DEVELOPMENT OF IN-SITU AI-Al2O3 METAL MATRIX. NANOCOMPOSITE

Abstract

Particle reinforced metal matrix composites (MMCs) are an important class of composite materials. During last decades, particulate MMCs have found special industrial applications. It is hypothesized that the properties of metal matrix composites with embedded nano-sized ceramic particles (1.0-100 nm), termed metal matrix nano-composites (MMNCs), would be enhanced considerably even with a very low volume fraction. One of the best ways for producing cast particulate nanocomposites is in-situ methods. The advantage is considered to be of higher compatibility and improved particle matrix interfaces. A commonly adopted in-situ method involves reaction between a metal oxide and aluminium to produce alumina particles. By completing the alumina formation reaction, the reduced metal usually further reacts with Al to form intermetallic phases, which also act as reinforcements in the matrix of the composite. Because of the formation of ultrafine and stable ceramic reinforcements, the in-situ MMNCs are found to exhibit excellent mechanical properties. In this study, in-situ particle reinforced aluminium based cast composites have been synthesized by dispersion of externally added Manganese Dioxide (Mn02) particles into molten aluminium in different weight percent. The Mn02 particles were milled in a planetary ball mil to reduce its size from around 10-15μm to 10-50nm. Then these Mn02 particles were characterized by FE-SEM and EDAX analysis. Four castings each by reinforcing nano and micro size Mn02 particles and one of base metal (A1-5%Mg) were developed. Alumina particles (A1203) form through chemical reaction of Mn02 particles with molten aluminium. Around 5% Mg was also addeu'to the Al matrix to enhance the wettability of alumina particles. Simultaneously, the chemical reaction also releases Mn, which dissolves into molten aluminium during solidification. FE-SEM, EDAX, tensile testing, and machinability using conventional drilling method has been studied to determine the properties of the nanocomposites compared to the conventional microcomposites and base metal developed by same method_ The nanocomposites show superior machinability and tensile properties compared to the microcomposites and base metal.