Investigations were carried out to ensure the granulated blast furnace (GBF) slag as an alternative mould material in foundry industry by

assessing the cast products structure property correlations. Sodium silicate-CO2 process was adopted for preparing the moulds. Three

types of moulds were made with slag, silica sand individually and combination of these two with 10% sodium silicate and 20 seconds CO2

gassing time. A356 alloy castings were performed on these newly developed slag moulds. The cast products were investigated for its

metallography and mechanical properties. Results reveal that cast products with good surface finish and without any defects were

produced. Faster heat transfers in slag moulds enabled the cast products with fine and refined grain structured; and also, lower Secondary

Dendrite Arm Spacing (SDAS) values were observed than sand mould. Slag mould casting shows improved mechanical properties like

hardness, compression, tensile and impact strength compared to sand mould castings. Two types of tensile fracture modes, namely

cleavage pattern with flat surfaces representing Al−Si eutectic zone and the areas of broken Fe-rich intermetallic compounds which appear

as flower-like morphology was observed in sand mould castings. In contrast, GBF slag mould castings exhibit majority in dimple fracture

morphology with traces of cleavage fracture. Charpy impact fractured surfaces of sand mould castings shows both transgranular and

intergranular fracture modes. Only intergranular fracture mode was noticed in both GBF slag and mixed mould castings.