On tailored microstructure in AA 2024 alloy during in-situ microwave casting

In the present study, application of microwave energy was explored for tailoring the microstructure in AA 2024 alloy through directional solidification route. Microwave transparent (alumina) and absorbing (graphite) mould materials were utilized to investigate the effect of microwave interaction (electric and magnetic field components) with AA 2024 alloy on microstructure evolution in terms of dendrite size distribution and formation of eutectic phase. Results showed more pronounced eutectic phase gradient was developed using alumina mould. On the other hand, a more uniform distribution of eutectic phase and grain size was observed with graphite mould. The development of the eutectic phase gradient is attributed to the effective microwave interaction with the AA 2024 alloy melt during solidification. This is primarily associated with the formation of an additional flux at the solid-liquid (S/L) interface of the alloy under the effect of magnetic field and an enhancement in diffusion flux due to mass transport caused by electric field component of microwave. Formation of AlCu, Al₂Cu, and Al₂CuMg intermetallic phases in both alumina and graphite mould casts was confirmed. Significantly higher hardness was observed at the higher eutectic phase sites within the alumina mould cast, whereas graphite mould casts exhibited better tensile properties.