Studies on Development of Magnesium Alloy AZ91D Si3N4 Metal Matrix Composites

Abstract

Today, world without materials cannot be imagined. Metal matrix composites are a significant newlinegroup of modern engineering materials that have clearly demonstrated their potential, as a newlinepromising material for various structural applications. The current trend is to work with light newlineweight composite materials which are easy to handle with minimised wear and tear during newlineassembly coupled with aesthetic appearance. The material selection criteria in a metal to newlinecomposite structure requires high specific strength, rigidity and good corrosion resistance along newlinewith minimum thermal expansion of the metal. newlineMagnesium - based materials are the lightest of all the light metals. It has a density of newline1.77g/cm3 newline. Its mass per volume range is 2/3rd of aluminum and 1/5th of steel. Among various newlinetypes of magnesium alloys, AZ91D magnesium alloy is the new age material, having a density newlineof 1.81 g/cm3 newline newline. AZ91D alloy possess outstanding properties such as excellent elastic modulus, newlinegood damping capacity, excellent weldability, coefficient of expansion, excellent newlinemachinability, and low density. newlineIt has been studied from various research work that AZ91D alloy cannot withstand resistance newlineto wear and corrosion at many applications, as it suffers from thermal instability and poor newlinehardness. However, there is a possibility of improving these properties by adding ceramic newlinematerials like silicon nitride as reinforcement. newlineSilicon Nitride ( Si3N4) possess high flexural strength, good fracture resistance, enhanced wear newlineresistance and excellent thermal properties in addition to low coefficient of friction as newlinecompared with other ceramics. It does not lose its characteristics even at wide range of newlinetemperatures.. These attractive properties have made them to be widely used as reinforcement newlineto develop light weight metal matrix composites. newlinePowder metallurgy technique is used to develop and synthesise AZ91D Mg-alloy with varying newlinevolume fractions of silicon nitride reinforcement. The developed composites were subjected to newlineball milling for few hours, compacted and sintered before sending the developed composites newlineto different tests. newline newlineStudies on Development of Magnesium Alloy AZ91D-Si3N4 Metal Matrix Composites newlineMechanical properties such as density, porosity, hardness, modulus, friction and wear and newlinethermal tests were conducted to analyse the behaviour of the AZ91D Mg-alloy and the newlinedeveloped composites. All the tests were conducted, by following ASTM standard test newlineprocedure. newlineA thorough investigation on the AZ91D Mg-alloy and the developed composites were newlineconducted. Microstructure studies revealed a fair distribution of the silicon nitride newlinereinforcement in to the AZ91D Mg-alloy and X-Ray Diffraction studies confirmed the presence newlineof silicon nitride on the AZ91D Mg-alloy. Density and porosity increased with an increase in newlinereinforcement content thus the hardness and the modulus of the composites, also increased. newlineAddition of Si3N4 particles decreased the coefficient of friction and wear rate of the developed newlinecomposite in comparison to the AZ91D Mg-alloy. With an increase in the reinforcement newlinecontent, thermal diffusivity decreased dramatically. Also the coefficient of thermal expansion newlinewas high when the silicon nitride content was increased, however it decreased when the applied newlinetemperature was decreased. newline