The microstructure-strength relationship in a deformation processed Al-Ca composite

An Al-9 vol% Ca composite was produced by powder metallurgy and deformation processing. The Al-Ca composite was extruded, swaged and wire drawn to a deformation true strain of 13.8. Both Al and Ca are face-centered cubic, so the Ca second phase deformed into continuous, nearly cylindrical filaments in the Al matrix. The formation of intermetallic compounds, filament coarsening, and spheriodization at elevated temperature was observed by scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. Both the thickness and spacing of the Ca filaments decreased exponentially with increasing deformation. The ultimate tensile strength of the composite increased rapidly with increased deformation, especially at high deformation processing strains. The relation between deformation true strain and ultimate tensile strength is underestimated by the rule of mixtures; a modified Hall-Petch barrier strengthening model was found to fit the data better.