Investigations on the use of salt as a sustainable moulding material for AlSi12 gravity casting

This study investigates additive-free table salt as a sustainable and cost-efficient mould material for gravity casting of AlSi12 alloy, targeting mould volumes and component sizes significantly larger than those reported in previous studies. Salt moulds were fabricated by embedding a 3D-printed expendable wax model in fine-grained NaCl combined with a saturated salt solution, followed by a multi-stage drying and burnout procedure. The salt mould material reached a maximum compressive strength of 3.3 MPa, comparable to the green strength of conventional ceramic moulds. A comparative gravity casting study using AlSi12 at 750 revealed that salt and sand moulds yield similar ultimate tensile strengths (135 MPa vs. 140 MPa), elongation at fracture, and hardness. The higher thermal conductivity of the salt mould resulted in an approximately doubled cooling rate (12.7 K s −1 vs. 6.2 K s −1 ), producing a finer microstructure with a reduced Secondary Dendrite Arm Spacing (36.7 µm vs. 44 µm). Additionally, a surface smoothing effect was observed in salt castings, reducing average roughness from in the wax model to in the casting. These results demonstrate the feasibility of additive-free table salt for larger-scale aluminium gravity casting with mechanical and microstructural properties comparable to conventional sand casting.