Fabrication of Metal Matrix Composite Automotive Parts

Driven by the need to build lighter weight, quieter and more fuel-efficient engines, the automotive industry has recognised the need for materials substitution, offering outstanding proper-ties in a number of engine components, including engine poppet valves. Since the valves control the gas flow, valve size, timing and overlap, they all influence volumetric efficiency. The valve train is designed to achieve maximum volumetric efficiency at the desired level of engine performance. Also engine valves are subjected to high operating temperatures and stress con-ditions which affect durability. The application of finite element analysis resulting in a Weibull failure theory analysis is a valid tool in predicting the probability of failure of the valves. The present work envisages carrying out some studies on Al-SiC and Al-TiC composites as possible alternative materials for engine poppet valves.

The present trend to make parts at or near net shape has brought powder metallurgy (PM) to the forefront and is being vigorously pursued by automotive design and materials engin-eers who are finding an increased application for this energy-and cost-saving process. Mixtures of four different compositions (15, 20, 25, 30% by weight) of SiC were prepared. By the PM technique, valves were fabricated by placing these powder mixtures in layers (one weight per cent along the stem and one along the base) in a die.

Specimens ( φ15 × 30) were also prepared by the PM technique so that properties like compressive, tensile strength, etc. could be studied. A die was fabricated to cast valves through a liquid metallurgy route.