Effect of yttrium on microstructures and properties at elevated temperature of Mg-0.8Zr-0.35Zn alloys

The effects of Y addition on microstructures and properties of as-cast and solid solution and aging treated Mg-0.8Zr-0.35Zn alloys at elevated temperature (250°C) were investigated by the use of XJG-04 optical microscopy, JCXA-733 electron probe, D/max-rB X-ray diffractometer (XRD) and WDW-200 electronic universal material testing machine. The results show that the microstructures of as-cast and heat treated Mg-0.8Zr-0.35Zn alloys with Y addition are refined and a new phase, Mg₂₄Y₅, is formed. At 250°C, the strength at elevated temperature of the alloys increases with increasing amount of Y addition, but relative elongation and area reduction decreases. The tendency of brittle fracture of fractured surface at elevated temperature is enlarged and fracture is changed from ductile into cleavage.