U.S. patent application number 17/646917 was filed with the patent office on 2022-08-11 for method for manufacturing metal foam.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Koji YAMAMOTO.
Application Number | 20220251682 17/646917 |
Document ID | / |
Family ID | 1000006127912 |
Filed Date | 2022-08-11 |
United States Patent
Application |
20220251682 |
Kind Code |
A1 |
YAMAMOTO; Koji |
August 11, 2022 |
METHOD FOR MANUFACTURING METAL FOAM
Abstract
A highly-productive method for manufacturing a metal foam,
capable of easily manufacturing a molded article having a desired
shape is provided. A method for manufacturing a metal foam includes
dissolving hydrogen in a mixture containing a molten metal and a
thickener, and thereby manufacturing a precursor in which an amount
of solid-soluted hydrogen in the metal is saturated, charging the
precursor into a mold, and solidifying the precursor charged into
the mold under a reduced-pressure atmosphere, or solidifying the
precursor charged into the mold and then heating the solidified
precursor under a reduced-pressure atmosphere.
Inventors: |
YAMAMOTO; Koji; (Toyota-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
1000006127912 |
Appl. No.: |
17/646917 |
Filed: |
January 4, 2022 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 1/08 20130101; C22C
21/00 20130101; C22C 2001/086 20130101 |
International
Class: |
C22C 1/08 20060101
C22C001/08; C22C 21/00 20060101 C22C021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 2021 |
JP |
2021-019331 |
Claims
1. A method for manufacturing a metal foam comprising: dissolving
hydrogen in a mixture containing a molten metal and a thickener,
and thereby manufacturing a precursor in which an amount of
solid-soluted hydrogen in the metal is saturated; charging the
precursor into a mold; and solidifying the precursor charged into
the mold under a reduced-pressure atmosphere, or solidifying the
precursor charged into the mold and then heating the solidified
precursor under a reduced-pressure atmosphere.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2021-019331, filed on
Feb. 9, 2021, the disclosure of which is incorporated herein in its
entirety by reference.
BACKGROUND
[0002] The present disclosure relates to a method for manufacturing
a metal foam.
[0003] Metal foams which are porous materials made of a metal or an
alloy and have a number of pores inside thereof are known. Since
metal foams have an excellent impact energy absorption property and
a sound deadening property, and have a light weight, they are used
as multi-functional materials in a variety of fields. However,
because of their high material costs and complicated manufacturing
processes, their manufacturing costs are high, so it has been
desired to reduce these costs.
[0004] International Patent Publication No. WO2010/106883 discloses
a method for manufacturing a precursor of a metal foam and a method
for manufacturing a metal foam, which have the following features.
The manufacturing method disclosed in International Patent
Publication No. WO2010/106883 makes it possible to easily
manufacture a precursor of a metal form and/or a metal foam without
using an expensive foaming agent powder. This manufacturing method
improves the sphericity of pores in the metal foam and increases
the porosity of the metal foam by adding alumina when friction stir
processing (FSP) is performed. Firstly, a die-cast molded article
containing a gas inside thereof is manufactured by a die-casting
method. Next, a precursor of a metal foam is manufactured by
uniformly dispersing the gas and pore-forming nuclei contained
inside the die-cast molded article throughout the die-cast molded
article by the FSP. Further, a metal foam is manufactured by
heat-treating the precursor thereof in which the precursor is
heated to a temperature close to its melting point, and thereby
foaming the precursor.
SUMMARY
[0005] However, the manufacturing process of the manufacturing
method disclosed in International Patent Publication No.
WO2010/106883 is complicated. Further, it requires a die-casting
apparatus or the like, so that the manufacturing equipment becomes
larger, thus increasing the manufacturing cost. Therefore, the
manufacturing method disclosed in International Patent Publication
No. WO2010/106883 has a problem that the productivity is low.
[0006] The present disclosure has been made to solve the
above-described problem, and an object thereof is to provide a
highly-productive method for manufacturing a metal foam, capable of
easily manufacturing a molded article having a desired shape.
[0007] A first exemplary aspect is a method for manufacturing a
metal foam including: dissolving hydrogen in a mixture containing a
molten metal and a thickener, and thereby manufacturing a precursor
in which an amount of solid-soluted hydrogen in the metal is
saturated; charging the precursor into a mold; and solidifying the
precursor charged into the mold under a reduced-pressure
atmosphere, or solidifying the precursor charged into the mold and
then heating the solidified precursor under a reduced-pressure
atmosphere.
[0008] According to the present disclosure, it is possible to
provide a highly-productive method for manufacturing a metal foam,
capable of easily manufacturing a molded article having a desired
shape.
[0009] The above and other objects, features and advantages of the
present disclosure will become more fully understood from the
detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not to be considered as limiting the present disclosure.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 shows a flowchart showing a method for manufacturing
a metal foam according to a first embodiment;
[0011] FIG. 2 is a schematic diagram showing a precursor
manufacturing process and a precursor charging process in the
method for manufacturing a metal foam according to first
embodiment;
[0012] FIG. 3 is a schematic diagram showing an example of a
solidifying process in the method for manufacturing a metal foam
according to first embodiment; and
[0013] FIG. 4 is a schematic diagram showing another example of the
solidifying process in the method for manufacturing a metal foam
according to first embodiment.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0014] An embodiment according to the present disclosure will be
described hereinafter with reference to the drawings. However, the
present disclosure is not limited to the below-shown embodiment.
Further, for clarifying the explanation, the following description
and the drawings are simplified as appropriate.
[0015] An overview of a method for manufacturing a metal foam
according to a first embodiment will be described with reference to
FIG. 1. FIG. 1 is a flowchart showing a method for manufacturing a
metal foam according to the first embodiment. As shown in FIG. 1,
the method for manufacturing a metal foam according to this
embodiment includes steps S1 to S3 described below.
[0016] In a precursor manufacturing process in the step S1,
hydrogen is dissolved in a mixture M2 containing a molten metal M1
and a thickener T, and by doing so, a precursor M3 in which the
amount of solid-soluted hydrogen in the metal is saturated is
manufactured. In a charging process in the step S2, the precursor
M3 is charged (e.g., injected or poured) into a mold 1. In a
solidifying process in the step S3, the precursor M3, which has
been charged into the mold 1, is solidified under a
reduced-pressure atmosphere.
[0017] Each of the above-described processes will be described in
detail with reference to FIGS. 2 and 3. FIG. 2 is a schematic
diagram showing the precursor manufacturing process and the
precursor charging process in the method for manufacturing a metal
foam according to the first embodiment. FIG. 3 is a schematic
diagram showing an example of the solidifying process in the method
for manufacturing a metal foam according to the first
embodiment.
[0018] As shown by a stage S1-1 in FIG. 2, in the precursor
manufacturing process in the step S1, firstly, a metal, which is
used as a raw material for a metal foam, and a thickener T are
prepared. As the metal used as the raw material for a metal foam, a
single metal element or an alloy can be used. Examples of such
metals and alloys include aluminum, magnesium, titanium, iron,
zinc, copper, aluminum alloys, magnesium alloys, titanium alloys,
steel materials, zinc alloys, and copper alloys.
[0019] The metal used as the raw material (hereinafter also
referred to as the raw-material metal) is melted in a stirring
container 10. Alternatively, a metal that has been melted in
advance is charged into the stirring container 10. There is no
particular limitation on the form (e.g., the phase or the like) of
the raw-material metal, so a bulk material that can be obtained at
a low cost can be used as the raw material.
[0020] When the molten metal M1 is formed, the raw-material metal
is heated so that its temperature falls within an appropriate
temperature range equal to or higher than the melting point
according to the element or the composition of the metal. For
example, in the case where the raw-material metal is aluminum or an
alloy containing aluminum as its main component, the temperature
should be within a range of 550 to 800.degree. C., preferably
within a range of 650 to 700.degree. C. In the case where the metal
is magnesium or an alloy containing magnesium as its main
component, the temperature should be in a range of 550 to
800.degree. C. In the case where the metal is zinc or an alloy
containing zinc as its main component, the temperature should be
within a range of 300 to 550.degree. C. In the case where the metal
is copper or an alloy containing copper as its the main component,
the temperature should be within a range of 900 to 1,200.degree.
C.
[0021] As for the thickener T, for example, one or a plurality of
types of powders selected from metal powders such as a calcium
powder and a magnesium powder, metal oxide powders such as an
alumina powder and a magnesia powder, ceramic powders such as a
silicon carbide powder and a silicon dioxide powder can be used.
The thickener T increases the viscosity of the molten metal M1, and
is preferably one that is chemically stable in the molten metal
M1.
[0022] By thickening the molten metal M1 within an appropriate
range by using the thickener T, the coarsening of pores during the
foaming process can be suppressed. Further, the thickened molten
metal M1 prevents the gas forming the pores from being released to
the outside of the molten metal M1, and retains the gas in the
molten metal M1 and thereby keeps closed pores. That is, by
adjusting the viscosity of the molten metal M1, it is possible to
control the form (the sphericity, the size, etc.) of the pores
formed inside the molten metal M1, so that the pores are
stabilized.
[0023] The thickener T is added in the molten metal M1 contained in
the stirring container 10, and the molten metal M1 is sufficiently
stirred under the atmosphere by using, for example, a stirring
blade. As a result, a mixture M2 in which the thickener T is
uniformly dispersed in the molten metal M1 is obtained. Regarding
the procedure for obtaining the mixture M2, the heating and the
stirring may be performed after the raw-material metal and the
thickener T are mixed. If necessary, the thickener T may be
uniformly dispersed even further in the molten metal M1 by applying
ultrasonic waves to the mixture M2.
[0024] Next, as shown by a stage S1-2 in FIG. 2, hydrogen is
dissolved in the metal. Examples of the method for dissolving
hydrogen in the metal include a method in which the tip of a
feeding tube 20 is inserted into the mixture M2, which has been
obtained as described above, and a water vapor V, which serves as a
hydrogen source, is blown into the mixture M2 through the feeding
tube 20. Another conceivable method is a method in which the
mixture M2 is left undisturbed under the condition of a high
water-vapor partial pressure (under a high humidity).
Alternatively, a hydrogen gas may be blown into the mixture M2
through the feeding tube 20.
[0025] The method for dissolving hydrogen in the metal is not
limited to the above-described methods as long as the concentration
of hydrogen in the molten metal M1 can be increased. The water
vapor V is added in such an amount that the amount of hydrogen
solid-soluted in the metal is supersaturated. If the amount of
hydrogen solid-soluted in the metal is insufficient, the pores will
not sufficiently grow during the foaming process.
[0026] Next, as shown by a stage S2 in FIG. 2, in the precursor
charging process in the step S2, the above-described precursor M3
is charged (e.g., injected or poured) into a mold 1 whose shape
conforms to that of the article to be produced. It is sufficient if
the mold 1 has a required heat resistance and required durability
according to the heating condition and the pressure-reducing
condition in the solidifying process in the step S3. As for the
material of the mold 1, stainless steel having an excellent heat
resistance and excellent durability, heat-resistant steel having
such properties, or the like can be used. Further, the mold 1 may
also be used as the stirring container 10 as long as the material
can be sufficiently stirred and the required amount of hydrogen can
be solid-soluted into the mixture M2. In this case, there is no
need to transfer (e.g., pour or charge) the molten metal from one
container to another between the processes, so it is more
efficient. The amount of the precursor M3 charged into the mold 1
is adjusted based on the degree of the foaming.
[0027] Next, as shown in FIG. 3, in the solidifying process in the
step S3, the precursor M3 charged into the mold 1 is solidified
under a reduced-pressure atmosphere. To achieve a reduced-pressure
atmosphere, for example, a vacuum apparatus 30a including a vacuum
chamber 31, a vacuum pump 32, and a vacuum valve 33 is used. The
precursor M3 charged into the mold 1 is placed inside the vacuum
chamber 31, and the pressure in the vacuum chamber 31 is reduced by
operating the vacuum pump 32. Note that the pressure-reducing is
preferably started at a temperature at which the metal becomes a
solid solution state. The level of vacuum inside the vacuum chamber
31 is maintained, for example, in an intermediate vacuum state
(i.e., at a pressure of 10.sup.2 Pa to 10.sup.-1 Pa). In the case
where the inside (i.e., the internal space) of the mold 1 can be
brought into a reduced-pressure state by making the inside of the
mold 1 a closed space, the vacuum pump 32 may be connected to the
mold 1.
[0028] During this solidifying process, the hydrogen, which has
been solid-soluted in the metal, is released as the temperature of
the molten metal M1 decreases. The hydrogen is released as a gas.
Further, the released gas expands as the pressure decreases, so
that a larger number of pores are generated inside the molten metal
M1. Regarding the release of hydrogen as a gas, in the case where
alumina, magnesia, or the like is added in the mixture, the gas is
more likely to be released because such an inclusion (i.e., an
additive) acts as pore-forming nuclei. Then, the gas in the molten
metal M1 transforms into bubbles due to the pressure difference
caused by the reduction in pressure inside the vacuum chamber 31,
so that the molten metal M1 solidifies with pores entrapped inside
thereof. In this way, a metal foam including a large number of
pores inside thereof can be manufactured.
[0029] As for the solidifying process in the step S3, instead of
using the above-described method, a method in which the precursor
M3 charged into the mold 1 is first solidified and then heated
under a reduced-pressure atmosphere can also be used. Therefore,
another example of the solidifying process will be explained with
reference to FIG. 4. FIG. 4 is a schematic diagram showing another
example of the solidifying process in the method for manufacturing
a metal foam according to the first embodiment.
[0030] In the other aspect of the solidifying process (Step S3),
firstly, a solidified metal body M4 is formed by quenching and
solidifying the precursor M3 obtained by the processes in the steps
S1 and S2 as shown in a stage S4-1 in FIG. 4. The method for
solidifying the precursor M3 is, for example, a method in which the
precursor M3, together with the mold 1 containing it, is submerged
in a water tank 40 containing a refrigerant R. As a result, a
solidified metal body M4, which is formed by quenching and
solidifying the precursor M3, is obtained. As for the refrigerant
R, water, liquid nitrogen, or the like can be used. However, the
method for solidifying the precursor M3 is not limited to the
above-described method.
[0031] Next, as shown in a stage S4-2 in FIG. 4, a vacuum heating
process is performed on the obtained solidified metal body M4. The
vacuum heating process is performed, for example, by using a vacuum
heating apparatus 30b including a vacuum chamber 31, a vacuum pump
32, a vacuum valve 33, heating means 34 such as a heater, and
cooling means using a nitrogen gas (not shown). The obtained
solidified metal body M4 is placed inside the vacuum chamber 31,
and the inside (i.e., the internal space) of the vacuum chamber 31
is heated by using the heating means 34. Note that the obtained
solidified metal body M4 is heated to a temperature at which the
metal contained in the solidified metal body M4 becomes a solid
solution state. As a result, hydrogen contained in the solidified
metal body M4 is released as a gas.
[0032] Further, after stopping the heating, the pressure inside the
vacuum chamber 31 is reduced by operating the vacuum pump 32, and
the inside of the vacuum chamber 31 is cooled by using the cooling
means at the same time. A metal foam is obtained by cooling and
solidifying the heated solidified metal body M4 under a
reduced-pressure atmosphere. Under the reduced-pressure atmosphere
and in the cooled state, the released gas is fixed in an expanded
state. In this way, it is possible to manufacture a metal foam
including a large number of pores inside thereof.
[0033] As described above, according to the method in which the
precursor M3 is first solidified and then a vacuum heating process
is performed thereon, the temperature of the object to be processed
(i.e., the solidified metal body M4) placed inside the vacuum
chamber 31 can be easily controlled, so that the productivity is
improved. Further, since the accuracy of the control of the
temperature is improved, the quality of the metal foam is
improved.
[0034] Next, the present disclosure will be described in a more
detailed manner based on Examples 1 and 2. However, the present
disclosure is not limited to these examples.
EXAMPLE 1
[0035] In this example, aluminum was used as the raw-material
metal. Molten aluminum was obtained by heating the aluminum to 650
to 700.degree. C. in a stirring container 10. Then, 1.5 wt. % of
granular calcium T1 and 1.5 wt. % of a alumina powder T2 were added
in this molten aluminum, and the molten aluminum was stirred at 500
to 1000 rpm for 20 minutes. As a result, a mixture M2 containing
the molten aluminum, the calcium, and the alumina was obtained.
[0036] Note that the particle diameter of the used alumina powder
T2 was 50 .mu.m. As the alumina powder T2, an oxide that is formed
when a metal that is easily oxidized, such as aluminum, is kept in
a molten state in the atmosphere, and the metal reacts with oxygen
(when the metal is aluminum, it becomes alumina) can be used. When
such an unnecessary oxide (so-called slag) is used as the alumina
powder T2, the manufacturing cost of metal foams can be further
reduced.
[0037] The tip of a feeding tube 20 was placed in the
above-described mixture M2, and a water vapor V was added in (i.e.,
blown into) the mixture M2 through the feeding tube 20. The water
vapor V was added as water (H.sub.2O) in an amount of 3 to 4
mol/kgAl. As a result, a precursor M3 in which the amount of the
solid-soluted hydrogen in the aluminum was saturated was
manufactured. The precursor M3 was manufactured in the
atmosphere.
[0038] The manufactured precursor M3 was transferred from the
stirring container to a mold 1 which was formed so as to have
relatively thin walls. In this embodiment, a mold having a cup-like
shape having an opened top and a closed bottom was used as the mold
1.
[0039] Next, the precursor M3, together with the mold 1 containing
it, was placed inside the vacuum chamber 31 of the vacuum apparatus
30a. Then, the pressure inside the vacuum chamber 31 was reduced
from the atmospheric pressure to about 10 Pa in a state in which
the temperature of the precursor M3 is around 500.degree. C., and
the precursor M3 was cooled and solidified under the
reduced-pressure atmosphere. As a result, hydrogen that had been
solid-soluted in the aluminum was released as a gas.
[0040] Further, the gas was expanded due to the pressure difference
caused by the reduction in pressure, and the molten aluminum was
solidified in a state in which a large number of pores were formed
inside the molten aluminum. Then, the solidified metal foam molded
article was removed from the mold 1, so that porous aluminum having
a density of about 0.9 g/cc and a porosity of about 65% was
obtained.
[0041] Note that the generation of hydrogen by the reaction of the
aluminum and the water vapor V (water) is expressed by the
below-shown Expression (1).
2Al+3H.sub.2O-->AlO.sub.3+6H Expression (1)
EXAMPLE 2
[0042] This example was carried out according to the solidifying
process shown in FIG. 4. Firstly, a precursor M3 was manufactured
in a method similar to that in the Example 1, and charged into a
mold 1. After that, a solidified metal body M4 was obtained by
submerging the precursor M3 charged into the mold 1 in a water tank
40 in which water was contained as a refrigerant R. This solidified
metal body M4 contained at least aluminum, a calcium oxide,
alumina, and hydrogen.
[0043] Next, a vacuum heating process was performed on the obtained
solidified metal body M4 by using a vacuum heating apparatus 30b.
In the vacuum heating process, the solidified metal body M4 charged
into the mold 1 was placed inside the vacuum chamber 31, and the
solidified metal body M4 was heated to around 500.degree. C. After
that, the heating was stopped. Then, the pressure inside the vacuum
chamber 31 was reduced from the atmospheric pressure to about 10
Pa, and the heated solidified metal body M4 was quenched at the
same time. As described above, the vacuum heating process was
performed on the solidified metal body M4, and the cooled and
solidified metal foam molded article was removed from the mold 1,
so that porous aluminum similar to that in the Example 1 was
obtained.
[0044] It should be noted that, for example, a die-casting
apparatus is required in the manufacturing method disclosed in
International Patent Publication No. WO2010/106883 in order to
manufacture a metal foam, so that the manufacturing facility
becomes larger. Further, it is difficult to form a metal foam
having a complicated shape by the method using a die-casting
apparatus. Further, in the manufacturing method disclosed in
International Patent Publication No. WO2010/106883, the process of
obtaining a precursor of a metal foam by repeatedly performing
friction stirring on a die-cast molded article is complicated, so
that its productivity is low.
[0045] In contrast, the method for manufacturing a metal foam
according to this embodiment does not require a die-casting
apparatus and its manufacturing process is simple. Further, as for
the mold 1 used to mold a metal foam, a mold having walls that are
thinner than those of the die-casting mold used in the die-casting
apparatus can be used. Therefore, the cost for the method for
manufacturing a metal foam is low, and therefore its productivity
is high. Further, since it is possible to use a mold having a
complicated shape, a metal foam manufactured by using the method
for manufacturing a metal foam according to this embodiment has
high flexibility in regard to its shape.
[0046] Further, as another method for manufacturing a metal foam,
there is direct foaming in melt method using a hydride such as
titanium hydride and zirconium hydride as a foaming agent. However,
since such a foaming agent is expensive, it increases the
manufacturing cost of metal foams. Further, in the case where a
foaming agent having a low thermal decomposition temperature is
used, the material used as the raw material is limited to those
having relatively low melting points.
[0047] In contrast, in the method for manufacturing a metal foam
according to this embodiment, an inexpensive material such as a
water vapor can be used as the hydrogen source for forming pores.
According to the above-described features, it is possible to
manufacture a metal foam without using an expensive foaming agent,
and thereby to reduce the manufacturing cost of metal foams.
Further, the restrictions on the material of the metal which are
imposed because of the thermal decomposition temperature of the
foaming agent are relaxed.
[0048] Therefore, according to the method for manufacturing a metal
foam according to this embodiment, it is possible to easily
manufacture a molded article having a desired shape by using a
simple apparatus(es) and a simple material(s).
[0049] From the disclosure thus described, it will be obvious that
the embodiments of the disclosure may be varied in many ways. Such
variations are not to be regarded as a departure from the spirit
and scope of the disclosure, and all such modifications as would be
obvious to one skilled in the art are intended for inclusion within
the scope of the following claims.
* * * * *