Damping behaviors of as-cast and solution-treated AZ91-Ca magnesium alloys

The effects of solution treatment on the microstructure and damping capacity of AZ91 and AZ91-0.4%Ca alloys were investigated. In the as-cast state, the Ca addition contributed to the suppression of discontinuous β precipitation and to the formation of an Al2Ca phase; however, it reduced the amount of compound particles by decreasing the β phase content. After the solution treatment, the AZ91 alloy had only a trace amount of Al8Mn5 particles, whereas β and Al2Ca phases are still observed in the AZ91-0.4%Ca alloy. In strain-amplitude independent region, the solution-treated alloys showed slightly higher damping levels than the as-cast alloys, regardless of Ca addition. In the strain-amplitude dependent region, the Ca-added alloy exhibited a better damping capacity than the Ca-free alloy in as-cast state; however, after solution treatment, the respective damping behaviors were reversed. From the microstructural evolution before and after the solution treatment, the solute concentration in the α-Mg matrix and the number density of compound particles are thought to be the principal factors influencing damping behaviors of the strain-amplitude independent and dependent regions, respectively.