Tri-Route Orchestration of Sr-Modification,Mould Vibration, and T6 Treatment on theMicrostructure and Performance of A356 Alloy

This study examines the cascade effects of chemical modification, mechanical
mould vibration during solidification, and subsequent T6 heat treatment on the microstructural
evolution and multi-property enhancement of A356 Alloy cast via permanent mould casting.
Initially Sodium (Na) modifying flux (2-4 wt %) and Strontium (Sr) elemental modifier (0.01-
0.05 wt %) were implemented to refine the morphology of eutectic silicon; Sr addition at an
optimal concentration of 0.04 wt. % yielded superior eutectic silicon refinement compared to
Na. To further refine the microstructure the optimal Sr-modified melt was subjected to
mechanical mould vibration at frequencies ranging from 40-60 Hz. (0.5 mm amplitude), with
55 Hz identified as peak frequency for mitigating porosity and grain refinement. Finally a T6
thermal profile (Solutionizing at 535°C for 1 h, Quenching in water at room temperature, age
hardening at 154°C for 5 h and allowing it to cool in normal air) was super imposed onto the
optimized Sr + 55 Hz vibration condition. Microstructural characterization via optical and
scanning electron microscopy revealed a distinct transition of eutectic silicon from coarse
acicular needles to a highly refined, globular morphology, alongside enhanced fragmentation of
a α-Al dendrites. This sequential processing approach led to an outstanding concurrent increase
in ultimate tensile strength (UTS), yield strength (YS), ductility, micro-Vicker’s hardness, and
Izod impact energy. While simultaneously decreasing porosity and optimizing electrical
resistivity. The results demonstrate that combining physical and chemical melt treatments with
tailored aging treatments offers a highly effective pathway for manufacturing high-performance
aluminium castings.