Evaluation of the microstructure, secondary dendrite arm spacing, and mechanical properties of Al–Si alloy castings made in sand and Fe–Cr slag molds

Abstract

The microstructure and mechanical properties of as-cast A356 (Al–Si) alloy castings were investigated. A356 alloy was cast into three different molds composed of sand, ferrochrome (Fe–Cr) slag, and a mixture of sand and Fe–Cr. A sodium silicate–CO2 process was used to make the necessary molds. Cylindrical-shaped castings were prepared. Cast products with no porosity and a good surface finish were achieved in all of the molds. These castings were evaluated for their metallography, secondary dendrite arm spacing (SDAS), and mechanical properties, including hardness, compression, tensile, and impact properties. Furthermore, the tensile and impact samples were analyzed by fractography. The results show that faster heat transfer in the Fe–Cr slag molds than in either the silica sand or mixed molds led to lower SDAS values with a refined microstructure in the products cast in Fe–Cr slag molds. Consistent and enhanced mechanical properties were observed in the slag mold products than in the castings obtained from either sand or mixed molds. The fracture surface of the slag mold castings shows a dimple fracture morphology with a transgranular fracture nature. However, the fracture surfaces of the sand mold castings display brittle fracture. In conclusion, products cast in Fe–Cr slag molds exhibit an improved surface finish and enhanced mechanical properties compared to those of products cast in sand and mixed molds.