Effect of yttrium addition on microstructures, damping properties and mechanical properties of as-cast Mg−based ternary alloys

Abstract

In order to reveal the functions of yttrium addition on damping and mechanical properties for Mg−based alloys, the damping and mechanical properties of prepared as-cast Mg−0.6Zr−xY ternary alloys with [Y] = 1.0, 2.0, 3.0, 4.0 and 5.0 mass % have been experimentally measured and theoretically explained through combining the observed microstructures with related theoretical models or mechanisms. The experimental results indicate that added [Y] in the ternary alloys has clear effect on grain refinement. Changing [Y] from 1.0 to 5.0 mass % can effectively decrease the average size of formed equiaxed α−Mg grains from 70.15 to 33.62 μm. The bulk-shaped yttrium-rich phase in α−Mg matrix is mainly composed of Mg24Y5 phase. Increasing [Y] from 1.0 to 5.0 mass % can significantly affect damping properties described by tanφ under the condition of ε > εcr = 2.0 × 10−2, while no visible effect of increasing [Y] on tanφ at ε < εcr = 2.0 × 10−2 can be obtained. Furthermore, the influence of changing strain ε from 1.0 × 10−4 to 1.0 × 10−1 on tanφ complies with dislocation pinning theory or the G−L model. Meanwhile, increasing [Y] in the ternary alloys shows the similar variation tendency for relationship between tanφ and temperature T from ambient temperature Tam to 673 K (400 °C). The effect of varying temperature T from Tam to 673 K (400 °C) on tanφ for the ternary alloys can be well explained by the grain boundary damping mechanism. In addition, increasing [Y] from 1.0 to 4.0 mass % can effectively promote both yield strength Rp0.2 and ultimate tensile strength Rm, however further increasing [Y] from 4.0 to 5.0 mass % cannot result in an obviously increasing tendency for Rp0.2 and Rm. The similar results of adding [Y] on elongation A can also be obtained with [Y] = 3.0% as a criterion. Meanwhile, the measured results of adding [Y] on Rp0.2 and Rm for the ternary alloys can be well explained by the grain boundary strengthening and solid solution strengthening mechanisms. Therefore, the optimal chemical composition for as-cast Mg−Zr−Y ternary alloys with higher damping properties and greater tensile properties is recommended to be Mg−0.6Zr−4.0Y.