| With the rapid development of modern industry and transportation, vibration and noise pollution has become one of the serious environmental problems. In order to reduce vibration and noise, controlling the vibration source is the most important. The high damping and high strength magnesium alloy is the goal of this thesis. Pure magnesium and Mg-Al-Zn alloys were chosen to be the research object. Optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) were applied to observe the microstructures. The mechanical properties were tested on versatile testing machine. Temperature and strain amplitude dependence of damping capacities were investigated by a dynamic mechanical analyzer (DMA). To provide the beneficial reference for developing high damping and high strength magnesium alloy, the influence of deformation processes, heat-treatments and Yttrium addition on microstructures and properties of magnesium alloy was revealed.Firstly, the effects of bending deformation on damping capacity of pure magnesium were studied. During bending, a lot of tangles of dislocations and twins which had bad effect on the damping capacity were found in the matrix of pure magnesium. After annealing, tangles of dislocation is released and significant effects of recrystallization is obtained, so damping properties are greatly enhanced and the damping capacity of some sample even exceeds pure magnesium without deformation process.Based on this, the microstructure, mechanical properties and damping capacity of Mg-Al-Zn magnesium alloy with and without homogenization annealing under the first extrusion, second extrusion and forging states were researched respectively. The results show that there are nearly no differences in the mechanical property of magnesium alloys which undergo above three different processes, however, the obvious change of damping capacities is observed. When the strain amplitude is 5×10-3, the damping capacities of the forging state are five times more than the second extrusion state, which is caused by increase of grain size and elimination of tangles of dislocations.Next, after heat treatment, the mechanical properties and damping capacity of above deformed alloy was investigated. The strength of deformed Mg-Al-Zn alloy with T5 and T6 heat treatment is markedly improved,and deformed Mg-Al-Zn alloy with T6 heat treatment still maintains a certain plasticity. The strain-amplitude dependent damping of T4 and T6 treated alloy also greatly improves. The influence of heat treatment on damping capacity of Mg-Al-Zn alloy can be well explained by G-L theory.Lastly, the effects of rare earth element Y on microstructure, mechanical properties and damping capacity of the extruded Mg-Al-Zn alloys were researched. The results show that with the addition of Y, the grain size is obviously increased and new phase of Al2Y precipitate. The yield strength of alloys does not decrease but improve in spite of the increase of grain size, the reason is the precipitation of new phase of Al2Y. The damping capacities of Mg-Al-Zn-xY alloys at room temperature are significantly improved with the addition of Y. When the strain amplitude is 5×10-3, the damping capacity of Mg-Al-Zn-0.5Y alloy increases 69% than that of Mg-Al-Zn alloy. In the high temperature damping tests, the new phase of Al2Y enhances the anti-softening properties, the Al2Y particles make Mg-Al-Zn-0.5Y alloy begin softening until the temperature over 300℃.
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