Modeling of diffusion and intermetallic phase formation in bimetallic applications

Lightweight product design and manufacturing will increasingly use bimetallic structures which can meet more complex performance requirements. Overcasting is a key technology to integrate bimetallic applications in Mg-Al and Al-Fe systems. However, it is not well understood for the thermodynamic and diffusional behaviors and intermetallic compound (IMC) formation in these systems. In this presentation, complete and self-consistent thermodynamic and atomic-diffusional databases have been constructed using CALculation of PHAse Diagram (CALPHAD) modeling and experimental data in literature. Based on the above assessment of the Al-Mg and Al-Fe systems, overcasting process and subsequent heat treatment parameters are optimized for these bimetallic systems to provide metallurgical bonding. The detailed microstructure evolution during casting and annealing, including the formation and growth of various intermetallic phases, was experimentally observed and predicted using CALPHAD and diffusion modeling. The modeling work using DICTRA and pydiffusion codes proved efficient in predicting the diffusion profiles and lengths and intermetallic phase formation in bimetallic samples during casting and annealing. The precise diffusion modeling in Mg/Al and Al/Fe interfaces provides an efficient way to optimize/control the interfacial microstructure of the bimetallic applications for improved interfacial bonding.