DEVELOPMENT OF IN-SITU Al-5%Mg / A1203 COMPOSITE OF HIGH WEAR RESISTANCE FOR APPLICATION IN BEARINGS OF MEDIUM SIZE TRUCKS

Abstract

Aluminum alloy metal matrix composites reinforced with alumina particles are considered as a group of advanced materials for their light weight and good wear resistance properties. Normally, in Al-alloy/ A1203 in-situ composite alumina particles are dispersed in aluminum alloy either through powder metallurgy process or by solidification processing of melt particle slurry. In this study, the in-situ generation of alumina particles has been done via addition of 5% red lead oxide (Pb304) powder in the melt of Al-5 wt.% Mg alloy by stir casting method. The advantages are considered to include better compatibility, improved particle matrix interface and self lubrication due to lead formed by reaction of lead oxide by aluminum. In-situ A1203 particles, so produced, have been mixed well with a stirrer to result in a uniform slurry which has been cast in a vertical rectangular mould. Cast Al-5 wt.% Mg alloy has also been prepared by the same processing route as that of composite. After casting, the samples of as cast in-situ composite has been prepared for metallographic examination and observed under scanning electron microscope (SEM). Microstructures of unetched cast in-situ composite also dark phases which could be lead coated oxide, present in the bright (matrix) phase. Tensile and hardness properties of both in-situ composite and aluminum alloy have been tested. Hardness of Al-5wt.% Mg alloy and Al-5%Mg/A1203 in-situ composite are 56.3±2.0 and 69.8±2.5 VPN respectively. Hardness of in-situ composite is'higher due to the presence of in-situ alumina particles in the matrix as well as unreacted oxide. Alumina particles are hard and brittle by nature. Tensile strength of Al-Mg alloy and in-situ composite are 161.6±3.4 and 58.5±" 2.2 MPa respectively and the corresponding percentage elongations are 7.5±0.8 and 2.4±0.8 % respectively. This shows that the in-situ composite has relatively lower strength and ductility. This is due to the presence of lead and brittle nature of oxides including in-situ alumina particles. EPMA shows, that the lead produced has coated some hard particles. The wear behavior of the both the composite and the alloy follows Archard's law. Wear rates of in-situ composite observed at different loads of 0.5, 1.5, 2.0, and 3.0 kg are quite low compared to those of Al-Mg alloy.