As-cast structures and mechanical properties of impeller-mixed, chill-cast, leaded aluminium—silicon alloys

Abstract

Aluminium—silicon—lead alloys with silicon content from 2 to 20 wt% and lead from 2 to 10 wt% were prepared by an impeller-mixing, bottom-discharge, chill-casting technique. Casting parameters such as mixing speed, temperature, and time were optimised. A mixing speed of 16.67 Hz (1000 r.p.m.) and a superheat temperature of 100 °C above the liquidus, for a period of 5 min, was found to be suitable for the preparation of the alloys. As-cast microstructures revealed equiaxed morphology of aluminium-rich dendrites embedded in the matrix of eutectic aluminium—silicon. Lead was found to be uniformly distributed in interdendritic regions as fine globules or patches associated with silicon particles. The room-temperature tensile and compressive strengths and hardness of the leaded aluminium—silicon alloy decreased and elongation increased with increasing lead content of the alloy. The scanning electron microfractographs of tensile specimens revealed the increasing ductile nature of fracture as lead content increased.