U.S. patent application number 11/547257 was filed with the patent office on 2011-06-09 for aluminum alloy casting material for heat treatment excelling in heat conduction and process for producing the same.
This patent application is currently assigned to NIPPON LIGHT METAL COMPANY, LTD.. Invention is credited to Hiroshi Horikawa, Hidetoshi Kawada, Sanji Kitaoka, Masahiko Shioda, Toshihiro Suzuki, Takahiko Watai.
Application Number | 20110132504 11/547257 |
Document ID | / |
Family ID | 35125098 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110132504 |
Kind Code |
A1 |
Horikawa; Hiroshi ; et
al. |
June 9, 2011 |
Aluminum Alloy Casting Material for Heat Treatment Excelling in
Heat Conduction and Process for Producing the Same
Abstract
An aluminum alloy casting material for heat conduction obtained
by adding Si to an aluminum alloy casting material with enhanced
castability thereby realize enhancement of thermal conductivity.
There is provided an aluminum alloy casting material excelling in
heat conduction. characterized in that it comprises 5 to 10.0 mass
% of Si, 0.1 to 0.5 mass % of Mg and the balance of Al and
unavoidable impurities, the aluminum alloy casting material having
undergone an aging treatment. Further, there is provided a cast
aluminum alloy casting material that while having castability and
mechanical strength equivalent to or higher than those of
conventional cast aluminum alloys, is also enhanced in heat
conduction; and provided a process for producing the cast aluminum
alloy. In particular, there are provided a cast aluminum alloy and
process for producing the same, wherein Si is contained in an
amount of 6.0 to 8.0 mass %, the elements other than Si and Al each
in simple form in an amount of .ltoreq.0.6%, and wherein the amount
of Si solid-dissolved in aluminum parent phase is regulated to
0.5-1.1 mass % while the area ratio of crystallizate in metal
structure is regulated to 5-8%. In this connection, the amount of
Si solid-dissolved and the area ratio of crystallizate can be
attained by performing of heating retaining treatment of the
subject matter of cast aluminum alloy after casting operation at
400.degree. to 510.degree.C. for .gtoreq.1 hr.
Inventors: |
Horikawa; Hiroshi;
(Shizuoka, JP) ; Kitaoka; Sanji; (Tokyo, JP)
; Shioda; Masahiko; (Tokyo, JP) ; Suzuki;
Toshihiro; (Shizuoka, JP) ; Watai; Takahiko;
(Shizuoka, JP) ; Kawada; Hidetoshi; (Shizuoka,
JP) |
Assignee: |
NIPPON LIGHT METAL COMPANY,
LTD.
Tokyo
JP
|
Family ID: |
35125098 |
Appl. No.: |
11/547257 |
Filed: |
April 5, 2005 |
PCT Filed: |
April 5, 2005 |
PCT NO: |
PCT/JP05/06639 |
371 Date: |
September 28, 2007 |
Current U.S.
Class: |
148/698 ;
148/415; 420/546; 420/548 |
Current CPC
Class: |
C22C 21/02 20130101;
C22F 1/043 20130101 |
Class at
Publication: |
148/698 ;
148/415; 420/548; 420/546 |
International
Class: |
C22F 1/043 20060101
C22F001/043; C22C 21/04 20060101 C22C021/04; C22C 21/08 20060101
C22C021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2004 |
JP |
2004-111496 |
Apr 7, 2004 |
JP |
2004-113584 |
Claims
1. An aluminum alloy casting material having excellent thermal
conductivity, comprising 5-10% by mass of silicon, 0.1-0.5% by mass
of magnesium, the remainder comprising aluminum and inevitable
impurities, and upon which an aging treatment has been
performed.
2. The aluminum alloy casting material having excellent thermal
conductivity recited in claim 1, further comprising 0.3-0.6% by
mass of iron.
3. The aluminum alloy casting material having excellent thermal
conductivity recited in claim 1, whereon the aging treatment is
maintained for 1-10 hours at a temperature of 160-270 degrees
Celsius.
4. The aluminum alloy having excellent thermal conductivity recited
in claim 1, wherein, before performing the aging treatment,
solution heat treatment is undertaken by holding for 1-10 hours at
480-540 degrees Celsius, and subsequently quenching by cooling to a
temperature of 100 degrees Celsius or below at a cooling rate of
100 degrees Celsius per second or faster.
5. An aluminum alloy casting having excellent thermal conductivity,
comprising 6.0-8.0% by mass of silicon, the amount of any single
element other than silicon or aluminum being 0.6% by mass or below,
the amount of silicon in solid solution within the aluminum matrix
being adjusted to 0.5-1.1% by mass, and the area ratio of the
crystallized products within the metal structure being adjusted to
5-8%.
6. The aluminum alloy casting recited in claim 5, comprising
6.0-8.0% by mass of silicon, 0.2-0.5% by mass of magnesium, 0.6% by
mass or less of iron, the remainder comprising aluminum and other
elements, the total amount of other elements being 0.2% by mass or
less.
7. The aluminum alloy casting recited in claim 5, wherein the
amount of titanium and/or zirconium is adjusted to 0.03% by mass or
less.
8. The aluminum alloy casting recited in claim 5, having a thermal
conductivity of 160 W/(mk) or more.
9. A method for manufacturing aluminum alloy castings having
excellent thermal conductivity, comprising undertaking a heating
and holding treatment for 1 hour or longer at 400-510 degrees
Celsius on an aluminum alloy casting material of a composition
described in claim 5.
Description
TECHNICAL FIELD
[0001] The present invention concerns an aluminum alloy casting
material having a high thermal conductivity and a manufacturing
methods thereof. The aluminum alloy casting material having a high
thermal conductivity according to the present invention may be used
optimally for heatsinks having a complex shape in order to increase
heat radiation, and heatsinks having a thin-walled portion and the
like.
BACKGROUND ART
[0002] For aluminum alloys in general, the thermal conductivity
increases as the aluminum content of the alloy gets higher.
Therefore, in cases where a high thermal conductivity is necessary,
the use of pure aluminum may be considered, but pure aluminum has
the problems of low strength and low castability, so it was not
possible to cast things having complex shapes and thin-walled
portions.
[0003] Accordingly, in cases where heatsinks having a complex shape
were manufactured, for example, as described in Japanese Unexamined
Patent Publication No. 2001-316748, Japanese Unexamined Patent
Publication No. 2002-3972, and Japanese Unexamined Patent
Publication No. 2002-105571, aluminum alloys with silicon added
were used in order to improve castability, even at the expense of a
certain degree of thermal conductivity.
[0004] However, along with the increase in performance of
electronic devices in recent years, heatsinks with higher
performance have come to be sought. Accordingly, the development of
alloys having better thermal conductivity than conventional
aluminum alloy castings has been awaited.
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0005] In order to solve the problems such as those described above
of the conventional art, the present invention has the objective of
an aluminum alloy casting material for heat treatment wherefor
castability is improved by adding silicon, and at the same time
having improved thermal conductivity.
[0006] Additionally, the present invention has the objective of
providing a method for manufacturing said aluminum alloy casting
material.
Means for Solving the Problems
[0007] The aluminum alloy casting material according to Claim 1
offered by the present invention in order to solve the
abovementioned problems is an aluminum alloy casting material with
excellent thermal conductivity, characterized by containing 5-10.0%
by mass of silicon, 0.1-0.5% by mass of magnesium, the remainder
comprising aluminum and inevitable impurities, whereon aging
treatment has been performed.
[0008] According to Claim 2 of the present application, the
abovementioned aluminum alloy casting material may further contain
0.3-0.6% by mass of iron.
[0009] The aluminum alloy casting materials having such
compositions are, as shall be described herebelow giving
embodiments, aluminum alloy casting materials having excellent
castability in addition to high thermal conductivity and
strength.
[0010] According to Claim 3 of the present application, for the
aging treatment, holding in a temperature of 160-270 degrees
Celsius for 1-10 hours is suggested.
[0011] Additionally, the present invention according to Claim 4
suggests performing solution heat treatment by holding at 480-540
degrees Celsius for 1-10 hours before performing aging treatment,
and subsequently, quenching by cooling to a temperature of 100
degrees Celsius or below at a cooling rate of 100 degrees Celsius
per second or faster.
[0012] As described in the embodiments given, it was discovered
that by performing the aging treatment and solution heat treatment
described above, the thermal conductivity characteristics and
mechanical strength of the abovementioned aluminum alloy casting
materials improve further.
[0013] The inventors of the present invention, as a result of keen
research in order to solve the abovementioned problems, found that
the amount of silicon in solid solution within the matrix of an
aluminum-silicon aluminum alloy casting, and the area ratio of
crystallized products within the metal structure, affect the
thermal conductivity and strength of the casting greatly, and by
optimizing the values of the amount of silicon in solid solution
and the area ratio of the crystallized products in the metal
structure, an aluminum alloy casting with particularly excellent
thermal conductivity, while having sufficient mechanical strength,
is obtainable.
[0014] Additionally, it was discovered that the amount of silicon
in solid solution and the area ratio of the crystallized products
could be controlled by heating and holding treatment after
casting.
[0015] Thus, by the inventions according to Claim 5 of the present
application, an aluminum alloy casting with excellent thermal
conductivity is provided, characterized by containing 6.0-8.0% by
mass of silicon, 0.6% by mass or less of any single elements other
than silicon and aluminum, the amount of silicon in solid solution
within the aluminum matrix being adjusted to 0.5-1.1% by mass,
preferably 0.55-1.05% by mass, more preferably 0.6-1.0% by mass,
and the area ratio of the crystallized products within the metal
structure being adjusted to 5-8%, preferably 5.5-7.5%, more
preferably 6.0-7.0%.
[0016] Here, according to Claim 6 of the present application, the
abovementioned aluminum alloy casting has a composition comprising,
for elements other than silicon and aluminum, 0.2-0.5% by mass of
magnesium, 0.6% by mass or less of iron, and other elements whereof
the total amount is 0.2% by mass or less.
[0017] Additionally, according to Claim 7 of the present
application, for the above-mentioned aluminum alloy casting, in
cases where titanium and/or zirconium is contained within the
abovementioned other elements, it is preferable that the amount of
titanium and/or zirconium is adjusted to 0.03% by mass or less.
[0018] According to Claim 8 of the present application, said
aluminum alloy casting has a thermal conductivity better than that
of conventional aluminum alloy castings, and has a thermal
conductivity of preferably 160 W/(mk) or greater, more preferably
165 W/(mk) or greater.
[0019] Further, the invention according to Claim 9 of the present
application provides a manufacturing method for an aluminum alloy
casting with excellent thermal conductivity, characterized by
containing 6.0-8.0% by mass of silicon, and conducting heating and
holding treatment at 400-510 degrees Celsius for 1 hour or longer
on an aluminum alloy casting material wherein the amount of any
single element other than silicon or aluminum is 0.6% by mass or
below.
[0020] Here the aluminum alloy casting material preferably contains
6.0-8.0% by mass of silicon, 0.2-0.5% by mass of magnesium, 0.6% by
mass or less of iron, the remainder comprising aluminum and other
elements whereof the total amount is 0.2% by mass or less, and the
titanium and/or zirconium within the aluminum alloy casting
material is adjusted to 0.03% by mass or less. The length of time
of the heating and holding treatment of the aluminum alloy casting
material is 1 hour or longer. However, even if the heating and
holding treatment is performed for 7 hours or longer, no further
improvement in the characteristics can be obtained, so it is
preferable to perform the treatment for 7 hours or less.
Effects of the Invention
[0021] It will become possible to optimally manufacture heatsinks
having a complex shape, or heatsinks having a thin-walled portion,
by taking advantage of the characteristics of the aluminum alloy
with excellent castability having excellent thermal conductivity
and mechanical strength described above.
BRIEF EXPLANATION OF THE DRAWINGS
[0022] FIG. 1 A microphotograph showing the structures of as-cast
material and aluminum alloy castings (No. 1, 4-6)
BEST MODES FOR EMBODYING THE INVENTION
[0023] Herebelow, the inventions according to Claims 1 through 4 of
the present application shall be explained.
[0024] It was thought that for aluminum-silicon aluminum alloys,
magnesium has the effect of improving mechanical strength but
lowering thermal conductivity, so that for casting material
requiring a high thermal conductivity, it is preferable to reduce
the magnesium content as much as possible.
[0025] However, the inventors of the present patent application, as
a result of having conducted keen research, discovered that in the
case of the alloy composition of the present application, by adding
magnesium in the range of 0.1-0.5% by mass, if appropriate aging
treatment is performed, the amount of silicon in solid solution
within the matrix is reduced, and the thermal conductivity
improves.
[0026] Accordingly, the invention of the present application makes
the thermal conductivity of an aluminum alloy casting material
higher by adding 0.1-0.5% by mass of magnesium to an
aluminum-silicon aluminum alloy.
[0027] Herebelow, the effects of each component shall briefly be
explained.
(Silicon: 5-10.0% by Mass)
[0028] Silicon has the effect of improving castability. In the case
of casting of things having a complex shape or a thin-walled
portion such as heatsinks, from the viewpoint of castability, it
becomes necessary to add 5% by mass or more of silicon.
Additionally, silicon also has the effects of improving the
mechanical strength, wear resistance, and vibration damping ability
of the casting material. However, as the silicon increases, thermal
conductivity and extensibility are reduced, and if the amount of
silicon exceeds 10% by mass, plastic workability becomes
insufficient, so that it is desirable for the silicon content to be
10.0% by mass or less.
(Iron: 0.3-0.6% by Mass)
[0029] Iron, in addition to improving the mechanical strength of an
aluminum alloy, has the effect of preventing sticking to the die
when casting with the diecast method. This effect becomes marked
when greater than 0.3% by mass of iron is contained. However, as
the amount of iron gets greater, thermal conductivity and
extensibility are reduced, so if the amount of iron exceeds 0.6% by
mass, plastic workability becomes insufficient.
(Magnesium: 0.1-0.5% by Mass)
[0030] During aging treatment, magnesium forms magnesium-silicon
compounds with silicon within the matrix and precipitates, reducing
the amount of silicon in solid solution within the matrix, and
improving thermal conductivity. Further, by the addition of
magnesium, the mechanical strength improves. This effect becomes
marked when the added amount of magnesium is 0.1% by mass or
greater, but when the added amount exceeds 0.5% by mass, the
thermal conductivity gets reduced.
(Inevitable Impurities)
[0031] Since as the amount of impurities increases, the thermal
conductivity is reduced, it is preferable to keep the amount of
inevitable impurities at 0.1% by mass or less. In particular, since
the effect of titanium, manganese, and zirconium on thermal
conductivity is great, it is preferable to suppress this value to
0.05% by mass or less.
(Solution Heat Treatment: 1-10 Hours at 480-540 Degrees Celsius,
and Subsequent Quenching)
[0032] By conducting solution heat treatment under the
abovementioned conditions, segregation at the micro and macro level
that can be seen in the cast structure is alleviated and the
variability of thermal conductivity and mechanical strength are
reduced, the dissolution in solid solution of magnesium-silicon
precipitates within the matrix is facilitated, iron and other
transition elements that are in supersaturated solid solution are
precipitated, and thermal conductivity improves, and further, it is
possible to improve plastic workability by spheroidizing the
silicon particles to improve extensibility.
[0033] If the treatment temperature is less than 480 degrees
Celsius, or if the amount of time the treatment is maintained is
less than 1 hour, the abovementioned effect is insufficient, and on
the other hand, if the treatment temperature exceeds 540 degrees
Celsius, or if the amount of time the treatment is maintained
exceeds 10 hours, localized melting occurs and the possibility of
the strength decreasing becomes greater. In order to obtain more of
the effects of solution heat treatment, it is preferable for the
treatment temperature to be greater than 500 degrees Celsius.
Further, in cases where solution heat treatment is not conducted,
it is preferable for cooling to be done after casting at least
until 200 degrees Celsius is reached, at a rate of 100 degrees
Celsius per second or faster.
(Aging Treatment: 1-10 Hours at 160-270 Degrees Celsius)
[0034] By the abovementioned aging treatment, it is possible to
improve the thermal conductivity of an alloy by precipitating
silicon and magnesium dissolved in solid solution within the matrix
as magnesium-silicon compounds, and reducing the amount of silicon
and magnesium dissolved in solid solution in the matrix.
Additionally, magnesium-silicon compounds improve the mechanical
strength of an alloy. If the aging conditions are below 160 degrees
Celsius or less than 1 hour, since the amount of magnesium-silicon
compounds precipitated is relatively small, the improvement in
thermal conductivity is small. On the other hand, if 270 degrees
Celsius or 10 hours is exceeded, overaging occurs, and strength is
reduced. The conditions for heat treatment may be selected,
similarly with the alloy composition, according to characteristics
such as thermal conductivity and strength, and further, in
consideration of restrictions due to industrial production, but in
consideration of the balance between thermal conductivity and
strength, it is desirable for the aging treatment to be done for
4-8 hours at 180-250 degrees Celsius.
[0035] Herebelow, embodiments of the inventions according to Claims
1 through 4 shall be described.
Embodiment 1
[0036] Alloy casting materials wherein 0, 0.3, 0.5, and 0.6% by
mass of magnesium was added to an aluminum alloy containing 7.0% by
mass of silicon were prepared, and subsequently, the aging
treatments shown in Table 1 were conducted on said casting
materials, and thermal conductivity was measured. The measurement
results for thermal conductivity are shown together in Table 1.
Additionally, for the alloys containing 0 and 0.3% by mass of
magnesium, the amount of silicon and magnesium dissolved in solid
solution was also measured. The results are shown in Table 2.
Casting was done by gravity die casting.
TABLE-US-00001 TABLE 1 Aging Conditions 8 hrs at 8 hours at 4 hours
at 4 hours at No Aging 100 deg C. 180 deg C. 200 deg C. 250 deg C.
0 mass % 170 170 170 172 173 Comp. Ex. 0.1 mass % 165 166 173 177
180 Invention 0.3 mass % 161 163 171 174 176 Examples 0.5 mass %
157 160 169 171 173 0.6 mass % 155 159 162 165 171 Comp. Ex. Units
of thermal conductivity: .lamda./w m.sup.-1 k.sup.-1
TABLE-US-00002 TABLE 2 Amount of Si Amount of Mg Dissolved in
Dissolved in Mg Amount Aging Conditions Solid Solution Solid
Solution Si + Mg 0 mass % No Aging 0.50 mass % <0.01 mass % 0.50
mass % 4 hrs at 200 0.47 mass % <0.01 mass % 0.47 mass % deg C.
0.3 mass % No Aging 0.45 mass % 0.19 mass % 0.64 mass % 4 hrs at
200 0.20 mass % 0.08 mass % 0.28 mass % deg C.
[0037] According to table 1, in the state where no aging treatment
is done, casting material with magnesium added has a lower thermal
conductivity than casting material with no magnesium added, but it
can be seen that if aging treatment is conducted, the thermal
conductivity of casting material with magnesium added has a thermal
conductivity equivalent to or greater than that of a casting
material with no magnesium added. However, for casting material
with 0.6% by mass of magnesium added, the improvement in thermal
conductivity is insufficient, and the thermal conductivity is lower
than that for casting material with no magnesium added. It is
thought that this is because the effect of the reduction in thermal
conductivity due to an increase in the amount of magnesium
dissolved in solid solution is greater than the improvement in
thermal conductivity caused by a reduction in the amount of silicon
dissolved in solid solution.
[0038] Additionally, table 2 shows that if aging treatment is
conducted, the amount of silicon dissolved in solid solution in an
alloy whereto magnesium is added becomes lower.
Embodiment 2
[0039] Casting materials wherein 0 and 0.3% by mass of magnesium
are added to an aluminum alloy containing 7.0% by mass of silicon
and 0.4% by mass of iron were prepared. The casting materials were
cast using the PF die casting method. After conducting solution
heat treatment on the obtained casting material for 2 hours at 500
degrees Celsius, water quenching was done. Subsequently, the
thermal conductivity was measured, and after this, aging treatment
was done for 4 hours at 250 degrees Celsius, and the thermal
conductivity was measured again. The results are shown in table
3.
[0040] According to table 3, in cases also where iron is contained,
in the state wherein aging treatment is not performed on a casting
material with magnesium added, the thermal conductivity is lower
than casting material with no magnesium added, but it can be seen
that if aging treatment is performed, the thermal conductivity
improves to an equivalent level or better than a casting material
with no magnesium added.
TABLE-US-00003 TABLE 3 Aging Conditions Mg Amount No Aging 4 hrs at
250 deg C. 0 mass % 168 170 Comparative Example 0.3 mass % 158 175
Invention Example Units of thermal conductivity: .lamda./w m.sup.-1
k.sup.-1
[0041] The inventions according to Claims 5 through 9 of the
present application shall be explained.
[0042] In preferred embodiments of the present invention, the
aluminum alloy casting with excellent thermal conductivity of the
present invention contains 6.0-8.0% by mass of silicon, 0.6% by
mass or less of any single element other than silicon or aluminum,
the amount of silicon in solid solution within the aluminum matrix
being adjusted to 0.5-1.1% by mass, and the area ratio of the
crystallized products within the metal structure being adjusted to
5-8%.
[0043] Here, the abovementioned aluminum alloy casting preferably
has a composition comprising, for elements other than silicon and
aluminum, 0.2-0.5% by mass of magnesium, 0.6% by mass or less of
iron, and other elements with a total amount of 0.2% by mass or
less.
[0044] Herebelow, the effects of each component and the area ratio
of the crystallized products, and the reason for restriction shall
be explained.
(Silicon: 6.0-8.0% by Mass)
[0045] Silicon has the effect of improving castability. In cases
where things having a complex shape or a thin-walled portion such
as heatsinks are cast, in order to achieve sufficient castability,
it is necessary to make the silicon content 6.0% by mass or more.
This silicon crystallizes as silicon based crystallizations, and
has the effect of improving the mechanical strength, wear
resistance, and vibration damping of the casting. Additionally, the
further the silicon content is increased, castability and the like
improves, but if the silicon content exceeds 8.0% by mass, the
thermal conductivity is reduced. Therefore, for the objective of
the present invention, the silicon content must be within the range
of 6.0-8.0% by mass.
(Magnesium: 0.2-0.5% by Mass)
[0046] Magnesium is not a necessary element for the present
invention. However, magnesium forms magnesium based crystallized
products, and has the effect of improving mechanical strength, so
in cases where mechanical strength is particularly sought, it is
preferable that magnesium be contained. This effect becomes marked
at 0.2% by mass or greater, and when 0.5% by mass is exceeded,
thermal conductivity is reduced. Further, a portion of the
magnesium forms magnesium-silicon precipitates, having the effect
of improving mechanical strength. Therefore, in cases where
magnesium is contained, it is preferable that this is in the range
of 0.2-0.5% by mass.
(Iron: 0.6% by Mass or Less)
[0047] Iron is an impurity that gets mixed in inevitably, but along
with improving mechanical strength, in cases where the die casting
method is used, it has the effect of suppressing sticking to the
die. However, as the amount of iron increases, thermal conductivity
and extensibility are reduced, and if the iron content exceeds 0.6%
by mass, plastic workability becomes insufficient. Accordingly,
even if iron gets mixed in inevitably, it is preferable to keep the
iron content at 0.3% by mass or less.
(Total Amount of Elements Other than Silicon, Aluminum, Magnesium,
and Iron)
[0048] The aluminum alloy casting of the present invention may
contain elements other than silicon, magnesium, iron, and aluminum
if their total amount is 0.2% by mass or less. These elements are
normally inevitable impurities, but it is not necessary for them to
be so considered. Substantially, titanium, manganese, chromium,
boron, zirconium, phosphorus, calcium, sodium, strontium, antimony,
zinc, and the like may be given as these elements.
[0049] Additionally, here, the effect that titanium, manganese, and
zirconium have on the thermal conductivity is great, so that it is
preferable that their amounts be suppressed to 0.05% by mass or
less.
(Amount of Silicon in Solid Solution: 0.5-1.1% by Mass) (Preferable
Range: 0.55-1.05% by Mass, More Preferable Range: 0.6-1.0% by
Mass)
[0050] In the aluminum alloy casting, the amount of silicon in
solid solution has a large effect on the thermal conductivity
thereof, and if the amount of silicon in solid solution exceeds
1.1% by mass, the thermal conductivity is reduced. On the other
hand, if the amount of silicon in solid solution is less than 0.5%
by mass, then a sufficient mechanical strength cannot be
obtained.
(Area Ratio of Crystallized Products: 5-8%) (Preferable Range:
5.5-7.5%, More Preferable Range: 6.0-7.0%)
[0051] The inventors of the present invention have newly discovered
that in aluminum alloy castings, when the area ratio of
crystallized products exceeds 8%, the crystallized products inhibit
thermal conductivity. Additionally, extensibility becomes low. On
the other hand, if the area ratio of crystallized products is low
at less than 5%, sufficient strength cannot be obtained.
[0052] The inventors of the present invention discovered that the
abovementioned aluminum alloy is obtainable by further performing
heating and holding treatment to a predetermined temperature on a
conventional aluminum alloy casting with excellent castability.
[0053] That is, in the manufacturing method according to the
present invention, first, an aluminum alloy casting material having
a predetermined composition is manufactured. For the manufacturing
method, an appropriate conventionally known casting method may be
used, such as the molten metal casting method, the DC method, the
die casting method, and in some cases, commercially available
aluminum alloy castings may be used as a material for the method of
the present invention. The aluminum alloy casting materials to be
used contain 6.0-8.0% by mass of silicon, and 0.6% by mass or less
of any single element other than silicon or aluminum, and more
preferably contains 6.0-8.0% by mass of silicon, 0.2-0.5% by mass
of magnesium, and 0.6% by mass or less of iron, the remainder
comprising aluminum and other elements in a total amount of 0.2% by
mass or less. As examples of this kind of aluminum alloy casting,
castings cast with JIS AC4C and AC4CH alloys may be given.
[0054] Next, heating and holding treatment is done to 400-510
degrees Celsius on the abovementioned aluminum alloy casting
material. By such a heating and holding treatment, silicon that was
in solid solution within the matrix precipitates, and the amount of
silicon in solid solution within the matrix becomes in the range of
0.5-1.1% by mass, and concurrently, a portion of the crystallized
products dissolves in solid solution in the matrix, and the area
ratio of the crystallized products becomes in the range of
5-8%.
[0055] Here, if the heating and holding temperature exceeds 510
degrees Celsius, the amount of crystallized products that dissolve
in solid solution in the matrix becomes great, and as a result, the
area ratio of the crystallized products is reduced, and at the same
time, the amount of silicon in solid solution becomes great, so the
thermal conductivity is reduced. Additionally, the mechanical
strength is also reduced. In contrast, if the heating and holding
temperature is 400 degrees or less, the silicon within the matrix
does not precipitate, and the amount of silicon in solid solution
does not decrease, so the thermal conductivity does not improve.
Additionally, a portion of the crystallized products is not
dissolved in solid solution in the matrix, so that the area ratio
of the crystallized products becomes large, and thermal
conductivity is reduced.
[0056] Additionally, it is preferable for the heating and holding
treatment to be performed for 1 hour or longer. Additionally, even
if heating and holding is done for longer than 5 hours, the amount
of silicon in solid solution and the area ratio of the crystallized
products does not change much further. Therefore, from a cost
standpoint, it is preferable that the holding time be less than 5
hours.
[0057] After heating and holding, cooling is done to room
temperature, but the subsequent cooling can be done by water
cooling, or slow cooling can be done by furnace cooling. The amount
of precipitates differs according to the cooling rate, and the
amount of silicon in solid solution changes, but in the case of the
alloy of the present invention, silicon already precipitates during
heating and holding treatment, and the amount of silicon in solid
solution is small, so its effects are small. In cases where even a
small increase in strength is desired, water cooling is preferable.
However, in the case of water cooling, the cooling rate will differ
for different portions, so deformation can easily occur during
cooling, so that for castings having a thin-walled portion such as
heatsinks, slow cooling is preferable.
[0058] Herebelow, the inventions according to Claims 5 through 9
shall be explained in further detail using embodiments.
Embodiment 3
[0059] An aluminum alloy casting material (corresponding to JIS
AC4C) comprising 7.1% by mass of silicon, 0.32% by mass of
magnesium, 0.2% by mass of iron, and aluminum, the total content of
other elements being 0.2% by mass or below, was cast into
2034.times.2000 mm by the DC casting method. The obtained as-cast
material (No. 1) was maintained at 380 degrees Celsius, 420 degrees
Celsius, 450 degrees Celsius, 500 degrees Celsius, 535 degrees
Celsius, and 550 degrees Celsius for 5 hours, and subsequently
cooled to room temperature by water cooling, and aluminum alloy
castings (No. 2-7) were obtained.
[0060] Observation of the structure by microscope was done for the
as-cast material (No. 1) and the aluminum alloy castings (No. 4-6)
obtained by performing heating and holding treatment in the
abovementioned manner. A portion of the results are shown in FIG.
1.
[0061] Further, regarding each of the abovementioned as-cast
material and the aluminum alloy castings, thermal conductivity,
tensile strength, amount of silicon in solid solution, and the area
ratio of crystallized substances was measured.
[0062] Here, regarding the amount of silicon in solid solution, the
silicon content of the alloy and the amount of silicon within
thermal phenol residue was determined by chemical analysis, and the
amount of silicon in solid solution was taken to be the difference
when the amount of silicon within the phenol residue was subtracted
from the amount of silicon within the obtained alloy. The thermal
phenol dissolution residue was recovered by filtering the product
with a membrane filter (0.1 .mu.m) after dissolving the alloy with
thermal phenol.
[0063] Additionally, regarding the area ratio of the crystallized
products, after the casting was mirror polished, it was set in an
image processing/analysis device, and measured.
[0064] Measurement was done by measuring 10 fields of view where 1
field of view was 0.014 square millimeters, and taking the average
values.
[0065] The results of the above measurements are shown in table
1.
TABLE-US-00004 Heating and Amt. of Si Area Ratio of Holding in
Solid Crystallized Thermal Tensile Temp. Solution Products
Conductivity Strength Elongation No. (deg C.) (mass %) (%) (W/m k)
(MPa) (%) Note 1 As-Cast 0.92 10.0* 159 220 15 Cp. Ex. 2 380 0.48*
9.8* 158 150 17 Cp. Ex. 3 420 0.59 6.9 187 163 21 Inv. Ex. 4 450
0.63 6.2 184 166 25 Inv. Ex. 5 500 0.98 6.8 168 228 24 Inv. Ex. 6
535 1.23* 5.5 158 249 25 Cp. Ex. 7 550 1.26* 5.0 153 225 25 Cp. Ex.
*Outside the range of the present invention
[0066] As can be seen from the results shown in table 1, as-cast
material whereto heating and holding treatment has not been done
(No. 1), and comparative aluminum alloy casting (No. 2) wherefor
the heating and holding temperature was low, have a large area
ratio of crystallized products, and for this reason, thermal
conductivity and elongation are low. This confirms that the
crystallized products are suppressing thermal conductivity.
[0067] Additionally, it can be seen that for comparative aluminum
alloy castings (No. 6-7) wherefor the heating and holding
temperature is high, the amount of silicon in solid solution
increases, and thermal conductivity becomes low.
[0068] In comparison, the aluminum alloy castings according to the
present invention (No. 3-5), all have values for the amount of
silicon in solid solution and the area of crystallized products
that are within the optimal range, and it can be seen that the
thermal conductivity, tensile strength, and elongation are all high
numerical values.
Embodiment 4
[0069] Heating and holding treatment was done on the as-cast
material obtained in embodiment 3 at 450 degrees Celsius for 0.5
hours, 1 hour, 3 hours, and 7 hours respectively, and subsequently
slow-cooled to room temperature to obtain aluminum alloy castings
(No. 8-11). Regarding the obtained aluminum alloy casting, the
amount of silicon in solid solution, the area ratio of the
crystallized products, thermal conductivity, tensile strength, and
elongation were measured in the same manner as embodiment 3.
[0070] The results are shown in table 2.
TABLE-US-00005 TABLE 2 Heating and Amt. of Si Area Ratio Holding in
Solid Crystallized Thermal Tensile Time Solution Products
Conductivity Strength Elongation No. (hr) (mass %) (%) (W/m k)
(MPa) (%) Note 8 0.5 hr* 0.47* 8.9* 156 152 18 Cp. Ex. 9 1.0 hr
0.60 6.7 185 165 21 Inv. Ex. 10 3.0 hr 0.62 6.6 183 164 23 Inv. Ex.
11 7.0 hr 0.63 6.1 184 165 24 Inv. Ex. *Outside the range of the
present invention
[0071] As can be seen from the results in table 2, when the time of
heating and holding treatment is 0.5 hours, the crystallized
products do not sufficiently dissolve in solid solution, and it can
be seen that as a result, thermal conductivity, tensile strength,
and elongation are reduced.
* * * * *