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.