Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals
  • C22C1/1036—Alloys containing non-metals starting from a melt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
  • C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
  • C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
  • C22C32/0036—Matrix based on Al, Mg, Be or alloys thereof

Definitions

• This invention relates to a method of making metal matrix composites where the metal is aluminium or an alloy thereof.
• Metal matrix composites comprising a refractory inorganic filler material such as silicon carbide or alumina in a matrix of aluminium or an alloy thereof are useful engineering materials, for example where high strength and low density are required as in the motor vehicle and aerospace industries.
• molten Al or Al alloy cannot wet the solid filler material sufficiently for such composites to be made satisfactorily by stirring the filler into the molten metal.
• the invention provides a method of making a solid composite material comprising a refractory, inorganic filler material in a matrix of aluminium or an aluminium-containing alloy such as an aluminium base alloy, which comprises
• the molten Al or alloy takes up at least twice the amount of filler by weight when the bismuth additive is present than when it is absent, and further that the filler is more uniformly dispersed in the matrix when a bismuth additive is used.
• the filler material may be a material known in the art for enhancing the properties of aluminium and aluminium base alloys.
• examples are refractory carbides such as silicon carbide and refractory oxides such as alumina.
• the bismuth additive is a bismuth compound such as bismuth oxide when the dispersion may be prepared in step (i) by intimately mixing fine particle elemental bismuth with particulate filler material, for example of particle size in the range of 5 ⁇ m to 100 ⁇ m wherein the weight of bismuth is preferably less than 10% of the weight of the filler, followed by oxidising the elemental bismuth to bismuth oxide (Bi2O3), e.g. by heating in air at 500°C to 1000°C. Heating in air causes the bismuth to burn and generate smoke thereby facilitating production of a fine oxide dispersion.
• oxidising the elemental bismuth to bismuth oxide e.g. by heating in air at 500°C to 1000°C. Heating in air causes the bismuth to burn and generate smoke thereby facilitating production of a fine oxide dispersion.
• step (i) it may however be possible to prepare the dispersion in step (i) in other ways, for example by mixing the filler material with an aqueous solution of a decomposable bismuth salt such as bismuth nitrate followed by heating to decompose the salt to bismuth oxide.
• a decomposable bismuth salt such as bismuth nitrate
• Step (ii) may be carried out by the known technique of vacuum stirring wherein the dispersion of step (i) is stirred into the molten aluminium or aluminium base alloy in vacuo.
• the aluminium or aluminium base alloy may be at a temperature considerably above its liquidus, for example at 150°C above its liquidus.
• bismuth compounds embrittle aluminium and aluminium base alloys at elevated temperature. It may, therefore, be necessary to add a material capable of reacting with surplus bismuth additive, i.e. a bismuth "getter", between steps (ii) and (iii). Examples of such getters are magnesium and manganese.
• a bismuth getter may not be necessary in all cases; for example, an aluminium base alloy, if used, may contain a getter as a component thereof and hence provide at sufficient quantity of the getter.
• the composite material produced in step (iii) may, for example, be pressure die cast, squeeze cast, chill cast or wrought.
• a shaped composite may be produced directly in step (iii) by cooling the product of step (ii) in a mould.
• the composite produced by this invention may have a range of compositions subject to product and/or processing requirements and restrictions.
• Step (ii) The above dispersion was stirred into an aluminium base alloy (LM6, containing ⁇ 10.5% Si) in vacuo for 2 hours in the temperature range of 740°C to 770°C.
• LM6 aluminium base alloy
• Step (iii) The molten product of step (ii) was cooled to the freezing point of the alloy in about half an hour.
• the alloy had taken up about 20% of its weight of alumina which was fairly uniformly distributed therein on a macro scale.
• the material was capable of being melted and chill cast and pressure die cast without undue difficulty.
• a sample of the material was heated to 850°C and poured through a 10 mm hole under a head of approximately 20 mm to show that it was sufficiently fluid when molten to be cast.
• the material was then heated to 850°C and cast into a cast iron mould. Sections of the resulting casting were examined microscopically where it was observed that the alumina filler material had been retained and that its distribution in the matrix was, if anything, more uniform than in the composite material product of step (iii).

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Compositions Of Oxide Ceramics (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=10589894

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• 1985
  • 1985-12-17 GB GB858531070A patent/GB8531070D0/en active Pending
• 1986
  • 1986-12-03 GB GB8628885A patent/GB2184133B/en not_active Expired
  • 1986-12-03 EP EP86309433A patent/EP0227352A3/fr not_active Ceased
  • 1986-12-10 JP JP61294601A patent/JPS62146229A/ja active Pending

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