Microstructure design and heat treatment selection for casting alloys using the quality index

The ductility of casting alloys is usually low and it is thus important to simultaneously assess the effect of changes to the microstructure and heat treatment on both ductility and strength of the material. The use for this purpose of the quality index charts* is common in the casting industry with regard to the Al-Si-Mg casting alloys A356 and A357. An analytical method of generating quality index charts for any alloy system is presented. Applications of the method are illustrated with case studies involving Al-Si-Mg, Mg-Al-Zn, and Al-Si-Cu-Mg casting alloys. The analytically determined charts indicate the limits to microstructural improvement available for each material. The possibility of using the charts to optimize the relation between mechanical performance, chemical composition, solidification conditions, and temper is discussed.