Mohammad Bakhshi-Jooybari

Today, an increasing demand for the lightweight materials in automotive, aircraft, railway, and marine industries has led to an increase in utilization of materials such as composites, aluminum alloys, copper, high-strength steel, and magnesium alloys. In this context, new methods called solid-state joining have been developed to join metals effectively. Among these methods, electromagnetic joining stands out for its cost-efficiency and high speed. This research investigates the effect of voltage parameter on mechanical properties, hardness, and microstructure of the composite joints to copper using electromagnetic bonding method. The results indicated that as the voltage increases, the bond between the two tubes becomes stronger, with the joining force reaching 2.3 kN at a voltage of 8 kV. At voltage of 8 kV, due to an increase in the impact velocity, more severe plastic deformation occurs in the specimen, compared to those in the other specimens. This causes an increase in the hardness of the specimen which was about 8% higher than that of the 5 kV specimen. Furthermore, microstructural examination revealed that with an increase in voltage, a continuous joining was created between the two tubes and there was no gap between the two surfaces, resulted in sufficient strength of the joining.

High-temperature forming is a conventional method for improving the formability of metals, but it involves high costs and long processing times. As an alternative, this study investigates the electroplastic effect (EPE) on the formability of annealed AA6061 aluminum alloy under different stress states. Hydraulic bulge tests were performed on circular and oval notch specimens, both with the application of electric current at appropriate current parameters and without the application of electric current. The results show that applying electric current at appropriate current parameters increased the equivalent plastic strain at fracture by 3.92% and 5.55% in circular and oval notch specimens, respectively. Dome height increased, fracture pressure decreased, and dome thickness was reduced, all indicating enhanced formability. The effectiveness of the EPE was found to decrease with increasing stress triaxiality. These findings confirm that electric current-assisted forming can improve ductile fracture behavior in AA6061 under complex loading conditions, offering potential for industrial applications.

The technology of using electric current in metal forming processes is an innovative technology. The utilization of current in these processes has diverse consequences on the plastic behavior of distinct alloys. This study examines the electroplastic effects on the plastic behavior of AA6061 aluminum alloy sheets subjected to two distinct heat treatment conditions: T6 and annealing. The study employs uniaxial tensile testing to examine these effects. The appropriate current parameters were first determined from a set of parameters. By applying electric current at appropriate current parameter conditions during uniaxial tensile test, the formability of the samples increases, which it is more pronounced in the annealed condition. In the T6 condition, applying electric current at appropriate current parameters results in 5.7% increase in formability, 3.11% increase in ultimate strength, and 3.79% increase in yield stress. while in the annealed condition. This leads to an increase of 23.4%, no change in ultimate strength, and 20.71% increase in yield stress. By qualitative analysis of the microstructure using scanning electron microscope (SEM) images of the fracture surface, it was observed that this phenomenon can be attributed to an augmentation in the size and number of fracture surface dimples in the annealed condition, compared to T6 condition. Furthermore, the application of electric current with the appropriate parameters in the annealed sample intensifies the size and number of the dimples and increase in the formability.

An accurate material model significantly improves the simulation accuracy of tube hydroforming processes. To precisely calibrate a ductile fracture criterion, it is necessary to conduct fracture experiments that encompass a broad spectrum of stress conditions. Furthermore, a more accurate calibration is achieved when applying tube geometry-based tests, which present a more exact reflection of process conditions. Comprehensive phenomenological criteria with a wide coverage of stress states have not been used in the tube hydroforming process. Moreover, the need for a comprehensive calibration process based on tube geometry has not been underlined due to the simplicity of the considered criteria. This research provides a novel environment where innovative fracture experiments with nested tubes are designed and performed in a single setup. Certain cut-outs with special geometries are designed on the outer AA6063-T6 tube, considered for fracture. The inner tube, made of ductile metal, acts as a medium to transfer hydraulic pressure to the outer tube. Iterative finite element simulation was applied to design the geometry of cut-outs on the outer tube. The modified Mohr-Coulomb criterion (MMC3) is calibrated using these fracture experiments. A comparison between the experimental and simulation results showed the efficiency of the fracture criterion calibrated by the proposed tests, where the pressure, bulge height, and tube thickness at fracture onset were predicted with average errors of less than 13%, 9%, and 3%, respectively.

The present work focused on the effect of the electric current pulse type on the springback, microstructure, texture, and mechanical properties during the V-bending process of AA2024 aluminum alloy. In order to investigate this effect, three different forming conditions including conventional V-bending and electrically assisted V-bending with square and sinusoidal pulses were considered. The results indicated that the amount of springback significantly decreased from 45.5 deg (for the sample formed via conventional V-bending) to 24 deg by applying the sinusoidal pulse. Microstructural observations revealed lower stored energy in the samples formed by electric current pulses which resulted in larger grain size compared with the samples formed without electric pulses. In addition, the result showed that the intensity of the 〈111〉||BLD (bend line direction) fiber texture reduced after applying electric current pulses, whereas it was very strong in the sample formed without electric pulses. It was suggested that the electric current pulses led to change the slip plane of the dislocations from {111} to {110} through cross slip. The applying electric current pulses decrease the ultimate tensile strength (UTS) from 471.1 MPa (for the conventional tensile test) to 448.0 and 426.7 MPa for the square and sinusoidal pulses, respectively. On the other hand, the electric pulses improved the formability of the AA2024 alloy owing to the activation of more slip systems, inhibition of dislocation pinning, the promotion of dislocation movement, and the acceleration of restoration mechanisms.