Influence of Chill Materials on Microstructure and Mechanical Properties of Aluminium-Silicon Alloy Casting

Abstract

Microstructure and mechanical properties of aluminium alloy casting is influenced by the rates of solidification and cooling. Solidification of molten metal in casting is improved by the use of chill materials. Therefore, this study investigates the influence of chill materials on microstructure and mechanical properties of aluminium-silicon alloy using green sand casting technique. Green sand moulds were designed with incorporation of external chills. Brass, Mild Steel and Cast Iron were selected as chill materials for investigation. Plate of aluminium-silicon alloy castings were produced and cooled using chills, each of which were made into nine (9) blocks of same shapes but varying thicknesses of 10 mm, 15 mm and 20 mm. For every chilled casting, test samples were taken at three distances from the point of contact between castings and chills to the free ends. Evaluation of the microstructure and mechanical properties of the samples were carried out. The results revealed that Ultimate Tensile Strength (UTS) and Brinell Hardness Number (BHN) decreased with increase in distances from the edges of contact between the chills and castings as well as increased with increase in chills thicknesses. The results show that Brass chill was the most effective, having increased the UTS (18%) and BHN (53%). Second to Brass was Cast Iron chills with an improved UTS (11%) and BHN (40%). Mild Steel chill was the least effective, having raised the UTS (8%) and BHN (16%). Therefore, the use of Brass chill material is most suitable for green sand casting of Aluminium-silicon alloy; in contrast to other chill materials investigated.