Papers by Author: Yong Bo Xu

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Authors: B.J. Duggan, G.J. Shen, Yong Bo Xu
Authors: Gui Ying Sha, Yong Bo Xu, En Hou Han
Abstract: The dynamic experiments for the Mg-Li alloys with single phase structure were carried out using the Hopkinson pressure bar. The dynamic crack propagation behavior and fracture mechanism of the alloys were investigated. The results show that the dynamic crack propagation is a deceleration process for the Mg-Li alloys under high loading rate. The fastest crack propagation velocity for Mg-3.3Li alloy is m/s 37 . 1253 , and 935.36m/s for Mg-14Li alloy. Observations of the fracture by SEM reveal that the dynamic fracture surface for Mg-3.3Li alloy mainly appears to be brittle fracture along grain boundaries. Whereas, the Mg-14Li alloy is ductile fracture mode under high loading rate. The main reason for these may be the transformation of hcp→bcc structure and the precipitation of the MgLi2Al and AlLi, as increase of Li in Mg-Li alloy.
Authors: Gui Ying Sha, En Hou Han, Yong Bo Xu, Lu Liu
Abstract: The dynamic stress-strain behavior of the AZ91 alloys in different treatment conditions (as-cast, T4 and T6) was investigated by means of split Hopkinson pressure bar. It was found that the flow stress increased at first, and then declined with the strain rate increasing at the range of 102~103s-1 for the alloys in these three conditions. And the alloys exhibited both positive and negative strain rate effects. The former was caused by strain rate strengthening and the latter was caused by strain rate weakening. However the flow stress for the alloy in aged condition at the same strain rate was higher than both of the alloys in as-cast and solution conditions. The study also showed that the maximum strains of the alloys in different conditions increased with the strain rate increasing, and the strain rate to fracture for the alloy in solution condition was higher than those of other two alloys. The work-hardening of α–Mg matrix and the reinforcement of β-Mg17Al12 phases led to the strengthening of the alloy, while thermal softening of matrix, the fracture of β phases and initiation and propagation of the cracks were responsible for the weakening of the alloy.
Authors: T. Liu, Yan Dong Wang, Shi Ding Wu, Shou Xin Li, Ru Lin Peng, Yong Bo Xu
Abstract: The room temperature tensile strength and ductility of Mg-3.3%Li alloy were improved simultaneously by two kinds of different equal channel angular pressing (ECAP) treatments. Microstructural analyses showed that grain refinement and texture modification are the principal reasons for the improvement of mechanical properties.
Authors: Dao Kui Xu, Wei Neng Tang, Lu Liu, Yong Bo Xu, En Hou Han
Abstract: In this paper, the fatigue crack propagation (FCP) behaviors of the forged Mg-Zn-Y-Zr alloy with different tempers were investigated. At the stage 1 of the FCP, the  K-da/dN curves were distinguished from each other. However, at the stage 2 of the FCP, the  K-da/dN curves were almost the same. SEM fracture analysis indicated that at the stage 2 of FCP, the fracture characteristics of the forged and T5 samples were similar, with many deep dimples on the fracture surfaces, whereas the fracture surfaces of the T4 and T6 samples were covered with lots of lamellar cleavage planes. SEM observations also indicated that the microstructures were distinguished from each other. For the forged and T5 samples, many big bulk w-Mg3Y2Zn3 phases distributed in the Mg matrix. However, for the T4 and T6 samples, due to the solid solution treatment, w-Mg3Y2Zn3 phases were almost completely decomposed and many coarse rod-like  1 precipitates appeared in the interior of the grains. These firmly confirmed that the variation of the microstructures had great influence on the fatigue crack propagation (FCP) characteristics of the Mg-Zn-Y-Zr alloy.
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