This study investigates the effect of scandiumScandium (Sc) additions on the microstructureMicrostructure and tensile propertiesProperties of Al–7Si–0.3Mg (A356) alloy under both as-cast and T6 heat-treated conditions. Sc was introduced at 0.2, 0.4, and 0.6 wt.% to identify the optimal composition and evaluate fadingFading behaviour during extended melt holdingHolding. Microstructural characterisation revealed that Sc additions refined α-Al dendrites, modified eutecticEutectic Si, and suppressed needle-like Fe-rich intermetallicsIntermetallics. The 0.4 wt.% Sc alloy exhibited the most balanced propertiesProperties, achieving yield strengthStrength of ~ 124 MPa, ultimate tensile strengthTensile strength (UTS) of ~ 225 MPa, and elongation of ~ 9% in the as-cast condition. After T6 treatment, the YS and UTS of 0.2 wt.% Sc alloy increased to ~ 261 MPa and ~ 324 MPa, respectively. Alloys with 0.6 wt.% Sc formed coarse AlSi₂Sc₂ intermetallicsIntermetallics, which reduced both strengthStrength and ductility. FadingFading tests confirmed that grain size and strengthStrength remained stable for up to 240 min of melt holdingHolding, with only ductility decreasing after 90 min due to porosity linked with higher density indexDensity index. These results demonstrate that Sc in the 0.2–0.4 wt.% range effectively enhances mechanical propertiesMechanical properties of A356 alloys without fadingFading like conventional grain refiners, offering strong potential for industrial adoption.