Papers by Author: Gui Ying Sha

Abstract: Through stress-controlled fatigue testing under different stress amplitudes, effects of stress amplitude on the fatigue life and crack propagation mechanism of the extruded Mg-3Al-2Sc alloy were investigated. The results show that, within the stress range of 13.5~82.5 MPa and stress ratio of 0.2, the fatigue life of the alloy decreases and growth rate of fatigue crack increases with increasing stress amplitude. Cleavage fracture mode dominates the crack initiation area and stable crack propagation area. For the final rapid fracture area, the fatigue fracture is combined mode of semi-cleavage and cleavage as well as intercrystalline fracture.

Abstract: In this paper, the effects of rolling and annealing on the high speed impact deformation behavior of the Mg-3%Li-1%Ce alloy were investigated by using the Hopkinson compressive bar. The results showed that the microstructures of the as-rolled alloy consisted mainly of deformed grains, with some secondary Mg₁₂Ce particles in grain interior or on grain boundary. After annealing at 350 °C for one hour, static recrystallization happened and grains were significantly refined. For the annealed alloy, the impact stress-strain behavior is non-sensitive to strain rate in the strain rate range of 1000~1750 s^-1. Under the strain rate of 2250 s^-1, the dynamic behavior demonstrated negative strain rate effect. The occurrence of cracking was supposed to be the main reason for the strain rate softening effect.

Abstract: In this paper, the impact deformation behavior of the as-rolled and annealed Mg-3%Li-1%Nd alloy was investigated by using the Hopkinson compressive bar. The effects of rolling and annealing on the high speed impact deformation behavior were analyzed. The relationship between microstructure evolution and impact fracture mechanism was discussed.

Abstract: Heavy deformation plus micro alloying could be an effective way to obtain ultrafine grain structure of metals. In the present work, an Al-Cu-Mg alloy was microalloyed with Zr to obtain homogeneous precipitates and then heavily deformed by conventional forging at high temperature. The possible refining processing routes were studied and the superplasticity behaviors of the alloy was investigated. Results show that the micro alloyed alloy can be stably refined to 3-5μm under conventional processing routes. The Al-3Zr precipitates act both as additional sites to enhance recrystallization nucleation rate and pins to impede grain growth to increase the thermal stability of the fine grain structure. However, as the Al3Zr precipitates remains along grain boundaries, the superplastic capability of the material is not high. At 430°C with 1×10-4S-1 strain rate, the elongation obtained was 260%.

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.

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.