Creep of Mg-Zn-Al-Alloys

Summary

Due to their low melting point, the application of most commercially available magnesium alloys is limited to temperatures below 120 °C. Much progress in developing new creep resistant die casting alloys has been made in the last few years. However, the basic mechanisms of creep in these alloys are still not well understood. In an attempt to elucidate these basic mechanisms, we have investigated the creep behavior of a Mg alloy ZA85 with 8 wt.% zinc and 5 wt.% aluminum as a model system. ZA85 has been shown to be comparable to common aluminum rich AZ alloys concerning die castability and mechanical properties at room temperature and, in addition, to offer a better creep resistance. Recent investigations have shown that the creep strength of this alloy system can be strongly improved by the addition of further alloying elements. From AZ91 it is well known that the casting process has a strong influence on the creep behavior. Therefore, a fine and a coarse grained ZA microstructure was processed and investigated. Creep testing was performed under compressive load at stresses ranging from 50 to 100 MPa and temperatures between 130 and 190 °C.