The majority of the work on the effect of modification on microporosity deals with two extremes, either unmodified alloys or fully modified allosy. In the present work the effect of several different levels of strontium on the amount of microporosity in A356 aluminum-silicon foundry alloy is studied. The objective is to determine whether changes in pore properties are due to (a) chemical effect (i.e. the amount of strontium in the casting), or (b)microstructural effect (i.e. the modification of the eutectic structure). In addition, nearest neighbor cluster analysis was used to distinguish between the effect on gas and shrinkage porosity. It was shown that the percentage porosity increases with strontium concentration. This is due to an increase in gas porosity. The pore density (pores/cm~20 decreases as a function of the microstructural effect of strontium. This is due to a decrease in the number of shrinkage pores. The number of gas pores remains constant with modification. The average and maximum pore sizes increase with the strontium concentration, and this increase is greater than the decrease in pore density. Finally, small amounts of strontium alter the pore shape, making the pores much more equiaxed.
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