STRESSES IN THE EUTECTIC SILICON PARTICLES OF STRONTIUM-MODIFIED A356 CASTINGS LOADED IN TENSION

摘要

Neutron diffraction methods have been successfully used to measure the stress in the eutectic silicon particles in a casting as a function of the applied tensile strain at all strains up to fracture. These measurements have been made for four microstructural conditions - fine and coarse secondary dendrite arm spacings and low and high yield stresses. We have identified and characterized the three classic components of particle stress (ⅰ) the thermal misfit stress, resulting from mismatch in the coefficients of thermal expansion, (ⅱ) the elastic misfit stress, resulting from differences in the elastic constants, and (ⅲ) the plasticity misfit stress, resulting from the plastically inhomogeneous nature of the silicon and aluminum constituents of the casting. We have estimated a lower limit to the fracture strength of the silicon particles and suggest possible explanations for its value.