Authored by JO Hamed*
Abstract
This study has been designed to evaluate the surface roughness of an aluminum reinforced metal matrix composites produced by stir casting techniques at constant cutting speed of 1000 rpm, three (3) different feed rates at various aluminum weight ratio. Response surface methodology was adopted to formulate a surface roughness model in terms of metal matrix constituents such as aluminum, barite and zircon under three (3) different feed rate. The model adequacy was verified using analysis of variance. The increase in weight ratio of aluminum matrix reduces the surface roughness and vice versa. However, increase in barite, zircon weight ratios and feed rate increase the surface roughness. The F-values obtained at 95 % confidence interval revealed that the selected model adequately represent the data for the matrix composites. Therefore, the mathematical model developed is an effective tool for evaluating surface roughness.
Keywords: Surface roughness; Metal matrix; Composites; Feed rate; Stir casting
Introduction
In rocketry development, the temperature induced by the combustion process are of the order of 1000 °C to 3000 °C. However, when metals are continuously and plastically deformed at high temperature, both work hardening and annealing take place simultaneously, and creep in metals occur [1,2]. High temperature allows metal to deform more easily since atoms can move more freely, hence, greater movement of dislocations. Grain-boundary movement are also possible at higher temperatures [3]. Therefore, engineering alloys utilized at high temperatures is susceptible to creep as well as recrystallization and grain coarsening. In the case of age-hardened metals, over-ageing is feasible, which results in reduced hardness and strength due to the coarsening of the second phase precipitates. Furthermore, metals generally oxidize at high temperatures, thus experiencing creep problems [4].
Generally, The properties of a metal matrix such as high strength to-weight ratio, plasticity, capacity for crucial shape forming along with their ease for joining and good corrosion resistance have become increasingly focused for versatile applications such as design of armour structures, rocket, missile casing, light-weight defense vehicle, cars, and marine structures [5]. Also, varieties of metal matrix composites have been developed by manipulating the compositions and tailoring the fabrication technology to combats the inherent problem [6]. The requirements for producing high-quality matrix composites are inevitably associated with precision metal alloy design, innovative technology development in processing and enhancement of mechanical properties [7].
The development of an aluminum reinforced metal matrix composite is therefore a way to combat these problems and provide materials with enhanced mechanical properties. This is for example, the development of aluminum-barite-zircon matrix composites for aerospace and high-performance applications. Metal matrix composites (MMC) are new class of engineering materials which find its application in automotive, aircraft and defense mainly because of its improved property than alloys. There various matrix and reinforcement available out of which aluminum reinforced with ceramics particles finds to be important [8]. The particles are harder which improve the mechanical properties of the composites. The hard reinforcement makes the composites difficult to machine and get into required shape. Hence, the particles make the surface rough and increases tools wear. This discourage the use of metal matrix composite in many applications [9]. In order to overcome the difficulty, some amount of soft reinforcement material such as Barite, Zircon are added to form a hybrid MMC. The aluminumbarite- zircon MMC is easier to machine and shape into required specification [10].
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