Effect of Sn on the microstructure and compressive deformation behavior of the AZ91D aging alloy

The effect of Sn on the microstructure and compressive deformation behavior of aging AZ91D magnesium alloy was investigated. The results show that the discontinuous precipitation occurs near the grain boundary in the form of lamellar precipitates of the Mg17Al12 phase. These precipitates alternatively lie in the α-Mg matrix perpendicular to the grain boundaries. With an increase in the Sn content, the cellular discontinuous precipitation can be efficiently suppressed, such that no discontinuous precipitation is observed when the Sn content is increased to 2 wt.%. The AZ91D aging alloy has a higher ultimate fracture strength than the base 2%Sn alloy due to the large numbers of grains containing the cellular discontinuous precipitation forming nearby the grain boundaries. In these regions the β phase can effectively hinder the dislocation movement. Conversely, the soft behavior induced by a high fraction of twins is the main reason that the strength of 2%Sn alloy is lower than that of the AZ91D alloy.