ANISOTROPIC WEAR OF PLANAR-RANDOM METAL MATRIX COMPOSITES WITH ZINC ALLOY MATRIX

The effect of varying amounts of sigma-alumina fibre on the wear behaviour of an aluminium-zinc alloy with 30% zinc and 2% copper has been investigated. Specimens were produced by infiltrating shaped "Saffil" fibre preforms with molten alloy to produce disc-shaped composite plates with volume fractions of fibre of 10%, 17% and 26%. Metallography showed that the fibres were oriented in a planar random arrangement in the composite plates. The pin-on-disc technique was used to assess the dry wear resistance and coefficient of friction of the composites over a range of loads and volume fractions of fibres. Testing was carried out with the wear surface set normal and parrellel to the surface of the plate in order to determine the effect of predominant fibre orientation on wear behaviour. The coefficients of friction of the composites were higher than that of the unreinforced matrix alloy, but for both orientations were almost independent of fibre content and load. In general the wear rate decreased with an increase in volume fraction of fibre and increased with increasing load; however, the fibre orientation had a marked effect on the wear rate and greatly reduced wear occurred when the majority of the short fibres were oriented with their long axes normal to the plane of wear. This effect was particularly marked at the higher loads.