Creep Behavior of Mg–10Gd–xZn (x=2 and 6 wt%) Alloys

Abstract

Creep behavior of Mg–10Gd–xZn alloys was investigated with two Zn contents, 2 and 6wt%. The as cast microstructure of alloys contained (Mg, Zn)3Gd phase at the interdendritic regions and long period stacking ordered (LPSO) phase in the matrix. Increase in the Zn content from 2% to 6%, increased the volume fraction and morphology of second phase [(Mg,Zn)3Gd]. Creep testing at 250 and 300°C with stress levels between 50 and 120MPa indicated that increase in Zn content or temperature reduced the creep performance of the Mg–10Gd–xZn alloys. The minimum creep rate of Mg–10Gd–2Zn was one order less that of Mg–10Gd–6Zn. Dynamic precipitation was found in both the alloys during creep deformation at 250°C and strengthened the alloys: prismatic platelets (Mg5Gd) were observed perpendicular to the LPSO phase in Mg–10Gd–2Zn alloy whereas basal oval precipitates (ternary composition) parallel to the LPSO occurred in Mg–10Gd–6Zn alloy. The dynamic precipitates were not observed in alloys during creep at 300°C. Ternary bulk precipitates at the LPSO phase was observed in both alloys and at all testing conditions which facilitated the cracking during deformation. More continuous second phase at the interdendritic boundaries facilitated easy cracking in Mg–10Gd–6Zn alloy and hence reduced the creep performance.