Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/002—Castings of light metals
  • B22D21/007—Castings of light metals with low melting point, e.g. Al 659 degrees C, Mg 650 degrees C
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C3/00—Selection of compositions for coating the surfaces of moulds, cores, or patterns
• • 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

Definitions

• the invention relates to a method for casting aluminum alloys which contain more aluminum than the eutectic with the alloy partners, in order to achieve improved strength values by reducing the distances between the dendrite arm distances formed by solidification.
• the technological properties of the aluminum alloys in particular the strength, the yield strength and the elongation, can be improved by fine-grain of the casting.
• the strength properties of aluminum alloys are directly dependent on the number and fineness of the smallest possible dendrite arm distances - the secondary dendrite arm distances.
• the fine-grained nature of aluminum and aluminum-based alloys is improved by adding a pre-alloy to the aluminum alloy before casting, which can be used as heterogeneous nuclei e.g. Contains titanium diboride.
• the refractory material for dipping is added in the same way as in the abovementioned document as germs, noble metals or reducible metal oxides.
• the US-PS 3 157 926 works in the same way and names nickel-III-oxide, cobalt-II-oxide and -III-oxide and nickel-cobalt oxyhydrate as seeds.
• the seeds of the above-mentioned US patents are not effective for reducing the secondary dendrite arm spacings and thus for improving the strength properties of hypoeutectic aluminum alloys and are not proposed by the US patents. No corresponding seeds have been found for aluminum base melts, which are suitable for embedding in the mold wall to produce a fine-grained casting.
• DE-PS 963 642 teaches to influence the surface of castings by adding additives to the molding material and alloys the surface with lead released by chemical reaction with the casting metal.
• To avoid edge decarburization reducing protective substances are added to the molding material according to DE-AS 12 71 909, the melting point of which lies between the casting temperature and the firing temperature of the casting mold.
• DE-AS 12 65 356 discloses to add a hydrogen-releasing metal hydride to the casting mold in its mold cavity.
• the hydrogen is said to reduce the oxide skin of, for example, incoming iron as the casting material and thus increase the flowability.
• the aluminum oxide of the cast skin of aluminum cannot be reduced with hydrogen.
• the presence of hydrogen when casting aluminum alloys is also highly undesirable because gas bubbles form.
• German writings only disclose that the surface of the casting can be influenced by means of substances introduced into the mold.
• the problem of achieving improved fine grain, especially the reduced secondary dendrite arm Distances of hypoeutectic aluminum alloys are neither addressed, nor can it be solved with the measures mentioned therein.
• the object is achieved in a method of the type mentioned in that the inner wall of the mold is produced with numerous roughness in the micro range, that the inner wall is provided with a thin layer of a salt mixture, the cations of the salt mixture predominantly from those of the alkali and / or alkaline earth metals and their anions consist predominantly of those of the halogens, and that the liquidus temperature of the salt mixture is set lower than the casting temperature of the aluminum alloy.
• the transport of broken dendrite arms through the melt into central areas of the casting in addition to the growth of the fine dendritic solidification front, further improves the fine-grained interior or also areas of the mold inner wall that are not very effective, with a sufficient number of species Germs supplied.
• the salts whose cations predominantly consist of alkali and / or alkaline earth and whose anions consist predominantly of halogens reliably bring about a reduction in the dendrite arm distances.
• the invention can be advantageously configured as follows.
• the invention recommends producing as many as possible, but more than 10 5 roughnesses per cm 2 of the mold inner wall, the ratio of depth to diameter or depth to gap width of cracks being greater than 1 to 3.
• roughness in the form of pores, fracture edges, cracks and crevices, and preferably funnel-shaped depressions formed by sequences of microcrystalline fracture edges, which face the casting with the enlarging opening are recommended.
• Geometrically particularly favorable roughnesses are e.g. obtained by arranging a ceramic material which tends to break the shell in particularly finely ground grains with a diameter of predominantly less than 10 ⁇ m on the inner wall of the mold. This happens e.g. by "dipping", i.e. Dipping the wax model in a slip on an aqueous or alcoholic basis, which also contains a binder, e.g. based on silicon dioxide. It is also possible to use other ceramic powders which have suitable pore sizes and / or a suitable fine grain because of the way in which they are produced.
• the salt mixture contains one or more alkali and / or alkaline earth pseudohalogen compounds or else organic salts of the alkali and / or additionally contains alkaline earth metals
• Suitable alkali or alkaline earth pseudohalogen compounds are cyanate, cyanide, rhodanite, hexa- or tetracyano compounds, amines or amides or the like, the aikalicyanides, cyanates and rhodanides chemically related compounds.
• the removal of the oxygen residues is effective not only when cast in air, but also when cast in a vacuum at approx. 10 torr.
• these additional salts in about 2 to 40% by weight of the total salt mixture.
• the amount of salt added is expediently limited in such a way that the gas released during casting does not form bubbles on the surface of the casting, the released gas does not contain any molecular hydrogen and, furthermore, the salt is not stable under the pressure and temperature conditions of the preheating of the mold shell Has hydrates.
• the inner wall and its pore entrances can be provided with different salts simultaneously and in an even, finest distribution and also apply finely ground, slurried salts that are insoluble or insufficiently soluble to the inner wall.
• the intimate mixture of the various salts leads to rapid liquefaction.
• the preheating of the mold which takes place before the casting, in order to improve the flow of the casting, serves at the same time to dry the applied salts. Water and / or alcohol are suitable as solvents.
• salt mixture consisting predominantly of sodium-lithium chloride fluoride is used to coat the inner wall of the ceramic mold, the melting point of which is below 650 ° C., enables the salt mixture to be liquefied very quickly.
• these salt mixtures there are deep-melting mixtures of reciprocal salt pairs with low hydrostability of the individual salts, especially when compared to the salts of potassium.
• An aqueous and / or alcoholic solution of LiCl, NaF, NaC1 and Na 4 Fe (CN) 6 is particularly suitable. No premelting and grinding of the salt mixture is necessary.
• Sodium fluoride is water soluble. Due to ion exchange with the lithium chloride, fine-grained lithium fluoride precipitates after a few hours.
• the solution and / or slurry of the salt mixture contains a dispersing agent, fine-grained insoluble salts which separate out from the solution after some time, such as lithium fluoride, can be kept in suspension and a uniform distribution of the salt mixture on the inner wall of the mold can be promoted.
• Suitable dispersants are e.g. Methyl cellulose.
• Exemplary Embodiment 1 20 wax grapes were produced, each composed of eight tensile specimen models with an 8 mm diameter, the tensile specimens being arranged in a circle around a sprue and each having an annular top and bottom cut.
• the wax grapes were given a first coating by dipping into a slurry, consisting of an aqueous binder, finely ground zirconium silicate and silicon dioxide as filler, and sanded with coarse zirconium silicate powder. After drying, a further six layers were applied by dipping, sanding and drying in a conventional manner, so that ceramic shapes with wall thicknesses of approximately 8 mm were formed.
• the molds were waxed under pressure in an autoclave and then fired at approx. 800 ° C.
• the solution was poured into the ceramic molds one after the other, immediately poured out again and filtered in order to remove any ceramic granules that had been rinsed out.
• the ceramic molds were then heated to approx. 470 ° C, inserted into the vacuum casting machine when warm and at approx. 250 ° C mold temperature with the aluminum alloy GAISi7Mg0.6 at a melt temperature of 700 ° C, at 10-2 Torr filled.
• the aluminum melt was premelted in air, then degassed with a flushing gas mixture and then degassed in vacuo.
• the wax models of an aircraft structural part with an average wall thickness of 5 mm and at the nodes with a wall thickness of 15 mm were assembled into wax grapes according to the method described in exemplary embodiment 1, covered with the ceramic shell, waxed under pressure in the autoclave and then at approx. Fired at 800 ° C.
• the solution was poured into the ceramic molds one after the other, immediately poured out again and filtered in order to remove any ceramic granules that had been rinsed out.
• the ceramic molds were then heated to approx. 470 ° C, inserted into the vacuum casting machine when hot and at approx. 250 ° C mold temperature with the aluminum alloy GAISi7Mg0.6 at a melt temperature of 700 ° C, at 10 -2 Torr filled.
• the aluminum melt was premelted in air, then degassed with a purging gas mixture and subsequently degassed in vacuo.

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• 1985
  • 1985-04-03 DE DE19853512118 patent/DE3512118A1/de not_active Ceased
• 1986
  • 1986-03-26 IL IL78279A patent/IL78279A0/xx not_active IP Right Cessation
  • 1986-03-27 EP EP86104247A patent/EP0198290B1/fr not_active Expired - Lifetime
  • 1986-03-27 DE DE8686104247T patent/DE3671607D1/de not_active Expired - Fee Related
  • 1986-04-01 ZA ZA862393A patent/ZA862393B/xx unknown
  • 1986-04-02 BR BR8601478A patent/BR8601478A/pt not_active IP Right Cessation
  • 1986-04-02 JP JP61074397A patent/JPS61293653A/ja active Pending
  • 1986-04-02 SU SU864027428A patent/SU1760973A3/ru active
  • 1986-04-02 CA CA000505669A patent/CA1288210C/fr not_active Expired - Lifetime
  • 1986-04-03 ES ES553681A patent/ES8703097A1/es not_active Expired

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