Effect of Residual Aluminum Thickness on Microstructure and Strength of Friction Stir Spot Welded Aluminum Alloy/Copper Lap Joint

Dissimilar metal lap joining of A5052 aluminum alloy plate and C1100 pure copper plate was performed by using friction stir spot welding. The rotating welding tool, which was composed of a probe part and a shoulder part, was plunged from the aluminum alloy plate which was overlapped on the copper plate, and residual aluminum alloy thickness under the probe part of the welding tool after plunging of the welding tool was controlled in the range from 0 mm to 0.4 mm. The strength of the welding interface was evaluated by using tensile-shear test. Microstructure of the welding interface was examined by using an optical microscope and a field emission scanning electron microscope. The welding was achieved at the residual aluminum alloy thickness under the probe part of the welding tool below 0.3 mm. The welded area was formed at aluminum alloy/copper interface located under the probe part of the welding tool, and its width increased with decreasing the residual aluminum alloy thickness. A characteristic laminate structure was produced in the copper matrix near the welding interface. In the joint fabricated at the residual aluminum alloy thickness below 0.1 mm, hook of Cu was formed at edge of the welded area. The fracture did not occur at the welding interface. A remarkable improvement in strength was observed in the joint fabricated at the residual aluminum alloy thickness below 0.1 mm. The formation of laminate structure and hook is considered to result in joint strength improvement.

Implementation of Laminate Structure in Car Hood and Study of its NVH Parameters

This paper examines the implementation of Laminate structure and aluminium panels in Hood in place of conventional steel hood. In laminate structure, 3 layers is considered with aluminum as a face material and PVC Solid as a core material which helps in efficient energy absorption and provide necessary stiffness for the panel. It has been observed that the natural frequency is improved over conventional steel bonnets with benefit of weight reduction in hood assembly. To validate its NVH performance static stiffness, natural frequency and torsional stiffness has been calculated and it has been found that Laminate structure Hood has better performance than steel hood with overall weight reduction of 41.36%.

Structural Design and Mechanical Performance Analysis of Carbon Fiber Closed Fixtures for UHV Transmission Lines

The closed clamp is a standard tool for the insulator replacement in ultrahigh voltage (UHV) transmission lines, which is mainly made of titanium alloy material and weighs more than 27 kg that greatly reduces the working efficiency for operators. Due to the lightweight demand, carbon fiber composite materials are applied to design a new type of clamp, in which mechanical properties of new fixtures need to be fulfilled while considering poor impact resistance and low interlaminar shear strength of carbon fiber composite materials. To excavate a high-strength ply structure, finite element progressive damage strength analysis is employed to evaluate the mechanical properties of three different ply angles of the carbon fiber closed fixture, in which Tsai–Wu strength theory is thought as the strength judgment basis for carbon fiber composite materials. After comparison with the displacement-load curves, the three different ply angles fail to meet the strength requirements. So, a carbon fiber laminate structure with an outer cladding for carbon fiber closed fixtures is raised and verified. The analysis results show that the laminate structure meets the strength requirements. Destructive test of the new closed clamp is conducted to verify the correctness of the proposed method, and the weight is reduced by 36.46%.

Strain Hardening Behavior of Laminate Structure With Stable bcc/fcc Bimetal Interfaces

This work developed a well-bonded bcc/fcc bimetal interphase, which was produced by a two-step process involving diffusion bonding and conventional rolling. The high-quality interface maintained its integrity even at fracture. The earlier tensile instability in the core steel layer was constrained by the neighboring stable Cu layers on both sides, leading to extra strain hardening and consequently higher ductility. An increase in twin density or slip bands and shear deformation between the layers might be the primary causes for the observed hardening behaviors in the near-interface regions.

Tensile Deformation Behavior of Typical Porous Laminate Structure at Different Temperatures

In this study, the Ni-Cr-W superalloy GH3230 is used as the test material. According to the actual structure of the flame tube, a porous laminate structure specimen is designed. The structure consists of impact holes, overflow holes and pin fins. High-temperature tensile tests at 650 °C, 750 °C and 850 °C were carried out to study the high-temperature mechanical properties and fracture mechanism of the specimens of porous laminate structure, and the strain nephogram of the specimens were obtained by digital image correlation (DIC) technique. Due to the large number and dense arrangement of overflow holes, an obvious hole interference effect can be found from the strain nephogram. The stress concentration around the pore and the interference between the pores provide priority places and paths for the initiation and propagation of microcracks. The test found that the microcracks of the porous laminate structure first occurred around the hole, the overflow surface fractured first, after which the impact surface fractured. The strength of the alloy exhibits a significant temperature sensitivity to temperature. From 650 °C to 750 °C, the ultimate strength (σb) and yield strength (σ0.2) decrease slightly, but they decrease significantly at 850 °C. The microstructure of the fracture surface shows that all microcracks occur at the interface between the matrix and the carbides but that the fracture mode of the specimens gradually changes from intergranular fracture to transgranular fracture as the temperature increases. Due to the pinning effect of the intracrystalline diffusive solute atoms on the dislocations, the stress-strain curves of the high-temperature tensile tests at 650 °C and 750 °C showed zigzag characteristic fluctuations during the strengthening stage.