Enhanced Mechanical Properties in 6082 Aluminum Alloy Processed by Cyclic Deformation

Aging heat treatment is the most commonly used strengthening method for Al–Mg–Si alloys since high-density precipitates will be formed to hinder the movement of dislocations. In the current work, room temperature cyclic deformation was attempted to strengthen the alloy. We compared tensile test results of aged samples and cyclically deformed samples. It was found that cyclically deformed samples can achieve similar strength and approximately twice the uniform elongation as the peak aged samples. The high density of dislocations and nanoclusters observed in the cyclically deformed samples is thought to be the main reason for strengthening. Different cyclic deformation conditions have been tried and their effects were discussed.

Effects of Aging on the Microstructure and Phase Transformation Behavior of Cu-Al-Mn Shape Memory Alloy

In the present work, the effects of artificial aging treatment on the transformation temperatures and hardness of Cu-Al-Mn shape memory alloy have been investigated. The aging processes have been performed on the one-time re-melted and 90% rolled samples. Differential scanning calorimetry reveals that reverse transformation is present for the re-melted sample which is aged at 400°C. However, in 90% rolled condition, this transformation takes place at 200°C and 300°C. Hardness examination shows that the aged specimens possess higher values in hardness in comparison to un-aged samples at all studied temperatures. Although, the peak-aged condition was demonstrated at 300°C for the re-melted sample, the rolled sample displayed increased hardness levels up to 500°C. Based on the DSC measurements and microstructural observations, it can be asserted that the thermo-mechanical processing including rolling plus aging at 300°C provides favorable transformation characteristics for shape memory behavior.

Dynamic ESPI Evaluation of Deformation and Fracture Mechanism of 7075 Aluminum Alloy

The deformation and fracture mechanism in 7075 aluminum alloy is discussed based on a field theoretical approach. A pair of peak-aged and overaged plate specimens are prepared under the respective precipitation conditions, and their plastic deformation behaviors are visualized with two-dimensional electronic speckle pattern interferometry (ESPI). The in-plane velocity field caused by monotonic tensile loading is monitored continuously via the contour analysis method of ESPI. In the plastic regime, the peak-aged specimen exhibits a macroscopically uniform deformation behavior, while the annealed specimen exhibits non-uniform deformation characterized by a localized shear band. The occurrence of the shear band is explained by the transition of the material’s elastic resistive mechanism from the longitudinal force dominant to shear force dominant mode. The shear force is interpreted as the frictional force that drives mobile dislocations along the shear band. The dynamic behavior of the shear band is explained as representing the motion of a solitary wave. The observed decrease in the solitary wave’s velocity is accounted for by the change in the acoustic impedance with the advancement of plastic deformation.

Self-Piercing Riveting of Medium- and High-Strength Al and Mg Alloy Sheets Enabled by In-Process Electric Resistance Heating

Enduring joints of high-strength materials are becoming increasingly important for the manufacturing of highly loaded body-in-white structures, particularly for automobiles, which require structural light-weighting without sacrificing passenger safety. While self-piercing riveting has been proven suitable for various material classes, its application to high-strength, low-ductile materials is hindered by the occurrence of cracks and insufficient penetration. In this work, we demonstrated that these restrictions can be overcome by localized one-sided short-time electric resistance heating. The treatment can be integrated into the riveting process, allowing for short process times. The heating lowers the hardness of the materials to be joined and enables piercing and penetration of the sheets to yield crack-free joints. The local mechanical properties are hardly changed in case of peak-aged sheet material conditions but increase significantly in the close vicinity of the rivet in case of under-aged sheet material conditions. The outstanding static and dynamic mechanical properties of the resulting joints evidence their robustness.

Excellent age hardenability with the controllable microstructure of AXW100 magnesium sheet alloy

Age-hardenability and corresponding improvement of the mechanical properties of Mg–1Al–0.7Ca and Mg–1Al–0.7Ca–0.7Y alloy sheets are addressed with respect to the microstructure and texture evolution during thermomechanical treatments. A fine grain structure and weak texture with the basal pole split into the sheet transverse direction are retained in the Mg–1Al–0.7Ca–0.7Y sheet even after the homogenization at 500 °C, due to the grain boundary pinning by Y-containing precipitates possessing a high thermal stability. Contrarily, the Mg–1Al–0.7Ca sheet shows a coarse microstructure and basal-type texture after the homogenization. The peak-aged condition is attained after the aging at 250 °C for 1800 s of both homogenized sheets, while the Y-containing sheet shows a higher hardness than the Mg–1Al–0.7Ca sheet. TEM analysis and thermodynamic calculation show the formation of metastable precipitates composed of Al, Ca, Y and Mg in the Mg–1Al–0.7Ca–0.7Y sheet at the homogenized and peak-aged conditions. A significant increase in the yield strength is obtained in the peak-aged condition from 162 MPa after the homogenization to 244 MPa, which arises from the increased size and number density of the precipitates. The high age-hardenability of the Mg–1Al–0.7Ca–0.7Y sheet attributes to the superior mechanical properties with an improved ductility promoted by the weak texture.