Microporosity, a serious defect in Al-Si based castings, severely prevents their widespread applications in many critical conditions. The use of criteria functions to predict quantitatively microporosity level holds promise. To date, an ideal criteria function has yet to be obtained. In the present work, microporosity distribution in three prominently used hypoeutectic Al-Si alloys (319, 356 and 332) was investigated. The prediction effectiveness of single solidification parameter and existing criteria functions was evaluated by correlating thermal data of simulation studies to experimentally obtained microporosity values. Two new criteria functions are proposed based on experimental observation and multivariable regression analysis. The results indicate that thermal parameter-based criteria functions may be used to predict the microporosity in Al-Si castings but have their limitations. A general criteria function tf1.18 Vs1.13 (tf, local solidification time; Vs, solidification velocity) can be applied to predict microporosity for the family of hypoeutectic Al-Si casting alloys within a certain error.
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