This article begins with a schematic illustration of a eutectic system in which the two components of the system have the same crystal structure. Eutectic systems form when alloying additions cause a lowering of the liquidus lines from both melting points of the pure elements. The article describes the aluminum-silicon eutectic system and the lead-tin eutectic system. It discusses eutectic morphologies in terms of lamellar and fibrous eutectics, regular and irregular eutectics, and the interpretation of eutectic microstructures. The article examines the solidification of a binary alloy of exactly eutectic composition. It concludes with a discussion on terminal solid solutions.

This article presents the binary eutectic phase diagram to understand the various structures that evolve in a binary eutectic system during solidification. It describes the various classifications and solidification principles of the eutectic structures. The formation of halos in eutectic microstructures of most alloy systems is also discussed.

This article focuses on aspects that are important for the commercial production of castings. It discusses the modification process in hypoeutectic and eutectic alloys that differ only in the relative volume fraction of primary aluminum and aluminum-silicon eutectic. The article explains how modification changes porosity formation in a casting. It describes the mechanisms responsible for silicon modification, as well as the modifications and changes in eutectic nucleation and the eutectic grain structure. The article reviews the usage of strontium in foundry practices. The growth of silicon eutectic is described to explain effects ancillary to silicon modification. The article also examines the effects of elements, such as phosphorus, antimony, bismuth, magnesium, boron, and calcium, on the silicon structure.

The most common aluminum alloy systems are aluminum-silicon, aluminum-copper, and aluminum-magnesium. This article focuses on the grain structure, eutectic microstructure, and dendritic microstructure of these systems. It provides information on microsegregation and its problems in casting of alloys. The article also illustrates the casting defects such as macroporosity, microshrinkage, and surface defects, associated with the alloys.