Friction properties of Al-1.5 Pct Mg/SiC particulate metal-matrix composites
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Friction Properties of A1-1.5 Pct Mg/SiC Particulate Metal-Matrix Composites FARID RANA and D.M. STEFANESCU With the advent of A1-SiC metal matrix composites (MMCs), research has been devoted to enhance the production, processing, and properties of these composites. u] The low cost of production of cast composites is an added benefit over other methods of production. By optimizing the dispersion of SiC particles in the matrix, conventionally cast products become comparably superior to other methods. Apart from providing higher strength materials, A1-SiC MMCs show comparatively superior wear-resistance and frictional properties. The specific properties of the reinforcement particle size, fractional content, and dispersion uniformity are particularly important in enhancing mechanical properties, pl Presently, aluminum alloys with SiC reinforced composites are being used extensively in tribological applications, such as pistons for internal combustion engines, pj Tribological properties include sliding wear friction, seizure resistance, and abrasive wear. I41 The determination of frictional properties of A1-SiC metal matrix composites for tribological use is essential at this point. Since previous work by Sato and Mehrabian f~j made no attempt to generate information relating weight percent and size of the nonmetallic particles to frictional properties, this paper discusses the method of measuring the coefficient of friction between the composite and tool steel base and aims to determine a relationship between the frictional properties and the weight percent, particle size, and dispersion of SiC particles. A1-1.5 pet Mg SiC cast metal matrix composites were prepared using conventional casting techniques. The SiC particles were added to a vigorously agitated melt. Mixing was done with the help of a two-blade paddle stirrer. Composites were cast into cylindrical steel molds 6.25 mm in diameter and 125 mm long. A regression analysis model was used to determine the optimum processing parameters necessary for good dispersion of the particles in the melt. Processing parameters used were high mixing time (three minutes) and mixing speed (1050 rpm) and low
mixing temperature (750 ~ and feed rate of particles (26 gm/min) for good dispersion. Figure 1 shows a typical microstructure of the cast AI-1.5 pct Mg 15 pct SiC composites. The friction test equipment was a pin and disc type, shown schematically in Figure 2. The composite samples were pins 5 mm in diameter and 35 mm long. No special heat treatment was given to the cast specimen. The samples were polished down to 600 grit emery paper. A load of 0.35 kg was used to load the pin against the flat tool steel base (disc) rotating at 40 rpm. Sliding velocities of 0.11 m / s and 0.21 m / s were used. Increase in sliding velocity was achieved by changing the rotations per minute (rpm). The friction force was measured by strain gages calibrated down to 1 x 10 - 3 kg. The nondimensional friction coefficient ( f ) was calculated using the following formula: f =
Average friction for
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