Patent Grant
8012275
The present invention relates to a technique for manufacturing a composite-metal-forming material obtained by kneading an additive material with a metallic material, and a technique for manufacturing a composite-metal-formed article.
A metal material with a low melting point is cooled to a temperature at which a solid and liquid are both present, and in this state a carbon nanomaterial is kneaded with the low-melting metal material, to yield a composite material. A method for using a metal forming machine provided with heating means to inject and fill a die with the composite material and obtain a composite metal product is known, as disclosed in Japanese Patent Application Laid-Open Publication No. 2004-136363 (JP 2004-136363 A).
According to the composite forming method disclosed in JP 2004-136363 A, a molten low-melting metal material is cooled to a semi-molten state having a thixotropic property in which a liquid phase and a solid phase are both present. The low-melting metal material is kneaded in this state with a carbon nanomaterial, and a composite material is obtained. A metal forming machine provided with heating means is used to inject the composite material into a die while the thixotropic property is maintained; and a composite metal product is formed using the die.
Specifically, the method stated above is characterized in that the carbon nanomaterial is kneaded with the low-melting metal material in a semi molten state. Since the metal material is in a semi-molten state, the movement of the added carbon nanomaterial is limited, and the carbon nanomaterial can be prevented from rising or settling. As a result, a composite material of good quality can be obtained.
Of the liquid-phase portion and solid-phase portion that constitute the low-melting metal material in a semi-molten state, it is in the solid-phase portion that the carbon nanomaterial cannot be present. Therefore, the carbon nanomaterial composited by the method stated above is present in the liquid-phase portion.
If the added amount of the carbon nanomaterial is increased in order to improve functionality, the viscosity of the liquid-phase portion will increase, and the fluidity of the low-melting metal material in a semi-molten state will accordingly decline. A low-melting metal material in a semi-molten state of such description is harder to inject with a metal forming machine, and is not readily spread to all regions of the cavity of the die.
The technique mentioned above can be used when there is a small amount of carbon nanomaterial to be added, but cannot be used when the added amount is suitable.
An object of the present invention is to provide a composite-metal-forming material that can be used even in a case where the added amount of a carbon nanomaterial is sufficient.
According to a first aspect of the present invention, there is provided method for manufacturing a composite-metal-forming material, comprising: a step for preparing a metal material having a Mg alloy and an Al alloy, and a additive material for being added to the metal material; a step for heating the metal material to a temperature of a region where a solid and a liquid are both present, thereby yielding a semi-molten metal material in a semi-molten state; a step for introducing the additive material to the semi-molten metal material, performing kneading, and obtaining a composite metal material; and a step for heating the composite metal material to a solution temperature of the metal material, and performing a solution treatment, thereby yielding a composite-metal-forming material.
According to the present invention, a solution treatment is additionally performed on the composite metal material manufactured by the step for turning the metal material into a semi-molten state and the step for adding and kneading the additive material. The composite metal material that has been subjected to the semi-solidifying step and the kneading step is composed of a solid phase and a liquid phase. When the solution treatment is performed, the composite metal material assumes a solid solution structure in its entirety.
Since the composite-metal-forming material is in its entirety a solid solution structure, a part of the portion that was the liquid-phase prior to the solution treatment (erstwhile liquid-phase portion) will remain as a new solid-phase portion (new solid-phase portion) when the composite-metal-forming material is heated to a semi-molten temperature at a later step. Specifically, just as some of the erstwhile liquid-phase portion becomes the new solid-phase portion, and some of the erstwhile solid-phase portion becomes the new liquid-phase portion, heating the material after the solution treatment until the semi-molten temperature is reached causes a phase exchange to occur, albeit only partially. The additive material will be entrained in the new solid-phase portion.
However, the amount of the additive material in the new liquid-phase portion will decrease. As a result, the fluidity of the new liquid-phase portion will be improved.
As long as injection forming is performed in a semi-molten state, the additive material will uniformly spread, all regions of the cavity will be filled, and a product of good quality can be obtained.
The additive material is preferably a carbon nanocomposite material. Adding the carbon nanomaterial to the metal material makes it possible to provide a product having exceptional strength and heat conductivity. Since the material is mainly in a semi-molten state, it is possible to provide a formed product in which the carbon nanomaterial is uniformly dispersed, with no risk of the carbon nanomaterial aggregating.
The additive material is preferably a carbon nano-composite material formed by a step for mixing a carbon nanomaterial and a metal powder, and obtaining a carbon nano-composite metal powder; a step for compacting the carbon nano-composite metal powder into a solid, and obtaining a preform; a step for heating the preform in a vacuum, inert gas, or non-oxidizing gas atmosphere to a temperature of a region where a solid and a liquid are both present; and a step for applying pressure to the heated preform.
When the step for mixing the carbon nanomaterial with a metal powder and obtaining the carbon nano-composite metal powder is performed, the carbon nanomaterial deaggregates and is able to cover the metal powder; therefore, re-aggregation of the carbon nanomaterial can be prevented.
A step is subsequently performed whereby the preform formed by compacting the carbon nano-composite metal powder into a solid is heated to the temperature at which a solid and liquid are both present, and pressurized in that state; however, the powder is deaggregated in the mixing step, and the carbon nanomaterial covering is compression-deformed at the temperature where a solid and liquid are both present. It is accordingly possible to obtain a compression-formed article in which, the carbon nanomaterial has been adequately dispersed.
A shear force is applied at the same time that the preform is subjected to pressure in the step in which pressure is applied the preform. Applying the shear force at the same time that pressure is applied to the preform makes it possible to effectively destroy an oxide film that surrounds the powder surface. As long as the oxide film is able to be destroyed, the powder grains become closely attached, and the mechanical strength of the compression-formed preform can be increased.
Preferably, the metal powder comprises one selected from the group consisting of Mg, an Mg alloy, Al and an Al alloy. The Mg, Mg alloy, Al, and Al alloy are light metals, and adding the carbon nanomaterial to these metals and increasing the mechanical strength, makes it possible to provide a lightweight yet strong structural material having exceptional heat conductivity and abrasion resistance.
The carbon nanomaterial is preferably a metal-deposited carbon nanomaterial formed by causing a carbide forming element containing an element that reacts with carbon and forms a compound to adhere to a surface. The carbon nanomaterial has poor wettability, however, the carbide forming element has good wettability. Using a metal-deposited carbon nanomaterial having a carbide-forming element adhering to the surface makes it possible to improve the wettability of the carbon nanomaterial.
The metal-deposited carbon nanomaterial is preferably obtained by mixing the carbon nanomaterial with the carbide-forming metal, placing the resulting mixture into a vacuum furnace, and causing the carbide-forming metal to evaporate at a high, temperature in a vacuum. The carbide-forming metal forms a compound with the carbon, and the compound exhibits a bonding effect; therefore, the carbide-forming metal can be securely bonded to the carbon nanomaterial.
The carbide-forming metal is preferably Ti or Si. Ti and Si are both metals having melting points allowing vapor deposition to be performed in a vacuum, and have satisfactory wettability with regard to molten matrix metals. Si and Ti are both readily available, and Si in particular is inexpensive; therefore, both enable the method of the present invention to be used more widely, and are preferred.
There is preferably further included a step for crushing the composite-metal-forming material following the step for obtaining a composite-metal-forming material, whereby chips are obtained.
The composite-metal-forming material is crushed into chips composed of small aggregated masses, but the crushing also work-hardens the material, and the crystal grains hold internal strain (internal stress). Recrystallization occurs when the chips axe heated to the semi-molten temperature. The crystals that have deformed from the working are broken into fine polygonal grains as a result of the recrystallization, and reappear in a new structure comprising a new liquid-phase portion, a new solid-phase portion, and a new grain boundary. As a result, it is possible to obtain a composite metal material wherein the additive material is more reliably entrained in the new solid-phase portion. Since the aggregated masses are small, the transition to a semi-molten state can be performed in a short period of time.
According to another aspect of the present invention, there is provided a method for manufacturing a composite-metal-formed article comprising: a step for supplying to a metal injection machine a composite-metal-forming material manufactured by a method having a step for preparing a metal material comprising a Mg alloy or an Al alloy, and an additive for being added to the metal material; a step for heating the metal material to a temperature of a region where a solid and a liquid are both present, thereby yielding a semi-molten metal material in a semi-molten state; a step for introducing the additive material to the semi-molten metal material, performing kneading, and obtaining a composite metal material; and a step for heating the composite metal material to a solution temperature of the metal material, and performing a solution treatment, thereby yielding a composite-metal-forming material; and a step for using the metal injection machine to heat [the composite-metal-forming material] to a semi-molten temperature, subsequently supply [the composite-metal-forming material] to a cavity of a die, and obtain a composite-metal-formed article.
Since a material having exceptional fluidity is supplied to the cavity, the material will reach all regions of the cavity, and a composite-metal-formed article of high quality can be obtained.
Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which:
(a) through (f) of
a) through (d) are schematic views showing steps for obtaining a composite-metal-formed article via a chipping step and an injection step using the composite-metal-forming material produced in
(a) through (g) of
a) through (d) show steps for obtaining a compression-formed product using the preform manufactured in
a) through (f) show another embodiment of the steps for manufacturing the composite-metal-forming material according to the present invention;
a) through (e) show steps for surface-treating a carbon nanomaterial;
First, an embodiment of a method for manufacturing a composite-metal-forming material according to the present invention will be described based on
As shown in (a) of
The Mg alloy material 11 is, for example, ASTM AZ91D (equivalent to die-cast Mg alloy JIS H 5303 MDC1D). The composition of the material specified by AZ911) is approximately 9 mass % Al and the remaining portion comprises a small quantity of elements, inevitable impurities, and Mg.
F, which extends parallel to the longitudinal axis, is a temperature line corresponding to AZ91D; and P1, P2, and P3, which are indicated on the temperature line F are the semi-molten temperature, a solution treatment temperature, and a room temperature, respectively.
As shown in (b) of
As shown in (c) of
As shown in (d) of
As shown in (e) of
The ingot 21B and billets 22B shown in (f) of
A chipping step and an injection step that are desirably performed following the steps shown in
a) shows the ingot 21B and billets 22B shown in (f) of
It is desirable to break the ingot 21B into chips 27 by administering a crushing treatment as shown in (b) of
As shown in (c) of
The following are believed to be the reasons behind the formation of a new structure comprising the new solid-phase portion 31, the new liquid-phase portion 32, and the new grain boundary 33 shown in
(1) The composite metal material formed into a uniform solid solution by the solution treatment is crushed. The crushing work-hardens the chips, and internal strain occurs in the crystal grains within the structure.
(2) The crushed composite metal material is heated to the semi-molten temperature. Recrystallization occurs when [the crushed composite metal material] reaches the recrystallization temperature (e.g., around 150° C. for Mg). Recrystallization yields stable, crystal grains free from internal strain; however, the crystals deformed by the working are divided into polygonal fine grains. When the divided crystal is produced, a new structure comprising the new liquid-phase portion, the new solid-phase portion, and the new grain boundary is formed.
(3) The above yields a composite metal material having a new structure wherein the carbon nanomaterial 12 is entrained in the new solid-phase portion 31.
Reasons why crushing of the chips causes a new structure to form, are given above; however, even when a composite metal material that has not been crushed is used, using cold working to cause work hardening and heating the material to the recrystallization temperature or above will likely produce the same actions and effects.
In
The die 34 is opened to yield a composite metal-formed article 36, 36, which is shown in (d) of
The outer surfaces of the chips 27 shown in (b) of
A method for obtaining a solution-treated composite-metal-forming material 24 using steps that are different from those in the example shown in
(a) through (f) of
a): A carbon nanomaterial 12 that has a fiber diameter (average value) of 10 nm to 200 nm is prepared, and a metal powder 38 that has a grain diameter (average value) of 4 mm or less is prepared. The metal powder 38 is preferably Mg, an Mg alloy, Al, or an Al alloy.
b): Premixing is performed. Premixing may be performed by introducing a suitable amount of the carbon nanomaterial 12 and the metal powder 38 into a container and shaking the container.
c): The carbon nanomaterial 12 and the metal powder 38 are thoroughly kneaded using mechanical alloying. Mechanical, alloying is a mechanical mixing method in a broad sense, and refers to a “solid-state alloying method using a high-energy attritor or a ball mill” as stipulated in JIS Z2500, or a “method for using a high-energy mill to mechanically stir, mix, and pulverize a variety of types of starting powders; and use a solid-state reaction to achieve an alloyed state,” which is a mechanical alloying method as stipulated by JIS H7004. These methods are universally known; therefore, a description of the apparatus and principles has been omitted.
d): The preceding processes cause the carbon nanomaterial 11 to deaggregate, and yield a carbon nano-composite metal powder 39 in a form in which the metal powder 38 is covered with innumerable particles of the carbon nanomaterial 12. Specifically, (a) through (c) of
e): A die 42 is positioned on a bottom punch 41, and the die 42 is filled with the carbon nano-composite metal powder 39.
f): A top punch 43 is inserted in the die 42, and the carbon nano-composite metal powder 39 is compacted, into a solid while a temperature of about 150° C. is maintained. A preform 44, which is shown in
Powder compaction can be complicated by the properties of the powder. In this event, the powder is introduced into a metal container and pressurized.
(a) of
b): The preform 44 is placed on a bottom punch 46 of a device whereby the atmosphere, temperature, and pressure are freely controlled; with the preform 44 being surrounded by a heater 47. A non-oxidizing atmosphere such as a vacuum or argon gas is maintained; the semi-molten temperature of the metal powder 38 (
As long as the metal powder is, e.g., an ASTM AZ91D (equivalent to die-cast Mg alloy JISH 5303 MDC1D), the semi-molten temperature is set to 585° C., and the pressure of the top punch 48 is set to 100 to 200 MPa.
The method for compression shown in
c): The preform 44 is placed on a bottom punch 46 of a device whereby the atmosphere, temperature, pressure, and rotation are freely controlled; with the preform 44 being surrounded by a heater 47. A vacuum, argon gas, or other non-oxidizing atmosphere is maintained; the semi-molten temperature of the metal powder 38 (
During compression, the bottom punch 46 and the top punch 48 are rotated in opposite directions with respect to each other at a low speed; i.e., about five rotations per minute. A shear force is applied at the same time that the preform is subjected to pressure, whereby an oxide film that surrounds the powder surface can be effectively destroyed. As long as the oxide film is able to be destroyed, the powder grains become closely attached, and the mechanical strength of the compression-formed preform can be increased.
In (b) and (c) of
a) through (c) as described above corresponds to steps for obtaining a compression-formed product.
d): A compression-formed product 49 in which the carbon nanomaterial has been adequately dispersed is obtained.
(a) through (f) of
As shown in
As shown in
Next, as shown in
As shown in
As shown in
The ingot 21B and billets 22B shown in
The carbon nanomaterial 12 prepared as shown in
(a) through (e) of
a): A carbon nanomaterial 51 is prepared; e.g., in an amount of 10 g. The carbon nanomaterial 51 can be the same as the carbon nanomaterial 12 shown in
b): a silicon powder 52 is prepared for use as a carbide-forming element; e.g., in an amount: of 10 g.
c): The carbon nanomaterial 51 and silicon powder 52 are introduced into a mortar 53, and mixed using a pestle 54 for 15 to 30 min.
d): The resulting mixture 55 is introduced into an alumina container 56, which is covered with an alumina lid 57. A non-sealing lid is used for the lid 57, thereby enabling air to pass in and out of the container 56.
c): a vacuum furnace 60 is prepared, the furnace being provided with a sealed furnace body 61, heating means 62 for heating the interior of the furnace body 61, a stand 63 on which the container 56 is placed, and a vacuum pump 64 for forming a vacuum inside the furnace body 61. The container 56 is placed in the vacuum furnace 60.
The heating and pressurizing conditions used in the vacuum furnace 60 are described with reference to
At a degree of vacuum of 6×103 Pa, the furnace temperature is raised from room temperature to 300° C. over five hours.
At a degree of vacuum of 5.3×10−3 to 2.1×10−2 Pa, the furnace temperature is then raised from 300° C. to 1400° C. over four hours.
Conditions are maintained for ten hours at 1400° C. and a degree of vacuum of 2.1×10−2 Pa.
The melting point of Si is 1427° C.; therefore, a temperature just below the melting point (1350° C. to 1400° C.) is maintained, and the Si is held in a state of saturated vapor pressure at this temperature. At 1350° C. the saturated vapor pressure is about 1.3×10−3 Pa, and at 1400° C. the saturated vapor pressure is about 2.1×10−2 Pa. These approximate degrees of vacuum can be readily attained using a vacuum furnace, and therefore a processing temperature of 1350° C. to 1400° C. is suitable. However, the evaporation rate at 1350° C. is low, and the processing temperature in the present embodiment is 1400° C. so that the evaporation rate will be higher.
SiC (silicon carbide), which is a compound of Si and carbon, will be described below. The standard free energy of formation of SiC is −39.6 kJ/mol at 1400° C., and since this condition can be met, Si vapor is thought to react with the carbon in the carbon nanomaterial and form SiC.
Therefore, should the mixture be introduced into a semi-sealed container, and the Si powder caused to evaporate, bubble stirring will occur, and Si microparticles can be caused to adhere to the carbon nanomaterial.
The conditions are maintained for long period of time; i.e., 10 hours, in order for stirring and reacting to be adequately performed. It shall be apparent that the lime over which the conditions are maintained may be increased or decreased according to the mixture ratio, the throughput, and other conditions.
Heating is terminated after 19 hours; however, furnace cooling is performed while a degree of vacuum of 1.1×10−3 Pa is maintained. Furnace cooling is a method for cooling the manufactured articles in an extremely gradual manner.
A metal-deposited carbon nanomaterial 65 comprises a deaggregated carbon nanomaterial 51, and multiple Si microparticles 66 uniformly adhering to the surface of the carbon nanomaterial 51. As previously stated, the Si microparticles 66 are obtained by crystallizing Si, which is an element that reacts with carbon and forms a compound.
It is important that the Si microparticles 66 adhere to the carbon nanomaterial 51 with SiC as the carbide interposed therebetween. Since the carbon nanomaterial 51 has poor wettability, a concern is presented that the contact strength would be inadequate if the Si microparticles were used alone. In this regard, causing Si microparticles to adhere to the surface of the carbon nanomaterial 51 enables a SiC reaction layer to form at the interface, and the Si microparticles 66 can be caused to securely adhere to the carbon nanomaterial 51.
Replacing the carbon nanomaterial 12 shown in
The metal material may be an Al alloy as well as an Mg alloy. If an Al alloy is used, an Al—Si system alloy is preferred.
Even if the Si used as a carbide-forming metal (an element that reacts with metallic carbon and generates a compound) is substituted for Ti, the same effect in terms of an improvement in mechanical strength can be obtained, although a detailed description thereof is omitted. Furthermore, in addition to Si and Ti, Zr (zirconium) and V (vanadium) can be employed for use in forming carbide. However, Si and Ti are both readily available, and Si in particular is inexpensive; therefore, both enable the method of the present invention to be used more widely, and are preferred.
Other than Mg or an alloy thereof having a melting point of about 650° C., the metal powder (matrix metal material) may be Al or an alloy thereof having a melting point of about 660° C., Sn or an alloy thereof having a melting point of about 232° C., and Pb or an alloy thereof having a melting point of about 327° C. Any type of metal powder may be used as long as it is a low-melting metal or alloy having a melting point that does not exceed 700° C.
In particular, Mg, Al and alloys of both are light metals. Adding the carbon nanomaterial to these metals and increasing the mechanical strength makes it possible to provide a lightweight yet strong structural material having exceptional heat transmission properties and abrasion resistance.
The present invention is preferred for a method for manufacturing a composite-metal-formed article obtained by combining a carbon nanomaterial with a metal material.
Obviously, various minor changes and modifications of the present invention are possible in light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
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| Number | Date | Country |
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| 1016477 | Jul 2000 | EP |
| Number | Date | Country | |
|---|---|---|---|
| 20100064851 A1 | Mar 2010 | US |
