Microstructure and mechanical properties of magnesium containing high volume fractions of yttria dispersoids

This paper examines the room-temperature microstructure and mechanical properties of dispersion-strengthened-cast magnesium (DSC-Mg) containing 30 vol.% of 0.33 mu m yttria dispersoids. The dispersoids are reasonably well distributed in both cast and extruded materials and the extruded matrix grains size is about 0.88 mu m, in agreement with existing models on Brain pinning. The Young's modulus measured ultrasonically agrees well with the prediction of the Eshelby composite model. Premature failure in tension is observed in extruded DSC-Mg, due to casting porosities. In compression, strain softening after yield is observed in extruded DSC-Mg, which may be explained by the tension/compression asymmetry in wrought magnesium materials. Both cast and extruded DSC-Mg are much stronger in compression than most existing magnesium alloys and composites. The strengthening contributions from the dispersoids, grain boundaries and thermal mismatch dislocations are discussed. (C) 2000 Published by Elsevier Science S.A. All rights reserved.