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Metal Casting Technologies : June 2006
ABSTRACT iscontinuously reinforced aluminium alloy matrix composites are considered as potential engineering materials for various applications. Melt route was employed for preparing the composites. Silicon carbide (SiC) and aluminium oxide (Al2O3) particles were used as reinforcement particles. Melt stirring was carried out with a graphite stirrer. The melt was poured into a preheated metallic mould. The base metal was prepared under same condition for the comparison of properties. Properties like tensile strength, hardness, coefficient of thermal expansion (CTE) and fluidity were determined on aluminium matrix composite and the base matrix. The Al/SiC composite displayed increase in tensile strength and hardness compared to the base matrix. Fluidity of the MMC was reduced compared to the base matrix. Microelectronic packaging materials require lower CTE. The CTE value of aluminium composite was reduced. The silicon carbide % can be adjusted to vary the coefficient of thermal expansion of the composite. The Al/Al2O3 MMC is more wear resistant than the base matrix. 1. INTRODUCTION Composites can be divided into three groups - polymer matrix composites (PMC), metal matrix composites (MMC) and ceramic matrix composites (CMC). PMC use a polymer resin as the matrix and fibres like glass, carbon and aramid as the reinforcement. Metal matrix composites (MMC) are engineering materials in which a ceramic reinforcement is incorporated into a metal matrix to improve its properties. CMC materials use a ceramic as the matrix and reinforce it with fibres or whiskers. CMC and MMC are used in high temperature applications compared to PMC. CMC can stand much higher temperature than MMC. The commonly used reinforcements in MMC system are silicon carbide (SiC), aluminium oxide (Al2O3), Zircon, TiC, B4C, titanium diboride, mica and graphite. MMC reinforcements can be divided into continuous fibers, discontinuous fibers, whiskers and particulates. Fibre & whisker reinforced MMC are expensive compared to particulate reinforced MMC. Particulate-reinforced MMC can be fabricated with conventional metalworking equipment. Silicon carbide (SiC) is a popular ceramic reinforcement used in the MMC field. SiC particles are lower in cost and can be incorporated easily into Al and Mg alloy matrices. By varying the volume fraction of reinforcement, properties like coefficient of thermal expansion and thermal conductivity can be varied. The reinforcements increase the wear resistance of the alloys and minimize the coefficient of thermal expansion. The general matrices used in MMC area are aluminum/aluminium alloy, magnesium, zinc alloys, copper and titanium. Today's research and development in metal matrix composites are mostly based on aluminium and its alloys because aluminium is lighter and it is inexpensive in comparison with other metals such as titanium and magnesium. Also aluminum and it alloys are attractive due to their high thermal and electrical conductivities. In discontinuously reinforced aluminium composites, the aluminum matrix is reinforced with ceramic particles, whiskers, or short fibers. Aluminium matrix composite reinforced with SiC possess properties like improved strength, wear resistance and resistance to corrosion and has applications in automotive and aerospace industries1. The ceramic reinforcements used in metal matrix composites have smaller values of coefficient of thermal expansion (CTE) than the metal into which they are added. The addition of ceramic reinforcements to the metal like aluminium will result in reduction in the CTE value. MMC finds applications in thermal management and electronic packaging areas because coefficient of thermal expansion (CTE) of the MMC can be adjusted by varying the SiC % while maintaining the thermal conductivity2. The particle reinforced aluminium alloy composites can be produced by various fabrication processes like melt processing and powder metallurgy. METAL Casting Technologies June 2006 22 By Amit M Joshi Dept. of Metallurgical Engineering & Materials Science. Indian Institute of Technology -- Bombay, India. Email: firstname.lastname@example.org Preparation, Properties & Applications of Aluminium Matrix Composites Reinforced by Ceramic Particles