CA1288210C - Process for casting aluminum alloys - Google Patents
Process for casting aluminum alloysInfo
- Publication number
- CA1288210C CA1288210C CA000505669A CA505669A CA1288210C CA 1288210 C CA1288210 C CA 1288210C CA 000505669 A CA000505669 A CA 000505669A CA 505669 A CA505669 A CA 505669A CA 1288210 C CA1288210 C CA 1288210C
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- Prior art keywords
- casting
- wall
- mold
- salt mixture
- process according
- Prior art date
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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
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Mold Materials And Core Materials (AREA)
Abstract
PROCESS FOR CASTING ALUMINUM ALLOYS
ABSTRACT OF THE DISCLOSURE
The technical properties of aluminum alloys, particularly tensile strength, yield strength and elongation percent, can be improved by refining the grain of the casting. For that purpose, particular attention must be paid to obtaining the smallest possible intervals between the second-ary dendrite arms. Seeding the melt by adding seeds with a pre-alloy does not bring satisfactory results, particularly with respect to the dendrite arm intervals. Small dendrite arm intervals and good technical values can be reliably obtained by casting the aluminum alloys in a ceramic mold with numerous micro-sized rough spots and pores and applying to the inner wall of the mold after it is dried and fired a thin layer of a salt mixture in which the cations are primarily from alkalis and/or alkaline earths and the anions are primarily from halogens and which has a liquidus temperature lower than the casting temperature of the alloy.
ABSTRACT OF THE DISCLOSURE
The technical properties of aluminum alloys, particularly tensile strength, yield strength and elongation percent, can be improved by refining the grain of the casting. For that purpose, particular attention must be paid to obtaining the smallest possible intervals between the second-ary dendrite arms. Seeding the melt by adding seeds with a pre-alloy does not bring satisfactory results, particularly with respect to the dendrite arm intervals. Small dendrite arm intervals and good technical values can be reliably obtained by casting the aluminum alloys in a ceramic mold with numerous micro-sized rough spots and pores and applying to the inner wall of the mold after it is dried and fired a thin layer of a salt mixture in which the cations are primarily from alkalis and/or alkaline earths and the anions are primarily from halogens and which has a liquidus temperature lower than the casting temperature of the alloy.
Description
PROCESS FOR CASTING_ALUMINUM ALLOYS 18,724 FIELD AND BACKGROUND OF THE INVENTION
This invention relates in general to aluminum alloys and in particular to a new and useful process for casting aluminum alloys.
The invention relates particularly to a process for casting aluminum alloys that contain mo e aluminum than corresponds to the eutectic with the other alloy constituents in order to achieve better strength values by reducing the spacing of the intervals between the secondary dendrite arms created upon solidification.
It is known that the technical properties of aluminum alloys, particularly tensile strength, yield strength and elongation percent, can be improved by refining the grain of the casting. It is known that the strength properties of aluminum alloys are directly related to the number and fineness of the smallest possible dendrite arm intervals, the secondary dendrite arm intervals. According to Foundry, June 1963, pp. 78-82, the grain fineness of aluminum and aluminum-base alloys is improved by adding a pre-alloy to the aluminum alloy before casting that contains titanium diboride, for example, as heterogeneous seeds.
From U.S. Patent 3,259,948, it is known that the grain fine-ness of castings of co~alt-or nickel-base alloys can be . ~ -fi~
improved by introducing seeds onto the inner surface of the casting mold. These seeds, e.g., cobalt aluminate and cobalt silicate, are applied pursuant to the U.S. patent, to the wax pattern and partly embedded in the inner surface of the mold by then dipping the wax pattern in a slip of refractory mold material (dipping) and melting away the wax pattern.
According to U.S. patent 3,019,497, seeds, again for the purpose of grain refinement, are mixed with the refractory material for dipping and appliedto the wax pattern. According to U.S. patent 3,158,912, precious metals or reducible metallic oxides are added as seeds to the refractory material ~or dipping in the same manner as in the other patent mentioned.
U.S. patent 3,157,926 works the same way and ment.ons nickel (III) oxide, cobalt (II) oxide and (III) oxide and nickel-cobalt hydroxide as the seeds. The seeds used in the above-mentioned U.S. patents are not effective in and are not proposed by the U.S. patents for reducing the secondary dendrite arm intervals and hence for improving the strength properties of hypo-eutectic aluminum alloys. For aluminum-base melts there are still no corresponding seeds that aresuitable for embedding in the wall of the mold in order to produce a fine-grained casting. According to FoundrY 1963, the grain fineness of aluminum alloys is improved by adding seeds with the pre-alloy. This is unsatisfactory, however, in terms of reliability and obtaining the smallest possible secondary dendrite arm interval. German patent 963,642 teaches influencing the surface of the casting by means of additives to the mold material and alloys the surface with lead released by chemical reaction with the casting metal.
30 In order to avoid decarbonization of the skin, according to German patent 12 71 909, protective materials to reduce the mold material are added that have melting points that lie between the casting temperature and the firing temperature of the casting mold. German patent 12 65 356 discloses a method 35 whereby the cavity of the mold is treated with a metallic hydride that releases hydrogen. The hydrogen is intended to reduce the oxide skin of the entering casting mterial, iron, ~or example, and thus increase flowability. It is known that the aluminum oxide of the cast skin of aluminum is not re-ducible by hydrogen. Furthermore, the presence of hydrogen during the casting of aluminum alloys is highly undesirable since it can cause the creation of gas bubbles.
The above mentioned German patents teach only that one can have an effect on the surface of the casting with the aid of substances introduced into the mold. The problem of achieving better grain refinement, particularly smaller secondary dendrite arm intervalsin hypo-eutectic aluminum alloys is neither discussed nor solvable by the measure mentioned therein.
SUMMARY OF THE INVENTION
The invention provides a process to improve substantially grain fineness and in particular the reliability with which it can be adjusted. In accordance with the invention, the inner wall of the casting mold is made with numerous micro-sized rough spots and the inner wall is provided with a thin layer of a salt mixture. The cations of the salt mixture consist largely of an alkali metal and/~or an alkaline earth metal and the anions consist largely of anions of the halogens, and the liquidus temperature of the salt mixture is set lower than the casting temperature of the aluminum alloy.
Using this process, substantially higher values for strength and elongation were achieved than with the prior art processes.
In the applicant's opinion, this is due to the fact that with the process pursuant to the invention, the metal melt, with the help of the salt mixture, which after the metal melt i8 poured should be as fluid as possible, fills in even the smallest pores and other rough spots on the inner wall of the mold shell. The metal cools there first and solidifies, so that many crystallization centers stand in a favorable crystalline orientation to the still liquid casting in the direction of heat elimination already predetermined by the geometry of the mold shell and can act as characteristic seeds. In addition,grain fineness in the interior is surely further improved by movement of broken-off dendrite arms throug~ the melt into the central areas of the casting in addition to the advancing growth of the fine dendritic ~alidification front, or even areas of the inner wall of the mold that are relatively ineffective will be supplied with 1~ a sufficient number of characteristic seeds. The fact that the ceramic mold with rough spots and pores is provided after dryi-ng and firing with the thin salt layer, which has a liquidus temperature lower than the casting temperature of the alloy, means that the salt mixture, being a thin, film-like layer that liquifies when the alloy is poured in, canspread out evenly even into the recesses of the rough spots and because of the thinness of the layer does not prevent the poured-in aluminum from penetrating into the pores. The salts, whose cations are largely from alkalis and/or alkaline earths and whose anions are primarily from halogens, reliably bring about a reduction in the dendrite arm spacing, according to the tests run by the applicant.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In greater detail, this is how that invention may be advant-ageously put to use:
When casting aluminum, in order to achieve the smallest possible supercooling spacing tlpon solidification, one requires crystallization centers with diameters on the order of from ten to several hundred angstrom units, which means that the geometry of the rough spots assume special significance. For this purpose, the invention recommends that as many as possible, but at any rate more than 105 rough spots be created per cm2 of the mold's inner wall, with a depth to diameter or depth to fissure width ratio greater than 1 to 3. Recommended are rough spots in the form of pores, faults, fissures and cracks as w-el-i~~s pre~erab~y ~unnel-shaped recesses, formed as a result of micro-crystalline faults, that have their larger opening towards the casting.
Rough spots that are particularly advantageous from a geomet-rical standpoint can be obtained by applying a ceramic material, for example, that has a tendency to conchoidal fracturing, in the form of p~rticularly fine-ground grains mostly less than 10 _~m in diameter to the inner wall of the mold. This is done by "dipping" for example, i.e., dipping the wax pattern in a slip with a water or alcohol base that also contains a binder with a silicon dioxide base, for example. Other ceramic powders may also be used that already have an appropriate pore size and/or an appropriate grain fineness as a result of their method of production.
By including in the salt mixture one or more alkali and/or alkaline earth pseudo-halogen compounds or even organic salts of alkali metals and/or alkaline earth metals, better removal of oxygen residues, particularly in the pores of the mold, can be achieved. Appropriate alkali or alkaline earth pseudo-halogen compounds are cyanate, cyanide, thiocyanate,hexa- or tetracyano compounds, amines or amides or similar compounds related to the akali cyanides, cyanates and thicyanides. The .. . . . . ..
removal of the oxygen residues works not only for casting in air, but also for casting in a vacuum at about 10 2 torr.
For this purpose it is advantageous to add these additional salts so that they constitute approximately 2 - 40% by weight of the total salt mixture. It is helpful if the salt admixture is limited in quantity so that it does not cause the gas released upon casting to create bubbles in the surface of the casting piece, if the released gas contains no molecular hydrogen, and further if the salt has no stable 10 hydrates under the pressure and temperature conditions that prevail in the pre-heating of the mold shell.
By applying the salt mixture in the form of a solution and/or finely dispersed slurry to the inner wall of the fired mold by pouring it in and out of the mold and subsequently drying it, one can provide the inner wall and its pore openings wit-h different salts at the same time and with ultra-fine, uniform distribution, and furthermore apply to the inner wall extremely finely ground salts in slurry fo~m that are insoluble or not readily soluble. At casting temperature, the intimate 20 mixture of the various salts liquifies quickly. The pre-heating of the mold prior to casting to improve the flow of the casting material serves at the same time as a means of drying the applied salts. Water and/or alcohol are suitable solvents.
If one uses a salt mixture to coat the inner wall of the 25 ceramic mold that consists primarily of sodium-lithium-chloride-fluoride with melting points below 650C, the salt mixturecan be liquified very quickly. These salt mixtures contain low melting mixtures of reciprocal pairs of salts with individual salts of low hydrostability,. particularly 30 in comparison with the potassium salts.
Particularly suitable is an aqueous and/or alcohol solution of .. . . . . . ...
s~
LiCl, NaF, NaCl and Na4Fe (CN)6. With this solution, no pre-melting and ~rinding ofthe salt mixture is required.
Sodium fluoride is water-soluble. By an exchange of ions with the lithium chloride, fine-grained lithium fluoride precipitates out within a few hours.
By including a dispersing agent in the salt mixture solution and/or slurry, fine-grained, isoluble salts that precipitate out of the solution after a certian time like the lithium fluoride can be held in suspension, thus facilitating uniform distribution of the salt mixture over the inner wall of the mold. A suitable dispersing agent is methyl cellulose, for example.
It also facilitates uniform distribution of the salt mixture upon drying to add to the salt mixture solution and/or slur y an auxiliary agent such as a surfactant that improves wetting of the inner wall of the ceramic mold.
The invention will now be explained on the basis of various concrete examples:
Experiments showed that the secondary dendrite arm intervals were approximately 40 - 50~um, while in the case of material treated according to the state of the art with a titanium diboride pre-alloy under the same casting conditions the intervals were approximately 80 - 90_1m.
20 wax clusters were produced, each composed of eight tensile test patterns 8 mm in diameter, with the tensile test patterns arranged in a circle around a pour funnel and each provided with a ring-shaped gate.
f i(~
The wa~ clusters were covered with a first coat by dipping in a slurry consisting of an aqueous binder and fine-ground (~ 30 ~um~ zirconium silicate and silicon dioxide as fillers and sanded with a coarse zirconium silicate powder. After drying, another six layers were applied by dipping, sanding and drying in conventional fashion, so that ceramic molds with walls about 8 mm thick were created. The molds were de-waxed under pressure in the autoclave and then fired at about 800C.
An aqueous solution of 20 g of LiCl, 20 g of NaF, 5 g of N4FE (CN)6,, 40 g of NaCl, 1 g of methyl cellulose and 0.1 g of surfactant per liter was then applied.
The solution was poured into the ceramic molds one after the other,immediately run off again, and filtered to remove any washed out ceramic grains.
The ceramic molds were then heated to approximately 470C, placed in a vacuum casting unit while still hot and at approximately 250C mold temperature filled with the aluminum alloy GAlSi7Mg 0.6 at a melt temperature of 700DC at 10 2torr.
The aluminum melt was premelted in air,then degassed with a scavenging gas mixture and re-degassed in a vacuum.
After conventional heat treatment, which included solution heat treatment and age hardening, the following strength values were obtained with little variation.
25 Tensile strength Rm ~ 340 N/mm2 Yield Strength Rpo > 280 N/mm2 Elongation percent A5 > 6.5%
. . .
t~
9_ Example 2 Wax patterns of a structural aircraft part with an average wall thickness of S mm and a wall thickness at the junction points of 15 mm were assembled into was clusters according to the method described in Example l, coated with the ceramic lining, de-waxed under pressure in the autoclave and then fired at approximately 800C.
An aqueous solution of 20 g of LiCl, 20 g of NaF, 5 g of Na4Fe (CN)6, 40 g of NaCl, l g of methyl cellulose and 0.1 g of lO surfactant per liter was then applied.
The solution was poured into the cermaic molds one after the other, imm~diately run off again and filtered in order to remove any washed out ceramic grains.
The ceramic molds were then heated to approximately 470C, 15 placed in the vacuum casting unit`while still hot, and at a mold temperature of approximately 250C willed with the aluminum alloy GAlSi7~g 0.6 at a melt temperature of 700C at lO 2 torr.
The aluminum melt was melted in air, degassed with a scavenging gas mixture, then re-degassed in a vacuum.
20 Following the heat treatment, whih included solution heat treatment and age hardening, the following strength values with little variation were found in surface tests from the precision casting portion:
Tensile strength Rm 350 to360 N/mm2 25 Yield strength Rp 0.2 290 to 310 Nlmm2 Elongation percent A5 to to 7%
, _ :
.
When the same melt was cast in a conventional mold without us.ing the steps specified by the invention, the following values were obtained;
Tensile strength Rm 300 N/mm2 Yield strength Rp 0.2 200 N/mm2 Elongation percent A5 3%
The technical values for tensile strength, ,yield strength and elongation percent were thus substantially improved by the use of the invention.
. , , . .. . ~ ~ . .
This invention relates in general to aluminum alloys and in particular to a new and useful process for casting aluminum alloys.
The invention relates particularly to a process for casting aluminum alloys that contain mo e aluminum than corresponds to the eutectic with the other alloy constituents in order to achieve better strength values by reducing the spacing of the intervals between the secondary dendrite arms created upon solidification.
It is known that the technical properties of aluminum alloys, particularly tensile strength, yield strength and elongation percent, can be improved by refining the grain of the casting. It is known that the strength properties of aluminum alloys are directly related to the number and fineness of the smallest possible dendrite arm intervals, the secondary dendrite arm intervals. According to Foundry, June 1963, pp. 78-82, the grain fineness of aluminum and aluminum-base alloys is improved by adding a pre-alloy to the aluminum alloy before casting that contains titanium diboride, for example, as heterogeneous seeds.
From U.S. Patent 3,259,948, it is known that the grain fine-ness of castings of co~alt-or nickel-base alloys can be . ~ -fi~
improved by introducing seeds onto the inner surface of the casting mold. These seeds, e.g., cobalt aluminate and cobalt silicate, are applied pursuant to the U.S. patent, to the wax pattern and partly embedded in the inner surface of the mold by then dipping the wax pattern in a slip of refractory mold material (dipping) and melting away the wax pattern.
According to U.S. patent 3,019,497, seeds, again for the purpose of grain refinement, are mixed with the refractory material for dipping and appliedto the wax pattern. According to U.S. patent 3,158,912, precious metals or reducible metallic oxides are added as seeds to the refractory material ~or dipping in the same manner as in the other patent mentioned.
U.S. patent 3,157,926 works the same way and ment.ons nickel (III) oxide, cobalt (II) oxide and (III) oxide and nickel-cobalt hydroxide as the seeds. The seeds used in the above-mentioned U.S. patents are not effective in and are not proposed by the U.S. patents for reducing the secondary dendrite arm intervals and hence for improving the strength properties of hypo-eutectic aluminum alloys. For aluminum-base melts there are still no corresponding seeds that aresuitable for embedding in the wall of the mold in order to produce a fine-grained casting. According to FoundrY 1963, the grain fineness of aluminum alloys is improved by adding seeds with the pre-alloy. This is unsatisfactory, however, in terms of reliability and obtaining the smallest possible secondary dendrite arm interval. German patent 963,642 teaches influencing the surface of the casting by means of additives to the mold material and alloys the surface with lead released by chemical reaction with the casting metal.
30 In order to avoid decarbonization of the skin, according to German patent 12 71 909, protective materials to reduce the mold material are added that have melting points that lie between the casting temperature and the firing temperature of the casting mold. German patent 12 65 356 discloses a method 35 whereby the cavity of the mold is treated with a metallic hydride that releases hydrogen. The hydrogen is intended to reduce the oxide skin of the entering casting mterial, iron, ~or example, and thus increase flowability. It is known that the aluminum oxide of the cast skin of aluminum is not re-ducible by hydrogen. Furthermore, the presence of hydrogen during the casting of aluminum alloys is highly undesirable since it can cause the creation of gas bubbles.
The above mentioned German patents teach only that one can have an effect on the surface of the casting with the aid of substances introduced into the mold. The problem of achieving better grain refinement, particularly smaller secondary dendrite arm intervalsin hypo-eutectic aluminum alloys is neither discussed nor solvable by the measure mentioned therein.
SUMMARY OF THE INVENTION
The invention provides a process to improve substantially grain fineness and in particular the reliability with which it can be adjusted. In accordance with the invention, the inner wall of the casting mold is made with numerous micro-sized rough spots and the inner wall is provided with a thin layer of a salt mixture. The cations of the salt mixture consist largely of an alkali metal and/~or an alkaline earth metal and the anions consist largely of anions of the halogens, and the liquidus temperature of the salt mixture is set lower than the casting temperature of the aluminum alloy.
Using this process, substantially higher values for strength and elongation were achieved than with the prior art processes.
In the applicant's opinion, this is due to the fact that with the process pursuant to the invention, the metal melt, with the help of the salt mixture, which after the metal melt i8 poured should be as fluid as possible, fills in even the smallest pores and other rough spots on the inner wall of the mold shell. The metal cools there first and solidifies, so that many crystallization centers stand in a favorable crystalline orientation to the still liquid casting in the direction of heat elimination already predetermined by the geometry of the mold shell and can act as characteristic seeds. In addition,grain fineness in the interior is surely further improved by movement of broken-off dendrite arms throug~ the melt into the central areas of the casting in addition to the advancing growth of the fine dendritic ~alidification front, or even areas of the inner wall of the mold that are relatively ineffective will be supplied with 1~ a sufficient number of characteristic seeds. The fact that the ceramic mold with rough spots and pores is provided after dryi-ng and firing with the thin salt layer, which has a liquidus temperature lower than the casting temperature of the alloy, means that the salt mixture, being a thin, film-like layer that liquifies when the alloy is poured in, canspread out evenly even into the recesses of the rough spots and because of the thinness of the layer does not prevent the poured-in aluminum from penetrating into the pores. The salts, whose cations are largely from alkalis and/or alkaline earths and whose anions are primarily from halogens, reliably bring about a reduction in the dendrite arm spacing, according to the tests run by the applicant.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In greater detail, this is how that invention may be advant-ageously put to use:
When casting aluminum, in order to achieve the smallest possible supercooling spacing tlpon solidification, one requires crystallization centers with diameters on the order of from ten to several hundred angstrom units, which means that the geometry of the rough spots assume special significance. For this purpose, the invention recommends that as many as possible, but at any rate more than 105 rough spots be created per cm2 of the mold's inner wall, with a depth to diameter or depth to fissure width ratio greater than 1 to 3. Recommended are rough spots in the form of pores, faults, fissures and cracks as w-el-i~~s pre~erab~y ~unnel-shaped recesses, formed as a result of micro-crystalline faults, that have their larger opening towards the casting.
Rough spots that are particularly advantageous from a geomet-rical standpoint can be obtained by applying a ceramic material, for example, that has a tendency to conchoidal fracturing, in the form of p~rticularly fine-ground grains mostly less than 10 _~m in diameter to the inner wall of the mold. This is done by "dipping" for example, i.e., dipping the wax pattern in a slip with a water or alcohol base that also contains a binder with a silicon dioxide base, for example. Other ceramic powders may also be used that already have an appropriate pore size and/or an appropriate grain fineness as a result of their method of production.
By including in the salt mixture one or more alkali and/or alkaline earth pseudo-halogen compounds or even organic salts of alkali metals and/or alkaline earth metals, better removal of oxygen residues, particularly in the pores of the mold, can be achieved. Appropriate alkali or alkaline earth pseudo-halogen compounds are cyanate, cyanide, thiocyanate,hexa- or tetracyano compounds, amines or amides or similar compounds related to the akali cyanides, cyanates and thicyanides. The .. . . . . ..
removal of the oxygen residues works not only for casting in air, but also for casting in a vacuum at about 10 2 torr.
For this purpose it is advantageous to add these additional salts so that they constitute approximately 2 - 40% by weight of the total salt mixture. It is helpful if the salt admixture is limited in quantity so that it does not cause the gas released upon casting to create bubbles in the surface of the casting piece, if the released gas contains no molecular hydrogen, and further if the salt has no stable 10 hydrates under the pressure and temperature conditions that prevail in the pre-heating of the mold shell.
By applying the salt mixture in the form of a solution and/or finely dispersed slurry to the inner wall of the fired mold by pouring it in and out of the mold and subsequently drying it, one can provide the inner wall and its pore openings wit-h different salts at the same time and with ultra-fine, uniform distribution, and furthermore apply to the inner wall extremely finely ground salts in slurry fo~m that are insoluble or not readily soluble. At casting temperature, the intimate 20 mixture of the various salts liquifies quickly. The pre-heating of the mold prior to casting to improve the flow of the casting material serves at the same time as a means of drying the applied salts. Water and/or alcohol are suitable solvents.
If one uses a salt mixture to coat the inner wall of the 25 ceramic mold that consists primarily of sodium-lithium-chloride-fluoride with melting points below 650C, the salt mixturecan be liquified very quickly. These salt mixtures contain low melting mixtures of reciprocal pairs of salts with individual salts of low hydrostability,. particularly 30 in comparison with the potassium salts.
Particularly suitable is an aqueous and/or alcohol solution of .. . . . . . ...
s~
LiCl, NaF, NaCl and Na4Fe (CN)6. With this solution, no pre-melting and ~rinding ofthe salt mixture is required.
Sodium fluoride is water-soluble. By an exchange of ions with the lithium chloride, fine-grained lithium fluoride precipitates out within a few hours.
By including a dispersing agent in the salt mixture solution and/or slurry, fine-grained, isoluble salts that precipitate out of the solution after a certian time like the lithium fluoride can be held in suspension, thus facilitating uniform distribution of the salt mixture over the inner wall of the mold. A suitable dispersing agent is methyl cellulose, for example.
It also facilitates uniform distribution of the salt mixture upon drying to add to the salt mixture solution and/or slur y an auxiliary agent such as a surfactant that improves wetting of the inner wall of the ceramic mold.
The invention will now be explained on the basis of various concrete examples:
Experiments showed that the secondary dendrite arm intervals were approximately 40 - 50~um, while in the case of material treated according to the state of the art with a titanium diboride pre-alloy under the same casting conditions the intervals were approximately 80 - 90_1m.
20 wax clusters were produced, each composed of eight tensile test patterns 8 mm in diameter, with the tensile test patterns arranged in a circle around a pour funnel and each provided with a ring-shaped gate.
f i(~
The wa~ clusters were covered with a first coat by dipping in a slurry consisting of an aqueous binder and fine-ground (~ 30 ~um~ zirconium silicate and silicon dioxide as fillers and sanded with a coarse zirconium silicate powder. After drying, another six layers were applied by dipping, sanding and drying in conventional fashion, so that ceramic molds with walls about 8 mm thick were created. The molds were de-waxed under pressure in the autoclave and then fired at about 800C.
An aqueous solution of 20 g of LiCl, 20 g of NaF, 5 g of N4FE (CN)6,, 40 g of NaCl, 1 g of methyl cellulose and 0.1 g of surfactant per liter was then applied.
The solution was poured into the ceramic molds one after the other,immediately run off again, and filtered to remove any washed out ceramic grains.
The ceramic molds were then heated to approximately 470C, placed in a vacuum casting unit while still hot and at approximately 250C mold temperature filled with the aluminum alloy GAlSi7Mg 0.6 at a melt temperature of 700DC at 10 2torr.
The aluminum melt was premelted in air,then degassed with a scavenging gas mixture and re-degassed in a vacuum.
After conventional heat treatment, which included solution heat treatment and age hardening, the following strength values were obtained with little variation.
25 Tensile strength Rm ~ 340 N/mm2 Yield Strength Rpo > 280 N/mm2 Elongation percent A5 > 6.5%
. . .
t~
9_ Example 2 Wax patterns of a structural aircraft part with an average wall thickness of S mm and a wall thickness at the junction points of 15 mm were assembled into was clusters according to the method described in Example l, coated with the ceramic lining, de-waxed under pressure in the autoclave and then fired at approximately 800C.
An aqueous solution of 20 g of LiCl, 20 g of NaF, 5 g of Na4Fe (CN)6, 40 g of NaCl, l g of methyl cellulose and 0.1 g of lO surfactant per liter was then applied.
The solution was poured into the cermaic molds one after the other, imm~diately run off again and filtered in order to remove any washed out ceramic grains.
The ceramic molds were then heated to approximately 470C, 15 placed in the vacuum casting unit`while still hot, and at a mold temperature of approximately 250C willed with the aluminum alloy GAlSi7~g 0.6 at a melt temperature of 700C at lO 2 torr.
The aluminum melt was melted in air, degassed with a scavenging gas mixture, then re-degassed in a vacuum.
20 Following the heat treatment, whih included solution heat treatment and age hardening, the following strength values with little variation were found in surface tests from the precision casting portion:
Tensile strength Rm 350 to360 N/mm2 25 Yield strength Rp 0.2 290 to 310 Nlmm2 Elongation percent A5 to to 7%
, _ :
.
When the same melt was cast in a conventional mold without us.ing the steps specified by the invention, the following values were obtained;
Tensile strength Rm 300 N/mm2 Yield strength Rp 0.2 200 N/mm2 Elongation percent A5 3%
The technical values for tensile strength, ,yield strength and elongation percent were thus substantially improved by the use of the invention.
. , , . .. . ~ ~ . .
Claims (11)
1. A process for casting aluminum alloys in a casting mold having an inner wall that contains more aluminum than corres-ponds to the eutectic with other alloy constituents in order to achieve better strength values by reducing the spacing of the intervals between the secondary dendrite arms created upon solidification, comprising providing an inner wall of a casting mold with numerous micro-sized rough spots, adding a thin layer of a salt mixture to the inner wall in which cations of the salt mixture comprise substantially an alkali metal and alkaline earth metal and the anions comprise substantially anions of halogens, and setting the liquidus temperature of the salt mixture lower than the casting temperatue of the aluminum alloy.
2. Process according to claim 1, wherein the inner wall of the casting mold has more than 105rough spots per cm2 with a depth to diameter or depth to fissure width ratio greater than 1 to 3.
3. Process according to claim 2, including an inner casting mold and wherein said inner wall comprises refractory material constituting the inner wall of the casting mold is made out of an extremely fine-grained oxide powder, obtained by grinding, and is produced by dipping a wax pattern in a slurry consisting of the oxide powder, a filler and a binder, then drying and firing it, whereby an oxide ceramic bond is created by the binder.
4. Process according to claim 1, wherein the salt mixture used also contains at least one alkali and alkaline earth pseudo-halogen compounds in the form of cyanate, cyanide, thiocyanate, hexa-and tetracyano compounds, amines or amides and similar compounds related to the alkali cyanides, cyanates thiocyanates and/or organic salts and/or metallic organic compounds of the alkali and alkaline earth metals.
5. Process according to claim 1, wherein the salt mixture used to coat the inner wall of the ceramic mold consists primarily of sodium-lithium-chloride-fluoride, with melting point below 650°C.
6. Process according to claim 5, wherein an aqueous and/or alcohol solution of LiCl, NaF, NaCl and Na4Fe (CN)6 is used.
7. Process according to claim 1, wherein the salt mixture in one of the forms of a solution and a finely-dispersed slurry is applied to the inner wall of the fired mold by pouring it in and out of the mold and then drying it.
8. Process according to claim 7, wherein said solution and slurry of the salt mixture contains a dispersing agent.
9. The process of claim 8, wherein said dispersing agent is methyl cellulose.
10. Process according to claim 4, wherein to said salt mixture solution and/or slurry is added an auxiliary agent that improves wetting of the inner wall of the ceramic mold.
11. Process according to claim 10, wherein said auxiliary agent is a surfactant.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19853512118 DE3512118A1 (en) | 1985-04-03 | 1985-04-03 | METHOD FOR GENERATING AN IMPROVED FINE-NARROWNESS OF THE PRIMARY FABRIC AND / OR THE EUTEKTIKUM OF CASTING PARTS |
| DEP3512118.1-24 | 1985-04-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1288210C true CA1288210C (en) | 1991-09-03 |
Family
ID=6267164
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000505669A Expired - Lifetime CA1288210C (en) | 1985-04-03 | 1986-04-02 | Process for casting aluminum alloys |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0198290B1 (en) |
| JP (1) | JPS61293653A (en) |
| BR (1) | BR8601478A (en) |
| CA (1) | CA1288210C (en) |
| DE (2) | DE3512118A1 (en) |
| ES (1) | ES8703097A1 (en) |
| IL (1) | IL78279A0 (en) |
| SU (1) | SU1760973A3 (en) |
| ZA (1) | ZA862393B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3703416A1 (en) * | 1987-02-05 | 1988-08-18 | Thyssen Guss Ag | Investment casting shell mold for aluminum or WHOSE ALLOYS |
| DE3821204A1 (en) * | 1988-06-23 | 1989-12-28 | Winkelstroeter Dentaurum | Inoculant mixture for coating casting moulds for the production of dental cast skeletons |
| DE4308614A1 (en) * | 1993-03-18 | 1994-09-22 | Fritz Winter Eisengieserei Ohg | Method for producing workpieces made of cast iron, and hollow castings produced accordingly |
| GB9618216D0 (en) * | 1996-08-30 | 1996-10-09 | Triplex Lloyd Plc | Method of making fine grained castings |
| FR2935275B1 (en) * | 2008-08-29 | 2011-11-04 | Peugeot Citroen Automobiles Sa | LOST MODEL MOLDING PROCESS, LOST MODEL FOR THIS PROCESS |
| KR102545134B1 (en) * | 2015-12-18 | 2023-06-19 | 에이에스케이 케미칼스 엘엘씨 | Molding materials for non-ferrous castings |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE963642C (en) * | 1944-09-30 | 1957-05-09 | Siemens Ag | Process for influencing the surface of cast bodies |
| US3259948A (en) * | 1962-04-09 | 1966-07-12 | Howe Sound Co | Making fine grained castings |
| DE1433969B2 (en) * | 1963-11-19 | 1973-02-08 | Larsson, Rune, Sandviken (Schweden) | FLUORINE PROTECTIVE LAYER FOR CASTING FORMS AND THE PROCESS FOR THEIR PRODUCTION |
| US3157926A (en) * | 1964-02-14 | 1964-11-24 | Howe Sound Co | Making fine grained castings |
| DE1265356B (en) * | 1965-02-26 | 1968-04-04 | Henry H Harris | Mold |
| NL126286C (en) * | 1965-07-29 |
-
1985
- 1985-04-03 DE DE19853512118 patent/DE3512118A1/en not_active Ceased
-
1986
- 1986-03-26 IL IL78279A patent/IL78279A0/en not_active IP Right Cessation
- 1986-03-27 EP EP86104247A patent/EP0198290B1/en not_active Expired - Lifetime
- 1986-03-27 DE DE8686104247T patent/DE3671607D1/en not_active Expired - Fee Related
- 1986-04-01 ZA ZA862393A patent/ZA862393B/en unknown
- 1986-04-02 CA CA000505669A patent/CA1288210C/en not_active Expired - Lifetime
- 1986-04-02 BR BR8601478A patent/BR8601478A/en not_active IP Right Cessation
- 1986-04-02 JP JP61074397A patent/JPS61293653A/en active Pending
- 1986-04-02 SU SU864027428A patent/SU1760973A3/en active
- 1986-04-03 ES ES553681A patent/ES8703097A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0198290A2 (en) | 1986-10-22 |
| DE3512118A1 (en) | 1986-10-16 |
| ZA862393B (en) | 1986-11-26 |
| ES8703097A1 (en) | 1987-02-16 |
| EP0198290B1 (en) | 1990-05-30 |
| IL78279A0 (en) | 1986-07-31 |
| JPS61293653A (en) | 1986-12-24 |
| EP0198290A3 (en) | 1987-06-24 |
| SU1760973A3 (en) | 1992-09-07 |
| ES553681A0 (en) | 1987-02-16 |
| BR8601478A (en) | 1986-12-09 |
| DE3671607D1 (en) | 1990-07-05 |
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| Date | Code | Title | Description |
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| MKLA | Lapsed |