Analysis of the effect of Si content on the creep response of an Mg-5Al-Mn alloy

The present study aims at investigating the effect of small additions (0.3, 0.5, 0.8 and 1.5%) of Si on the creep response of an AM50 alloy. Die-cast samples not previously heat-treated were subjected to tensile tests at room temperature and to constant load creep tests at 423 and 398 K. The effect of chemical composition was investigated by testing five alloys with rising Mg content, from 0 (basic AM50 alloy) to 1.5%. Irrespective of Mg content, the creep curves exhibited a well-defined primary stage followed by a short secondary region and by a short tertiary stage that led to fracture without extensive necking. Addition of 0.3% Si hardly affected creep strain rate, while greater additions induced a substantial increase in creep strength, an effect that was partially offset by a decrease in strain to fracture.