Microstructure, a Limiting Parameter for Determining the Engineering Range of Compositions for Light Alloys: The Al-Cu-Si System

Twelve as-cast alloys of the Al-Cu-Si ternary system were investigated. In all the cases, the microstructural phases observed were: α solid solution of Cu and Si in Al, CuAl2 (θ phase), and silicon crystals. The morphology and distribution of the θ and Si brittle constituents limit the percentages of Cu and Si added in the composition ranges of these commercial alloys.