Mechanical and Thermal Behavior of Chilled Aluminum Alloy (Lm-25) Reinforced With Borosilicate Glass Particulate Metal Matrix Composites (MMCs)

Hemanth J

Published on: 2019-12-31

Abstract

Present investigation aims at developing chilled aluminum alloy (LM-25) reinforced with borosilicate glass using stir casting method. Matrix alloy was melted in a composite making furnace to a temperature of about 700oC to which preheated reinforcement particles was added (3 wt.% to 15 wt.% in steps of 3 wt.%), stirred well and finally poured in to a AFS standard mold containing different metallic and nonmetallic end chills placed judiciously for directional solidification. The resulting chilled composites were subjected to microstructural, EDAX, mechanical (strength and hardness) and thermal (carburization, coefficient of thermal expansion and thermal conductivity) tests. Results of the microstructural and EDAX analysis indicate that the chilled castings were sound with good distribution of particles and bonding between ceramic particulate (reinforcement) material and Al alloy matrix (LM-25) possessing excellent isotropic properties without any shrinkage or micro porosity. Mechanical characterization indicate that both strength (170 Mpa) and hardness (159 HV) was maximum in the case of copper chilled MMC containing 9 wt. % reinforcement. It is observed that because of the ceramic reinforcement in aluminum alloy, the coefficient of thermal expansion (CTE) decreased linearly with reinforcement addition whereas the thermal conductivity was decreased. Carburization tests (which is time dependent) reveal that near the interfacial regions, a flakey type of carbon layer was present that has refined the microstructure and slightly increased the hardness.