Effect of combined addition of Si and Sb on the microstructure and creep properties of AZ91 magnesium alloy

Addition of silicon (0.5 wt.%) together with small amount of antimony (0.2 wt.%) to AZ91 alloy has been carried out to study its effect on the microstructure and creep properties at 150 and 200 °C. The results show that the combined addition (Si and Sb) introduces fine polygonal shaped Mg2Si precipitates at the grain boundaries and in the grains. Besides, the addition suppresses the precipitation of discontinuous Mg17Al12 phase during ageing treatment. These lead to an improvement in creep behavior of AZ91 at 150 and 200 °C temperatures. Moreover, extended steady state creep, reduced minimum creep rate and total creep strain are also observed with the combined addition. Presence of fine and stable Mg2Si precipitates and suppression of discontinuous precipitation are the possible reasons for the improvement in creep properties.