Friction stir processing is an important method for acquiring ultrafine-grained materials. In this paper, 3mm ZK60 magnesium alloy sheet was carried for friction stir processing. The best processing parameters with a small grain size and maximum mechanical properties were obtained by comparing different rotation speeds and processing speeds. Fine recrystallized grains and high-angle grain boundaries were observed in stirring zone under different processing parameters. With increasing rotation speed, the grain size and high-angle grain boundary ratio increase; while with increasing processing speed, the grain size decrease, and the ratio of high-angle grain boundaries increase. When rotation speed and processing speed are 1400 r·min-1 and 100 mm·min-1, the processing plate have the largest ultimate tensile strength are 267.52 Mpa, that reached 84.62% of the base metals, and the yield strength, elongation and grain size are 166.97 Mpa, 15.32 % and 1.12 ± 1.64 µm, respectively. The processing plate has more excellent damping performance than rolled.
Investigations of composite based on a spray deposition Al-Zn-Mg-Cu alloy reinforced with SiC particles with the volume fraction of 15% and various extrusion ratios of 11-39 are presented. Bars with a diameter of 8-15 mm were obtained as the end product. Based on the microstructural examinations of the composite, we can find that SiC particles adhered mainly to the surface of the alloy droplets during deposition, leading to more SiC particles at the surface of the droplets and less in the inner. Thus, the distribution of SiC particles in the billet was characteristic of the layered feature. This layered feature of SiC particles was not completely removed by the following hot extrusion. The SiC particles were distributed like the streamline in the longitudinal direction. A higher extrusion ratio resulted in an more uniform distribution of SiC particles. Ambient tensile tests made it possible to demonstrate that the mechanical properties improve with the increasing of extrusion ratio. The ultimate tensile strength and elongation achieve 475 MPa and 16.5% at an extrusion ratio of 39.
High strain rate rolling (HRSS) of a ZK60 magnesium alloy at 300 °C with a strain rate from 5 s−1 to 25 s−1 was used to research the effect of the rate on the mechanical properties and damping capacity of the ZK60 alloy. The results show that as the strain rate increases, the tensile strength decreases from 355 MPa at 25 s−1 to 310 MPa at 5 s−1. Two damping peaks (P1 and P2) are detected in the high strain rate rolled ZK60 alloys at different strain rates. The P1 peak appears at low temperatures and is caused by grain boundaries sliding. The P2 peak appears at high temperatures and is caused by recrystallization. As the strain rate increases from 5 to 20 s−1, the dynamic recrystallization (DRX) volume percent rises and the dislocation density decreases, both of which cause the P1 peak to become more and more obvious, and activation energy rises. At the same time, the dislocation density decreases and leads to a decrease in the storage energy, which reduces the recrystallization driving force and shifts the P2 peak to high temperatures. When the strain rate reaches 20 and 25 s−1, DRX occurs fully in the sheet, so the activation energy of the P1 peak and the temperature where the P2 peak appears are basically equal.
The aluminium alloy front subframe of an automobile was developed through multi-operating condition topology optimization and multi-objective optimization methods. By considering the influences of loads on the strength, static stiffness, and modal of the aluminium alloy front subframe under typical operating conditions, the performance parameters of the aluminium alloy front subframe after topology optimization were obtained. After topology optimization was performed, the parametric model of the aluminium alloy front subframe was established. Based on the Isight optimization platform, sample points were generated with the optimal Latin hypercube test method, and the response surface approximate model was constructed. The minimum mass and maximum first-order frequency were taken as the objectives, the stress under typical working conditions did not exceed the set target value, and the maximum displacement of the installation point was taken as the constraint condition. The multi-objective particle swarm optimization algorithm was used to optimize the aluminium alloy front subframe. The error of the free modal and finite element free modal analysis of the aluminium alloy front subframe samples was less than 15%. The optimized aluminium alloy front subframe was 2.4 kg lighter than the original subframe under the premise of satisfying various performance indices, and the lightweight rate was up to 12%.
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