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

This paper examines the room-temperature microstructure and mechanical prop erties of dispersion-strengthened-cast magnesium (DSC-Mg) containing 30 vol .% of 0.33 mu m yttria dispersoids. The dispersoids are reasonably well dis tributed 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 pinnin g. The Young's modulus measured ultrasonically agrees well with the predict ion of the Eshelby composite model. Premature failure in tension is observe d in extruded DSC-Mg, due to casting porosities. In compression, strain sof tening after yield is observed in extruded DSC-Mg, which may be explained b y the tension/compression asymmetry in wrought magnesium materials. Both ca st and extruded DSC-Mg are much stronger in compression than most existing magnesium alloys and composites. The strengthening contributions from the d ispersoids, grain boundaries and thermal mismatch dislocations are discusse d. (C) 2000 Published by Elsevier Science S.A. All rights reserved.