Effect of yttrium on structure and mechanical properties of Mg alloys

The influence of 2, 4 and 6 wt.% yttrium additions on the mechanical properties and structure of magnesium-based alloys was investigated. The precipitation sequence was studied at 150, 200 and 225 °C by hardness measurements, microstructure investigations and X-ray phase analysis. The hardening of the alloys resulted from the appearance of orthorhombic β′′ transition phase precipitating homogeneously throughout the alloy at 150 °C. The precipitation of the β′ and β (Mg24Y5) phases was observed at dislocations and grain boundaries after prolonged ageing, which both do not contribute to the strengthening effect. At 225 °C, there is only a little increase in hardness.