| Abstract:Mg-Li alloys, which possess high specific strength and rigidity, good damping capacity and so on, have been widely explored in application of aircraft, electronics and communication industries. This thesis aims at investigating the effects of the preparation process and the Y element on the quality of and mechanical stability of boron compound reinforced Mg-Li based composite ingots.The result shows that the quality of Mg-Li composite ingot is influenced by the factors of gas amount, magnesium evaporation volume and stirring time. The quality of ingot can be improved by decreasing reaction time, increasing the height of ingot, and adding Y element.The grain size of alloy matrix can be significantly refined with the addition of0.5%Y, which mainly exists as A12Y. The highest tensile strength (248.7MPa), yield strength (217.5MPa), elasticity modulus (51.7GPa), bending strength (303.4MPa), and superior elongation (21%) can be achieved by adding1%Y in composite.The composite has been aged for a year to investigate the age softening behavior of matrix alloy. When adding0.5%Y in composite, the decrease amplitude of tensile strength decreases by19.4%at room temperature. By tensile experiments at25℃,60℃and100℃, the result shows adding0.5%Y in composite, the decrease amplitude of tensile strength decreases by23.4%and13.3%at60℃and100℃. Therefore, the improvement of Y element to the high temperature mechanical property of the composite is pronounced. The addition of Y could enhance the age softening resistance and the mechanical property of the composite.XRD analysis revealed that the strengthening phases are composed of the LiB, LiBC and Mg2B. The validity of the composing can be further verified, the theoretical density of the composite has been reasonable calculated as well.The second phase strengthening is the leading strengthening factor of the composite by analyzing the characteristic and composition of the composite, and calculating models of strengthen mechanisms. |
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