TEM analysis and molecular dynamics simulation of graphene coated Al-Cu micro joints

This study compares friction-stir spot welds (FSSW) of pure Al to Cu, with and without graphene interlayer (GL), for tensile load and electrical conductivity (σ). The weld interface of Al-Cu fabricated without a GL is found with brittle intermetallic compounds (IMC) like Al2Cu. The presence of brittle IMCs significantly affects the tensile load and σ. In contrast, the sample with GL suppresses the brittle IMCs and enhances the formation of Al4C3 IMC. The presence of Al4C3 strengthens the weld joint by 26.94 % concerning the without GL samples. Further, it was observed that thinner and high-density twins are formed in the samples with GL. The formation of thinner deformation twins is also possible for increased tensile load and σ. The thicker twins in the samples without GL inhibit the electron flow and increase electrical resistivity. The molecular dynamics (MD) simulation was performed to study the in-situ formation of deformed twins. In addition, the MD simulation provides insight into the influence of graphene during the formation of IMCs based on diffusion coefficients of individual atoms. The σ of the Al-Cu joint can be estimated using a cluster Nernst-Einstein equation, which is dependent on the diffusion coefficient obtained from MD simulation

An investigation of mechanical and electrical properties of friction stir welded Al and Cu busbar for battery pack applications

The aluminum and copper (Al–Cu) busbar is widely used as a core component in Lithium-Ion (Li-ion) batteries. The Al–Cu busbar is challenging to fabricate with the traditional welding processes because of its high thermal conductivity. The Al–Cu busbar is fabricated using the friction stir welding method in the present study. The effect of temperature and vibration generated during the welding process on intermetallic compounds (IMCs) is studied using the effective formation model and found that Al2Cu is the first to form at the interface. The IMC formation at the joint interface had detrimental (Al-rich IMC) and beneficial (Cu-rich IMC) effects. The presence of detrimental IMCs affects the joint strength of about 36% as compared to the sample with the highest tensile load. The surface electrical conductivity is measured by using a Gaussian profile method and found in the range of 0.94–5.37 μ Ω·mm. The welded samples with the presence of Al2Cu3 and Al4Cu9 IMC at the interface are found to have higher electrical conductivity. Interestingly, the sample with a higher tensile load had observed higher electrical conductivity due to the formation of Cu-rich IMC, i.e., Al4Cu9

Effect of weld parameters on joint quality in friction stir welding of Mg 2 alloy to DP steel dissimilar materials

Dissimilar material joining between magnesium (AZ31B) alloy and dual-phase steel (DP600) was achieved using the friction stir welding (FSW) process. The present work aimed at studying the effect of tool rotational speed and welding speed on the microstructure and mechanical properties of the dissimilar joints. The joints were fabricated at tool rotational speeds of 800 and 1600 rpm with weld speeds of 50, 100, and 150 mm/min, respectively. The plunge depth of 0.2 mm and tool tilt angle of 2° was kept constant during the welding. Temperature rise and variation of torque during the welding process were recorded. Optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy (EDS), and X-ray diffraction studies were carried out to understand the microstructural changes, the interface of the weld joints, fracture morphology, and formation of intermetallic compounds during FSW. Maximum joint efficiency of 76.4% was achieved with respect to AZ31B. The microstructural observation revealed the formation of finer grains at the stir zone for all weld parameters because of the dynamic recrystallization. The metallurgical bonding between the dissimilar materials was observed due to the formation of intermetallic compounds. The formation of the sawtooth profile at the joint interface indicated mechanical interlocking between AZ31B Mg alloy and DP600 steel. Though the AZ31B Mg–DP600 steel combination is highly immiscible, the present attempts have successfully created the joining, where one of the substrates provides lightweight while the other provides strength

Characterization and modelling of Al and Cu busbar during charging and discharging of Li-ion battery for electric vehicles

The electrical components such as bimetallic busbar joints of the lithium-ion (Li-ion) batteries should be able to withstand high voltages during charge and discharge processes. The busbar is an essential component that transmits high power to electrify the vehicle. The present study describes the sustainability of friction stir welded (FSW) busbar at different C-rates by simulating a Li-ion battery attached to a busbar, then correlating the heat generation of simulation results with an experimental result at 1, 1.5, and 2C-rates. The change in process parameters of FSW samples varies with electrical conductivity at the weld interface. The variation in electrical conductivity with different busbars is due to the formation of various intermetallic and changes in the grain size of the Al and Cu joints. However, the busbar with Cu-rich intermetallic exhibits smaller electrical resistivity. The specific electrical contact resistance of a busbar is obtained from simulation by validating the heat generated during constant time charge–discharge cycles. The temperature rises due to contact resistance in the Al-Cu busbar which can lead to thermal runaway and, eventually, short circuits in the Li-ion battery pack. Based on previous simulation parameters, the Li-ion cells are simulated at 5 and 10C-rates to understand thermal runaway behaviour

Molecular dynamics simulation of atomic diffusion in friction stir spot welded Al to Cu joints

Dissimilar metals joining, especially Aluminum (Al) to copper (Cu), have gained importance in batteries for electric vehicles. Although friction stir spot welding (FSSW) has recently been used for welding dissimilar materials, progress has been very slow toward understanding the effect of temperature on diffusion condition between the two materials with the same FCC crystal structure. The thermo-mechanical modeling has been used to define the trajectory of Al and Cu particles at the weld interface, but it had a limitation to quantified the diffusion coefficient. Hence, the molecular dynamics (MD) study has been used to investigate the atomic interdiffusion of Al and Cu. The transmission electron microscopy results are used to validate the MD simulation outcome to understand the formation of dislocations and intermetallic compounds. The MD results implicated the formation of γ-phase (BCC), i.e., Al4Cu9 IMC toward the Cu side. Further, the In-situ investigation of non-FCC phase formation at FSSW condition has also been studied

Modelling and experimental study of laser-assisted milling of fibre reinforced SiC/Ti-6Al-4V metal matrix composite

Metal matrix composites (MMCs) offer unique advantageous mechanical properties by strengthening a ductile metal matrix with a ceramic reinforcement (e.g., Ti6Al-4 V/SiCf). However, their heterogeneous composition poses machining challenges including fibre pullout, matrix cracking, and increased tool wear. Whilst pre-heating via laser-assisted machining (LAM) shows promise for improving machinability, traditional LAM implementations with a fixed laser spot size and straight laser path prevent uniform heating. By introducing spatially and temporally controlled LAM that generates homogeneous heating by varying the laser scanning velocity, a technique called fully inverse LAM can be applied for MMCs. This involves calculating separate temperature fields for the matrix and reinforcement to minimise thermal mismatch stresses. The fully inverse LAM decreases subsurface cracks and delamination resulting from conventional milling, whilst localised matrix softening reduces cutting forces by over 62 %. Flank tool wear is also diminished, increasing tool life by 120 %. Material analysis reveals reduced machined surface damage, lower surface roughness, and less formation of intermetallic compounds (Ti2C) compared to traditional LAM

Machining SiC fibre reinforced metal matrix composites – How do different matrix materials affect the cutting performance?

SiC fibre reinforced metal matrix composites find widespread application but show major machining difficulties due to significant variations in constituents' properties. In this sense, while the SiC fibre plays significant strengthening effects, the properties mismatch between the brittle fibre and ductile matrix materials becomes important in their machining performance. Through machining tests, SiC fibre reinforced MMCs with Al (soft) and Ti (hard) matrix alloys are evaluated, showing the variation of interaction between inserts and fibres in cutting due to the different matrix properties. This leads to less tool wear but compromised surface integrity in Al-based composite than in Ti-based one

The synthesis of novel porous graphene anodes for fast charging and improved electrochemical performance for lithium-ion batteries

As part of sustainable development goals seven and thirteen, electric vehicles (EV) are taking over internal combustion engine vehicles by using battery packs as their power source. One major concern for the EV sector is the charging time of lithium-ion (Li-ion) batteries. Advancing the battery pack industry and the EV sector will benefit economically and environmentally by creating pores on the graphene anode using the NaCl activation method, eventually leading to high performance and efficiency in Li-ion batteries. Accordingly, the present study focused on fabricating novel macroporous graphene (MPG) anodes for fast-charging Li-ion batteries. Macropores increase the anode surface area, thereby enhancing lithiation. The performance of the novel MPG anode is compared with that of the commercial mesocarbon microbead (MCMB) anode. As a result, the MPG anode exhibits a 15% faster charge than the MCMB at a 0.1 C rate. Moreover, the specific capacity of the MPG anode retains 16.3% higher than the MCMB anode after the completion of the 100th cycle