Metal matrix composite

Details Metal matrix composite Metal matrix composite

1994-12-06

1996-06-25

Andrews, Melvyn

Alloys or metallic compositions

Aluminum base

Copper containing

C22C 2112

Patent

active

055297480

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to metal matrix composite materials and in particular to improvements in aluminium matrix alloys for such materials
Metal matrix composite materials comprising aluminium-copper-magnesium alloys which contain reinforcements of particulate silicon carbide are currently attracting a great deal of interest amongst aerospace manufacturers. Such materials have the potential to become widely adopted in applications where increased strength and stiffness are required in comparison to conventional aluminium alloys.
However, one of the drawbacks of metal matrix composite materials is that a sufficient quantity of the reinforcing material must be incorporated to achieve significant weight savings or improvements in performance. Addition on this scale is apt to have an adverse effect on certain properties, notably toughness and ductility. Moreover, known composite materials of this type often exhibit a rapid natural ageing response following solution heat treatment, with the result that difficulties are encountered when post-form stretching techniques are used to make extruded product forms or the like.
It is therefore an object of this invention to improve the fabricability of metal matrix composite materials. We have now discovered that the removal of magnesium from the matrix alloy of such materials leads to a surprising but significant improvement in fabricability. Metal matrix composites which use a magnesium-free matrix alloy are much easier to process and show a minimal natural ageing response over prolonged periods.
According to the invention there is provided a metal matrix composite material comprising from 1 to 50% by weight of reinforcing material embedded in an alloy matrix, characterised in that the alloy matrix has the following composition in proportions by weight: ##EQU1## wherein the alloy matrix further comprises one of the grain refining additives from the group comprising zirconium, manganese or chromium in an amount up to 0.5% by weight.
The matrix alloy preferably contains from 4-6% by weight of copper. Also, the proportion of grain refining additive is preferably from 0.05 to 0.2% by weight.
In a particularly preferred form, the weight proportion of the reinforcing material is from 10 to 30%, more preferably from 15 to 25% and most especially from 18 to 22%. Suitable materials for the reinforcement-include silicon carbide, alumina, boron, graphite, diamond and boron carbide. These may take the form particles, whiskers, short fibres or continuous fibres, depending upon the particular end use for which the composite material is intended.
The invention will now be described by way of example with reference to the drawings, in which:
FIG. 1 is a graph showing the effect of matrix alloy composition and natural ageing on the tensile properties of Al/Cu/Mg composites having 20% by weight of particulate SiC reinforcement;
FIG. 2 is a graph showing the effect of natural ageing on the tensile properties of a metal matrix composite according to the invention comprising an Al-4.35% Cu matrix containing by weight of particulate SiC reinforcement.
FIG. 3 is a graph showing the effect of matrix alloy composition and artificial ageing at 150.degree. C. on the tensile properties of composite materials corresponding to those used in FIG. 1, and
FIG. 4 is a graph showing the effect of artificial ageing at 150.degree. C. in metal matrix composites containing 20% by weight of particulate SiC reinforcement in matrix alloys according to the invention.
The test samples used to obtain the experimental results shown in these graphs were produced from material which had been manufactured by a powder metallurgy route to produce billets 125 mm long and 55 mm in diameter. The billets had a silicon carbide content of 20% by weight, a particulate silicon carbide being used with a mean particle size of 3 .mu.m.
The billets were vacuum degassed for 1 hour at temperatures between 450.degree. and 530.degree. C., followed by hot isostatic pressing within the same temperature range. A suitable pressure

REFERENCES:
patent: 4383970 (1983-05-01), Komuro et al.
patent: 4597792 (1986-07-01), Webster
patent: 4946647 (1990-08-01), Rohatgi et al.

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