Microstructure, Hardness and Chip Formation of an Aluminum Alloy Metal Matrix Composite Fabricated by Squeeze Casting Method

Abstract: Casting is the most economical route to transfer raw materials into readily usable components. However, Porosity in cast metal matrix composite (MMC) has been found as major cause of defect. Generally, increasing content of porosity will decrease the mechanical properties of MMC such as hardness, tensile strength, and damping capacity. Also casting results in variety of grain structure like dendrite structure, chilled grains, columnar grains and there is lack of expected homogeneity. On the contrary, forging process gives directional properties. The formation of a grain structure in forged parts is elongated in the required direction of the deformation. This structure gives better mechanical properties in the plane of maximum strain but lower across the thickness. The limitations of casting and forging can be eliminated in squeeze casting process where the force is applied on the alloy in between liquidous and solidus temperature. In squeeze casting, uniform and homogeneous grain structure is found which is favorable for machining. In this work, three specimens of alumnium metal matrix composite are prepared and examined for hardness, microstructure and pattern of chips while machining. Macro-examination of chips showed improved machinability and improved surface finish Hardness is increased with increase in reinforcement and squeezing.

Keywords: Aluminium alloy Metal Matrix Composite, Squeeze Casting, Microstructure, Hardness, Chips