Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/23—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces involving a self-propagating high-temperature synthesis or reaction sintering step
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/20—Measures not previously mentioned for influencing the grain structure or texture; Selection of compositions therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • 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
  • C22C32/0047—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 carbides, nitrides, borides or silicides as the main non-metallic constituents
  • C22C32/0073—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 carbides, nitrides, borides or silicides as the main non-metallic constituents only borides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

• the present invention concerns a process for the preparation of a grain refiner contained within an aluminum matrix, to a grain refiner produced by said process and to the use thereof.
• the grain size is an important factor to control since it influences many mechanical and chemical properties of the cast material.
• the molten metal must have sufficient crystal nuclei to obtain the desired grain size of the cast products. It is often necessary to increase the number of crystal nuclei through additions to the melt. This is usually achieved by adding to the melt a master alloy containing a very large number of nucleating particles, which disperse in the aluminum melt.
• Titanium is the most common additive for grain refining of aluminum, and also a very efficient additive in this regard. At normal melting and casting temperatures, titanium concentrations above 0.2% (m/m) form with aluminum the intermetallic phase Al3Ti, although lower concentrations will also give a grain refining effect. In the production of a master alloy containing 1-15% Ti in aluminum, particles of Al3Ti form together with some Ti in the solution, in accordance with generally accepted phase diagrams. Also it is generally known that addition of boron to master alloys containing Ti will considerably improve the grain refining effect, especially when the Ti/B ratio is between 2.2 and 25.
• Object of the invention is to provide a process for the preparation of a grain refiner from relatively simple starting products, without the disadvantages of the prior art processes.
• the invention is based thereon that it has been found that an excellent grain refiner can be prepared by solid state reaction of a reaction product of titanium and aluminum and a reaction product of boron and aluminum contained within at least one aluminum matrix.
• the invention concerns a process for the preparation of a grain refiner contained within an aluminum matrix, comprising intimate mixing of at least one reaction product of titanium and aluminum contained within an aluminum matrix and of at least one reaction product of boron and aluminum contained within an aluminum matrix thereby obtaining solid state reaction products by reacting the reaction products by solid state reaction.
• the reaction product of titanium and aluminum contained within an aluminum matrix is preferably Al3Ti in aluminum, whereas the reaction product of boron and aluminum is preferably AlB2 and/or AlB12.
• AlB2 In view of reactivity and efficiency the use of AlB2 is preferred. However the presence of AlB12 in combination with AlB2 can also lead to a good grain refiner.
• the solid state reaction mentioned above is defined to cover a reaction process starting with joining and intimately mixing said solid reaction products, i.e. Al3Ti and AlB2 (and/or AlB12) both contained in an aluminium matrix, and leading to a certain amount of TiB2 besides a rest of only Al3Ti.
• said reaction products are reacting.
• said solid state reaction covers, at least partly dissolving of the reaction products to their separate components, physical diffusion of said components, and chemically reacting of Ti an B to TiB2 (or TiB12).
• the preparation of the reaction product of titanium and aluminum contained within an aluminum matrix and of the reaction product of boron and aluminum contained within an aluminum matrix can easily be done in a manner known in the art.
• the technique to be used can be the same as the technique for the preparation of Al/Ti and Al/B master alloys.
• the preparation is done by adding titanium containing raw materials (such as titanium sponge or titanium salts) and boron containing raw materials (such as boron salts) to molten aluminum.
• the titanium component, Al3Ti and the boron component, AlB2 and/or AlB12 are preferably used in the form of their alloys with aluminum, i.e. in the form of Al3Ti in aluminum and AlB2 and/or AlB12, in aluminum. These alloys are subsequently intimately mixed in the solid state during or after which the materials are heated to the temperature required for the solid state reaction.
• the intimate mixing can be carried out in different ways. According to one embodiment particles of the two materials, such as granules, powder, flakes, needles or likewise shaped fine particles are intimately mixed, followed by heating of the resulting mixture. This heating can take place by compacting or extruding the mixture with sufficient shear or force to cause the temperature to rise to the required level. It is however preferred to anneal the material after compacting or extruding as this gives a better control of the process and thus a more reproducible product. Another possibility is formed by the heating during extruding of the material.
• the materials are coextruded at a temperature below the melting point of the materials, optionally with heating. If necessary this process can be repeated a few times until sufficient mixing has been obtained. Depending on the temperature used the materials may have reacted, but generally it will be preferred to heat the mixture after mixing to let the materials react.
• the particle size and the state of the powders should be such as to promote solid state diffusion and reaction to occur.
• the particle sizes should not be too small, as this has been found to result in a less improved effectiveness, possibly due to a too high oxygen content caused by the higher surface area. Suitable particle sizes are thus between 50 ⁇ m and 1 mm.
• the heating or annealing of the materials should also be such that the solid state reaction as defined above can proceed to a suitable degree. Suitable temperatures are from 400 °C. An upper limit is formed by the melting temperature of the materials. The temperature also depends on the length of time, longer heating times requiring lower temperatures. The heating time usually ranges from 0.1 to 5 hours. Longer times do not provide any advantage, whereas the lower limit is generally necessary to obtain sufficient reaction.
• the amount of titanium in the grain refiner is preferably between 0.2 and 15% by weight, whereas the amount of boron in the grain refiner is preferably between 0.02 and 10% by weight.
• the ratio of titanium to boron (m/m) is between 1 and 80, more in particular between 2.5 and 35.
• the solid state reaction products containing said components at least comprise Al3Ti and TiB2, having particle sizes of up to 30 ⁇ m and up to 5 ⁇ m respectively.
• Preferred solid state reaction products contain fine and many phase particles. Preferred particle sizes are respectively 10-30 ⁇ m and 0.5-5 ⁇ m. Said component product particle sizes are determined microscopically, which means that at a particular size at least 80% of the particles observed will have said size.
• the grain refiner according to the invention can be used in various shapes, such as powder, needles, flakes, granules and the like.
• the grain refiner is produced in the shape of wire, as is conventional in the art of aluminum casting.
• the grain refiner can be used for preparing aluminum intermediate products, such as ingots, but it can also be used for the production of castings.
• the mixture of granules was first compacted to an extrusion billet and subsequently extruded.
• the extruded material was annealed at 640 °C for the time given in the table.
• the various products were tested for the grain refining response, i.e. the grain size (in ⁇ m) of the aluminum wherein the grain refiner has been included. Grain sizes are determined in accordance with the so-called Kawecki-Billiton grain refinement test, or ring test (see article by Vader et al., "Interrelations between aluminium grain refining by means of aluminium titanium boron alloys and the number of growth centers", Internationalechtmetalltagung, Leoben-Wien 1987, 22-26 June, 1987).
• a mixture of granules of a reaction product of titanium and aluminum contained within an aluminum matrix containing about 3.4% (m/m) of titanium in the form of Al3Ti, and of powder of a reaction product of boron and aluminum contained within an aluminum matrix having a boron content of 1.4% (m/m) was prepared.
• This mixture was subsequently compacted and multiply extruded into a wire and annealed at 640 °C.
• the compacted material was extruded five times, i.e. after extrusion the wire was cut into pieces of wire which were extruded again to obtain a wire of grain refiner.
• Table 4 The results of the grain refining response are given in Table 4.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)

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Cited By (8)

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Citations (3)

• 1991
  • 1991-07-05 GB GB919114586A patent/GB9114586D0/en active Pending
• 1992
  • 1992-07-02 EP EP92202013A patent/EP0521580A1/de not_active Withdrawn
  • 1992-07-03 JP JP4176870A patent/JPH05195108A/ja active Pending
  • 1992-07-03 AU AU19438/92A patent/AU1943892A/en not_active Abandoned
  • 1992-07-03 NO NO92922637A patent/NO922637L/no unknown
  • 1992-07-07 BR BR929202457A patent/BR9202457A/pt not_active Application Discontinuation

Patent Citations (3)

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