Interfacial phenomena and microstructure evolution during solidification of binary and ternary Al–Mg–Si alloys cast with titanium carbonitride

Abstract

In this work the microstructural evolution of Al–Mg 2Si alloys cast with titanium carbonitride (TiCN) nano-powder was studied, based on Al(Mg)–TiCN and Mg(Si)–TiCN model systems. From the investigation of the model systems, it is concluded that the presence of TiCN leads to the formation of a Mg-rich (or pure Mg) bulk liquid layer in the alloy at the melt–TiCN interface, before solidification begins. The driving force for the formation of the interfacial Mg-rich layer is the reduction of the total interface energy. It is postulated that this layer forms due to the interaction between Mg segregated at the alloy–TiCN interface with Mg-rich Al–Mg-clusters and Si-rich Mg–Si-clusters from the molten alloys. It is concluded that a Mg-rich bulk layer also forms at the Al(Mg,Si)–TiCN interface in cast Al–Mg 2Si alloys, which prevents nucleation of Mg 2Si on the TiCN particles.