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NOVEL METAL MATRIX COMPOSITES BASED ON HYPEREUTECTIC ALUMINIUM/SILICON-ALLOYS.

Objetivo

The aim is to develop a new family of MMCs based on A1/high Si alloys.
The feasibility of thixoforming has been shown as a means of achieving near net shapes in spray formed (and cast and extruded) aluminium silicon metal matrix composites (MMC). It has been demonstrated thet attention to alloy development to suit the thixoforming process, which has requirements different from those of casting or forging, can result in products of greater integrity. Some aspects of die design and materials development have also been studied, and these have indicated the routes to follow in order to further improve product consistency.

It has been confirmed that aluminium silicon MMCs with very high silicon loadings still possess all the properties for which the alloy system is renowned: high stiffness, wear resistance, fatigue life and hot strength, combined with low density and thermal expansion. Corrosion resistance is similar to that found in other copper containing aluminium alloys. Low ductility and fracture toughness will to some extent limit the range of applications for the MMC. The relative ease of recycling also deserves mention.

This work represents an important advance in processing and shaping what in many respects could be considered an intractable material. If aluminium silicon based MMCs are to achieve wider application then economic, clean and safe forming techniques need to be used. Thixoforming is just such a process.

Exploitation potential and anticipated benefits are best illustrated by consideration of the advantages which would accrue from the use of thixoformed hypereutectic aluminium silicon MMCs for internal combustion engine pistons. There would be a reduction in weight, allowing other components to be lighter as well. The closer match of thermal expansion coefficient to iron based piston rings would lead to greater fuel economy and less wear. Greater hot strength would allow higher operating temperatures and so less fuel consumption. Near net shaping by thixoforming and the fine silicon particles would simplify finishing operations.
Thixoforming is an inherently cleaner, safer and more energy efficient process.
The composites will consist of primary Si particles formed in situ in an A1/Si eutectic matrix, and will have enhanced specific stiffness, strength and wear resistance. In contrast with MMC systems such as A1/SiC, formed by mixing, there should be no brittle compounds at the matrix/particle interfaces. A fine, uniform distribution of primary Si will be obtained by spray-forming and preserved by semi-solid processing (thixoforming and thixocasting), which will result in near-net shape products.

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Coordinador

UNIVERSITY OF SHEFFIELD
Aportación de la UE
Sin datos
Dirección
WESTERN BANK
S10 2TN SHEFFIELD
Reino Unido

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Participantes (5)