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 castabi lity to the alloy, and increases the tensile strength of the alloy, much ne eds to be done to improve the understanding of the structure-property relat ionships in castings. This paper deals with the application of a microstruc tural 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 an d the aluminum matrix. The highest stress in the matrix increases with incr easing particle size for a given volume fraction of silicon particles. Ther efore, the yield strength of a microstructure containing coarse particles w ould be lower than one containing fine particles. Once the silicon particle s with large aspect ratios crack or the microstructure containing large sil icon particles yield. the effective stiffness of the aluminum matrix decrea ses which significantly increases the average stress in the silicon particl es and the highest stresses in both the silicon particles and the aluminum matrix. This indicates that once the matrix yields, the potential for parti cle cracking increases dramatically. (C) 2001 Elsevier Science B.V. All rig hts reserved.