radiators. For heat exchanger applications, improved fatigue strength in dissimilar Al-Cu joints is important because it guarantees longer structural integrity and improved durability.

Mechanical behavior and failure mechanism of resistance spot welded Aluminum and Copper joint used in the lightweight structures

Mechanical behavior and failure mechanism of resistance spot welded Aluminum and Copper joint used in the lightweight structures

Interface regulation of micro-sized sintered Ag-10Al composite based on in-situ surface modification and enhanced microstructure stability in power electronic packaging

The increasing demand for high-power SiC semiconductors necessitate the development of a die attachment material that combines high-temperature resistance, reliability, and cost-effectiveness. In this study, a novel micro-sized composite, Ag-10Al paste, containing 10 wt% Al particles, was designed. A remarkable phenomenon, the ejection of ultrafine Ag nanoparticles from micron-sized Ag flakes, was observed for the first time. The phenomenon was utilized for the in-situ surface modification of Al. Subsequently, the microstructure and mechanical properties of the sintered Ag-10Al/direct bonded copper (DBC) joints were studied. Results indicated that the Ag-10Al composite exhibited superior microstructure stability compared to sintered Ag. The Ag/Al interface was systematically analyzed, revealing a unique Ag/nano Ag2O/Al2O3 amorphous/Al structure. This structure was formed through the Ag nanoparticle jetting effect of Ag flakes, achieving effective bonding between nano Ag2O and Al2O3 amorphous phases through mutual dissolution at the atomic level. Moreover, the sintered Ag-10Al joint demonstrated enhanced mechanical performance stability over the sintered Ag joint. After 1000 h aging at 300 ℃, the shear strength of the sintered Ag-10Al joint reached 34.1 MPa, meeting the requirements for power semiconductor packaging. In conclusion, the Ag-10Al composite paste was thoughtfully designed, excelling in both performance and cost-effectiveness.

Solder-less Fine Pitch Copper-to-Copper Bonding

The industry has been looking to increase pitch scaling through various methods. One of these methods is an alternative to solid-state solder bonding. However, very few processes can compete with solder bonding’s fast speed, low cost, and flexibility. The approach with the biggest potential for connecting fine pitch interconnects in high-density semiconductor packaging is solder-less copper-to-copper direct bonding. There are many benefits to using copper-to-copper direct bonding, including the ability to achieve ultra-fine-pitch (bump pitch 10 μm), higher reliability (both thermo-mechanically and better electromigration behavior), low resistance, as well as the lack of concern for solder hierarchy for multiple reflow. This copper-to-copper direct bonding technology enables a variety of 2.5D/3D advanced packaging architectures and is also suitable for multi-die stacking. In this study, we report the investigation of a direct copper-to-copper bonding methodology and reliability of the bonded components. Our process differs from common hybrid bonding copper-to-copper techniques, in that it is designed for low volume highly complex products. This technology allows a die-to-die and die-to-wafer process using thermocompression bonding under a deoxidizing vapor flow for direct copper-to-copper bonding. The process does not require high temperature oven annealing and can be done in a normal atmospheric environment. The investigated bonding process is ideal for high power, high thermal, high density 3D stacking and high-speed digital communication applications. We demonstrated the bonding procedure using a test vehicle with 40 μm diameter pillars and 80-μm bump pitch. We investigated the effects of bonding force and evaluated joint reliability. Interconnect/bond strength was determined through destructive shear testing and cross-sectional analysis. A scanning electron microscope was used to inspect and examine the bonded joint quality. Finally, completed assemblies were thermal cycled to evaluate degradation of joint strength under induced stress, and resistance measurements were performed to evaluate the electrical performance of the bonded copper joint.

Experimental Investigation on the Effect of Nickel-plating Thickness on Continuous-wave Laser Welding of Copper and Steel Tab Joints for Battery Manufacturing

The welding of dissimilar materials, such as copper and steel, holds significant industrial significance in the production of electric vehicle batteries. These materials are commonly used in the case of connections between busbars and cylindrical cells inside a battery pack. To optimize welding and guarantee protection against corrosion, nickel is commonly used in the form of a coating. In this paper, the effect of nickel plating thickness on copper-to-steel welds made with laser technology is investigated. The initial phase consists of a statistical characterization of the nickel plating thickness of the busbar in order to identify the thickness ranges. Experiments were conducted using two different fiber laser sources (a single-mode laser source and a beam-shaping laser source) equipped with a Galvo scanner head; the fluence value and the thickness of nickel plating varied during the experiments. The study conducted has revealed that the thickness of nickel plating plays a crucial role in the weld bead interface, particularly when using a single-mode source. Furthermore, when using the beam-shaping laser source, the fluence employed can have a significant impact on both the depth of penetration and the interface width.

Effect of Different Step-Lap Joints on the Natural Frequencies of Different Adhesively Bonded Metallic Materials: A Numerical Study

Due to their many applications' benefits, adhesively bonded joints are widely utilized in nearly every industry, including space, marine, automotive, and aeronautics. Since unpredicted loadings may cause resonance in the structures, an accurate prediction of the bonded joints' dynamic characteristics is crucial. Therefore, in this study, modal analysis was performed on the two-, three-, four- and double-step adhesively bonded lap joints of Aluminum (Al), Copper (Cu), and Mild steel (Ms) materials with Epoxy Araldite adhesive. Ansys commercial program was utilized to analyze it numerically. The results showed that modeling the bonding region of single lap joints as two-, three-, and four-step adhesively bonded lap joints has no significant effect on the natural frequencies. This modeling has a minor incremental effect on the natural frequencies. However, Double-step lap joints were found to cause a considerable reduction in natural frequencies compared to not only single lap joints but also two-, three-, and four-step adhesively bonded lap joints. Double-step bonding caused a decrease of 8.82%, 8.57%, and 8.73% for Al-Al, Cu-Cu, and Ms-Ms. In general, in all models, the best increase or decrease in terms of natural frequencies was found to be Cu-Cu adhesively lap joints.

Tool Rotational and Tool Travel Parameters Influence On Friction Stir Welded Dissimilar Joints Properties

Present work is to examine the effects of tool rotational and tool travel parameters on Friction Stir Welded (FSW) dissimilar joints mechanical and microstructural characteristics for 3 mm thick pure copper and 6061 aluminium alloy plates. Welds were made with a cylindrical tapered pin to achieve this goal. The tool rotational speed and tool travel speed are the primary FSW factors considered in this study. Copper plates were kept on the joint's advancing side. Tensile and bending tests are carried out to assess the tensile and bending strength of weld joints in accordance with ASTM standards. Vicker's microhardness tests were carried out in the transverse direction of the weld to check the hardness distribution in weld nuggets. An experimental analysis shows that the best tensile strength 98 MPa and bending stress 16.6 MPa are achieved at tool rotating speeds of 1000 rpm and 62 mm/min, correspondingly. The larger concentration of copper particles in the aluminium region is mostly to blame for this. For 1400 rpm and 62 mm/min, a nugget zone hardness of 190 HV is attained. The presence of more Cu particles on the Al side is evident in SEM pictures, and the higher tensile and bending strength is mostly attributable to the Cu particles covering the Al material in the weld zone. According to X-ray analysis, the synthesis of intermetallic complexes such Al4Cu9, Al2Cu, AlCu, and AlCu4 explains the chemical reaction and phase transformation at the interfaces. The maximum strength values improved because of these intermetallic compounds' proper metallurgical bonding and thinnest thickness. According to fracture analysis, joints with higher strengths have intergranular fracture, while joints with lower strengths experience brittle fracture on both aluminium and copper joints.

Cooling-assist friction stir welding: A case study on AA6068 aluminum alloy and copper joint

This study evaluates the impact of cooling-assist friction stir welding (CA-FSW) tool rotational and traverse velocities on the bonding quality of Al-Cu-Mg and copper lap joints. A modified computational fluid dynamics (CFD) technique analyzes heat generation and distribution during dissimilar CA-FSW joints between AA6068 alloy and copper. The relationship between CA-FSW tool velocities and metallurgical properties of the final joint is assessed. Simulation results provide insights into metallurgical phenomena during the CA-FSW process. Findings reveal greater plastic deformation and heat generation on the AA6068 aluminum alloy side due to raw material placement, resulting in more significant microstructure changes in AA6068 aluminum alloy compared to copper. Increased heat generation leads to higher copper-rich intermetallic compound (IMC) formation, resulting in increased hardness of the stir zone at the base metals’ interface.

Evaluation of ultrasonic spot welded Al-Cu dissimilar sheets: Mechanical performance, microstructural changes and thermal analysis

Automotive lithium-ion battery manufacturing industries are increasingly using ultrasonic welding (USW) to join thin dissimilar metals and foils. USW has good joint efficiency, no formation of the heat-affected zone, high production rate, shorter welding time, and sustainability over conventional fusion welding techniques. However, this process is less distinct and precise control of weld surface conditions to get good quality welds. In this regard, experimental and thermal analysis significantly helps to control the state of the weld interface during the joining process. In this study, the objective is to enhance the mechanical performance of aluminum (Al) and copper (Cu) joints under different surface conditions such as lubricating, normal, electrolytically, and emery polished. According to the lap shear tensile load result, the joint strength decreases significantly with the rise in weld time after 0.7 s. The lubricating surface provides the maximum lap shear tensile load of 1507 N among all other surface conditions. Fracture surface analyses are conducted to determine the quality of welds under varying surface conditions. Additionally, a three-dimensional (3D) finite element model (FE) for ultrasonic welding of two highly conductive metal sheets is also being investigated for the purposes of analysing the thermal behaviour around the weld interface. It reveals that the thermal profile of the interface differs depending on the surface condition. The numerical framework is confirmed by comparing the predicted interface temperature variations at different faying surface conditions with the experimental results.

Deep Convolutional Neural Network Algorithm for Prediction of the Mechanical Properties of Friction Stir Welded Copper Joints from its Microstructures

Convolutional Neural Network (CNN) is a special type of Artificial Neural Network which takes input in the form of an image. Like Artificial Neural Network they consist of weights that are estimated during training, neurons (activation functions), and an objective (loss function). CNN is finding various applications in image recognition, semantic segmentation, object detection, and localization. The present work deals with the prediction of the welding efficiency of the Friction Stir Welded joints on the basis of microstructure images by carrying out training on 3000 microstructure images and further testing on 300 microstructure images. The obtained results showed an accuracy of 80 % on the validation dataset.

Tensile and microstructural behavior of gas-tungsten-arc-welded electrolytic tough pitch copper joints

Electrolytic tough pitch (ETP) copper is extensively used in the manufacturing of electrical machines and automobiles. Compared with other pure coppers, ETP copper has lower weldability. Therefore, this study analyzes the weldability of ETP copper using the gas tungsten arc welding (GTAW) process. GTAW can be performed using constant-current (CC) and pulsed-current (PC) modes. Consequently, the properties of the joints fabricated using both modes are compared and analyzed in this study. The results show that the joint efficiencies of GTAW-CC and GTAW-PC joints are 81 and 89%, respectively. The optimal heat input and pulsating action in PC mode produce refined grains in the weld zone and heat-affected zone, resulting in a higher joint efficiency.

Microstructures and Electrical Resistivity of Aluminum–Copper Joints

Using pulsed double electrode-gas metal arc welding, aluminum wires are joined to copper plates with fillers of different fractions of silicon. Two layers of different microstructures are formed near the Al-Cu interface: one consists of a hypoeutectic microstructure of α (Al) + Al2Cu, and the other consists of an intermetallic compound (IMC) of Al2Cu. Increasing the heat input causes increases in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. Si suppresses the growth of the IMC layer and assists the growth of the layer of the hypoeutectic microstructure. The effects of the interface microstructures and chemical compositions on the electric resistivity of the joints are analyzed. The electric resistivity of the joints increases with the increase in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. The law of mixture is used to calculate the electric resistivity of the joints, which is in accordance with the experimental results.

Parametric optimization of AA6061-Cu friction stir welded joints with boron carbide particle reinforcement

ABSTRACT The objective of this work is to improve the mechanical properties of friction stir welded square butt joints of AA6061 and pure copper employing activated flux of B4C micro powder. Rotational speed, transverse feed and tool penetration depth were optimized using Taguchi method to produce joints devoid of defects. Rotational speed was found to be the most influential process parameter in achieving the higher ultimate tensile strength and has 49% contribution followed by feed and penetration depth. Model predictions for the optimal strength were validated and found to have 5 % variation. Highest ultimate tensile strength and micro Vickers hardness of 259.57 MPa and 98.58 HV respectively were obtained for joints made with speed, feed and penetration depth of 1250 rpm, 20 mm/min and 0.1 mm respectively. The microstructural analysis revealed that B4C particles were distributed uniformly in the stir zone which could be the reason for improved mechanical properties.