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(11) | EP 0 501 539 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Metal matrix composite composition and method |
| (57) A method of making a new metal matrix composite material formed from an aluminium-based
alloy and a silicon carbide ceramic material is disclosed, in which preferably a porous
pre-form (20) of the silicon carbide ceramic material having SiO₂ on the surfaces
thereof is placed in an open-top die (24), heated to an elevated temperature in the
range of 399°C and 1093°C, and impregnated under pressure with a molten alloy (27)
comprising, by weight about 3 to 6 percent copper, about 0.5 to 5 percent magnesium
and the balance essentially aluminium. The silicon carbide pre-form (20) impregnated
with molten alloy is then cooled at a rate sufficient to sustain supersaturation of
the copper and magnesium in the aluminium down to a predetermined temperature. The
predetermined temperature is selected so as to permit precipitation in the alloy of
a strengthening copper-rich secondary metallic phase containing copper, magnesium
and aluminium and consisting essentially of about 40 to 80 percent by weight copper,
magnesium in an amount between about 5 and 30 percent by weight, and the balance essentially
aluminium. This results in the formation of a metal matrix composite material having
a silicon carbide phase, an aluminium-rich primary metallic phase and a copper-rich
secondary metallic phase which has the desired composition. The primary metallic phase
can contain up to 10 percent of eutectic phase which is generally present as a coarse
network or as isolated islands within the primary phase. Preferably, cooling occurs immediately after the impregnating step and relatively rapidly to a temperature below about 288°C, where precipitation of the secondary metallic phase occurs. Preferably, the secondary metallic phase comprises a cubically-shaped crystal structure which measures about 40 nanometres on a side. |