Analysis of stresses in aluminum–silicon alloys

Two-phase aluminum–silicon-based alloys are widely used for premium quality castings for aerospace and automotive applications. While it is clear that silicon improves fluidity in the molten state, providing excellent castability to the alloy, and increases the tensile strength of the alloy, much needs to be done to improve the understanding of the structure–property relationships in castings. This paper deals with the application of a microstructural finite element method and the OOF program to study the effect of size and shape of silicon particles on the stresses in the silicon particles and the aluminum matrix. The highest stress in the matrix increases with increasing particle size for a given volume fraction of silicon particles. Therefore, the yield strength of a microstructure containing coarse particles would be lower than one containing fine particles. Once the silicon particles with large aspect ratios crack or the microstructure containing large silicon particles yield, the effective stiffness of the aluminum matrix decreases which significantly increases the average stress in the silicon particles and the highest stresses in both the silicon particles and the aluminum matrix. This indicates that once the matrix yields, the potential for particle cracking increases dramatically.