The structure and mechanical behavior of the Mg-Mg₂Ni eutectic composite

Abstract

The structure and mechanical behavior of the unidirectionally-solidified Mg-Mg₂Ni eutectic have been studied over a range of solidification rates frorm 3 to 250 cm per hr. The yield and ultimate strengths of the composite tend to increase with increasing solidification rate and microstructural fineness. The mechanical behavior, however, is also strongly influenced by changes in eutectic crystallography and matrix deformation mode which occur with increasing solidification rate. When yielding of the matrix is controlled by slip, the effect of solidifica tion rate on composite yield strength can be quantitatively accounted for by an analysis based on a simple dislocation model. Under some conditions, however, yielding of the ma trix occurs by$\left\{ {11\bar 24} \right\}$ twinning, resulting in markedly different mechanical properties. When solidified at 250 cm per hr the Mg-Mg₂Ni eutectic has higher yield and ultimate strengths than the strongest commercial magnesium alloys, but its poor ductility and corrosion resistance will severely limit its use as a high performance engineering material.