The Reason of Formation of Gas Porosity in Composite Castings with an Aluminum Alloy Matrix

The paper presents the types of gaseous porosity occurring in composite castings in result of occlusion of atmospheric air during saturating of the composite reinforcement and liberation of gases while cooling and solidifying of matrix metal of the composite. A mechanism of gas occlusions formation is presented, as well as the factors causing the changes in their volume under the conditions of varying pressure in characteristic locations of the composite casting in the course of its production are discussed. The results of the analysis of gas liberation from the composite matrix, nucleation, and growth of the blowholes are provided. Conclusions resulting from the theoretical consideration are illustrated by the examples of porosity forms found by the authors in experimental composite castings.