U.S. patent application number 16/189687 was filed with the patent office on 2019-03-14 for free-machining aluminum alloy extruded material with reduced surface roughness and excellent productivity.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). The applicant listed for this patent is Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Yukimasa Miyata, Takahiro Shikama, Shinji Yoshihara.
Application Number | 20190078180 16/189687 |
Document ID | / |
Family ID | 52586669 |
Filed Date | 2019-03-14 |
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United States Patent
Application |
20190078180 |
Kind Code |
A1 |
Miyata; Yukimasa ; et
al. |
March 14, 2019 |
FREE-MACHINING ALUMINUM ALLOY EXTRUDED MATERIAL WITH REDUCED
SURFACE ROUGHNESS AND EXCELLENT PRODUCTIVITY
Abstract
To obtain an Al--Mg--Si based aluminum alloy extruded material
with a smooth surface and no burning without inhibiting the
productivity. An aluminum alloy billet includes: Si: 2.0 to 6.0% by
mass; Mg: 0.3 to 1.2% by mass; and Ti: 0.01 to 0.2% by mass, a Fe
content being restricted to 0.2% or less by mass, with the balance
being Al and inevitable impurities. The aluminum alloy billet is
subjected to a homogenization treatment by keeping at 500 to
550.degree. C. for 4 to 15 hours. The billet is forcibly cooled to
250.degree. C. or lower at an average cooling rate of 50.degree.
C./hr or higher. Then, the billet is subjected to hot-extruding at
an extrusion rate of 3 to 10 m/min by being heating at 450 to
500.degree. C. The extruded material is forcibly cooled at an
average cooling rate of 50.degree. C./sec or higher and then
subjected to an aging treatment. The extruded material can be
manufactured that has its surface having a ten-point average
roughness Rz of 80 .mu.m or less.
Inventors: |
Miyata; Yukimasa;
(Shimonoseki-shi, JP) ; Yoshihara; Shinji;
(Shimonoseki-shi, JP) ; Shikama; Takahiro;
(Shimonoseki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) |
Kobe-shi |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Kobe-shi
JP
|
Family ID: |
52586669 |
Appl. No.: |
16/189687 |
Filed: |
November 13, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15222608 |
Jul 28, 2016 |
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16189687 |
|
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14915006 |
Feb 26, 2016 |
9657374 |
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PCT/JP2014/072592 |
Aug 28, 2014 |
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15222608 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21C 23/002 20130101;
C22C 21/02 20130101; B21C 29/003 20130101; C22F 1/043 20130101 |
International
Class: |
C22C 21/02 20060101
C22C021/02; B21C 23/00 20060101 B21C023/00; C22F 1/043 20060101
C22F001/043; B21C 29/00 20060101 B21C029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2013 |
JP |
2013-177572 |
Jul 31, 2014 |
JP |
2014-156634 |
Claims
1. An Al--Si--Mg based aluminum alloy extruded material comprising:
Si: 2.0 to 6.0% by mass; Mg: 0.3 to 1.2% by mass; and Ti: 0.01 to
0.2% by mass, a Fe content being restricted to 0.2% or less by
mass, with the balance being Al and inevitable impurities, wherein
the number of AlFeSi particles having a diameter of 5 .mu.m or more
is 20 or less per 50 .mu.m square area of the extruded material,
the number of Mg.sub.2Si particles having a diameter of 2 .mu.m or
more is 20 or less per 50 .mu.m square area of the extruded
material, and a ten-point average roughness Rz of a surface of the
extruded material is 80 .mu.m or less.
2. The Al--Si--Mg based aluminum alloy extruded material according
to claim 1, further comprising one or more kinds of: Mn: 0.1 to
1.0% by mass; and Cu: 0.1 to 0.4% by mass.
3. The Al--Si--Mg based aluminum alloy extruded material according
to claim 1, further comprising one or more kinds of: Cr: 0.03 to
0.1% by mass; and Zr: 0.03 to 0.1% by mass.
4. The Al--Si--Mg based aluminum alloy extruded material according
to claim 2, further comprising one or more kinds of: Cr: 0.03 to
0.1% by mass; and Zr: 0.03 to 0.1% by mass.
5-8. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to an Al--Mg--Si based
aluminum alloy extruded material that is suitable for use in
mechanical parts and the like, requiring many machining processes
during manufacturing procedures and that has high strength and
excellent machinability, and also to a manufacturing method
thereof.
BACKGROUND ART
[0002] Patent Documents 1 to 4 disclose the Al--Mg--Si based
aluminum alloy extruded materials for machining. To improve the
machinability in these aluminum alloy extruded materials for
machining, 1.5% or more by mass of Si is added, and a large amount
of Si crystallized grains (Si phase), which are second-phase hard
particles, are distributed in a matrix.
PRIOR ART DOCUMENT
Patent Document
[0003] Patent Document 1: JP 9-249931 A [0004] Patent Document 2:
JP 10-8175 A [0005] Patent Document 3: JP 2002-47525 A [0006]
Patent Document 4: JP 2003-147468 A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0007] The Al--Mg--Si based aluminum alloy for machining
crystallizes into Si and Mg.sub.2Si during the solidification
process, and also crystallizes into a needle-like
.beta.-AlFeSi-based compound (.beta.-AlFeSi phase) made of Fe as
inevitable impurities, and Al and Si. FIG. 1 shows a micrograph of
a billet before a homogenization treatment. Strip-shaped Si phases
(in gray) are connected in a net shape, in which Mg.sub.2Si phases
(in black) are distributed as dots, while needle-like .beta.-AlFeSi
phases (in white) are formed along the Si phases. Extruding the
Al--Mg--Si based aluminum alloy billet poses a problem in which
burning (pickup) might occur in extruded materials, degrading the
smoothness of the surface of the extruded material.
[0008] The occurrence of burning in the Al--Mg--Si based aluminum
alloy extruded material is based on the following reasons. The
strip-shaped Si phases existing in the billet before extruding
cause a eutectic reaction with an Al phase and a Mg.sub.2Si phase
due to the deformation of material by extruding and the heat
generation during the process resulting from the friction between
the material and a die-bearing portion, thereby causing local
melting. A shearing force upon the extruded material when it passes
through the die-bearing portion makes the material of the surface
of the extruded material (cells surrounded by the Si phases) fall
off starting at the melting point, causing burning of the extruded
material.
[0009] Further, the needle-like .beta.-AlFeSi phases existing in
the billet before extruding cause a eutectic reaction with a
Mg.sub.2Si phase due to heat generation during the extrusion
process, causing local melting. If local melting continuously
occurs to couple melted parts, the material on the surface of the
extruded material will fall off due to the shearing force that the
extruded material receives when passing through the die-bearing
portion, causing burning of the extruded material.
[0010] Although the inner peripheral surface of the die is
mirror-finished, the occurrence of burning might coarsen the
surface of the extruded material, losing the smoothness
thereof.
[0011] The burning generated by the eutectic reaction in the Si,
Al, and Mg.sub.2Si phases can be reduced by applying the
homogenization treatment to the billet before extruding, at a
temperature of 500 to 550.degree. C. for four hours or more, and
separating (spheroidizing) the Si phase crystallized in the strip
shape.
[0012] On the other hand, the burning generated by the peritectic
reaction between the .beta.-AlFeSi and Mg.sub.2Si phases can be
reduced by conducting homogenization treatment at a temperature of
500.degree. C. or higher for a long time (approximately 50 hours
when Si and Fe contents are large), thereby converting the
.beta.-AlFeSi phase into a phase (spherodizing), or by decreasing
the extrusion rate to reduce the amount of heat generated during
processing. However, the long-term homogenization treatment
inhibits productivity and is disadvantageous in terms of cost.
Further, the reduction in the extrusion rate also inhibits
productivity.
[0013] The present invention has been made in view of the foregoing
problems associated with manufacturing of an Al--Mg--Si based
aluminum alloy extruded material for machining, and it is an object
of the present invention to obtain an Al--Mg--Si based aluminum
alloy extruded material with a smooth surface and no burning
without requiring the long-term homogenization treatment and the
reduction in extrusion rate.
Means for Solving the Problems
[0014] An Al--Mg--Si based aluminum alloy extruded material
according to the present invention includes: Si: 2.0 to 6.0% by
mass; Mg: 0.3 to 1.2% by mass; and Ti: 0.01 to 0.2% by mass, a Fe
content being restricted to 0.2% or less by mass, with the balance
being Al and inevitable impurities, wherein the number of AlFeSi
particles having a diameter of 5 .mu.m or more is 20 or less per 50
.mu.m square area of the extruded material, and the number of
Mg.sub.2Si particles having a diameter of 2 .mu.m or more is 20 or
less per 50 .mu.m square area of the extruded material, and wherein
a ten-point average roughness Rz of a surface of the extruded
material is 80 .mu.m or less. The aluminum alloy extruded material
can further contain one or more kinds of: Mn: 0.1 to 1.0% by mass;
and Cu: 0.1 to 0.4% by mass, as needed. The aluminum alloy extruded
material can further contain one or more kinds of: Cr: 0.03 to 0.1%
by mass; and Zr: 0.03 to 0.1% by mass, as needed.
[0015] A method for manufacturing an Al--Mg--Si based aluminum
alloy extruded material according to the present invention includes
the steps of: applying a homogenization treatment to an aluminum
alloy billet having the above-mentioned composition by keeping at
500 to 550.degree. C. for 4 to 15 hours; forcibly cooling the
billet to 250.degree. C. or lower at an average cooling rate of
50.degree. C./hr or higher; hot-extruding the billet at an
extrusion rate of 3 to 10 m/min by heating at 450 to 500.degree.
C.; forcibly cooling the extruded material at an average cooling
rate of 50.degree. C./sec or higher; and applying an aging
treatment to the extruded material. By this manufacturing method,
the above-mentioned Al--Mg--Si based aluminum alloy extruded
material according to the present invention can be obtained.
Effects of the Invention
[0016] Accordingly, the present invention can obtain the Al--Si--Mg
based aluminum alloy extruded material with excellent machinability
and a smooth surface having a ten-point average roughness Rz of 80
.mu.m or less, while reducing burning without being accompanied by
the long-term homogenization treatment as well as reduction in
extrusion rate in the manufacture of the Al--Si--Mg based aluminum
alloy extruded material having a relatively large Si content.
[0017] The Al--Si--Mg based aluminum alloy extruded material in the
present invention has high strength, excellent machinability, and
good appearance due to the smooth surface. Thus, the Al--Si--Mg
based aluminum alloy extruded material enables reduction in amount
of machining processing, and can, in some cases, have a part of its
surface used as a surface of a product as it is (without
machining).
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a scanning electron micrograph of a billet
before a homogenization treatment.
[0019] FIG. 2A shows a scanning electron micrograph of a billet in
Example No. 1 after the homogenization treatment.
[0020] FIG. 2B shows a scanning electron micrograph of an extruded
material obtained from the billet in Example No. 1.
[0021] FIG. 3A shows a scanning electron micrograph of a billet in
Example No. 12 after the homogenization treatment.
[0022] FIG. 3B shows a scanning electron micrograph of an extruded
material obtained from the billet in Example No. 12.
[0023] FIG. 4A shows a scanning electron micrograph of a billet in
Example No. 13 after the homogenization treatment.
[0024] FIG. 4B shows a scanning electron micrograph of an extruded
material obtained from the billet in Example No. 13.
BEST MODE FOR CARRYING OUT THE INVENTION
[0025] An Al--Si--Mg based aluminum alloy extruded material and a
manufacturing method therefor according to the present invention
will be described in more detail below.
(Aluminum Alloy Composition)
[0026] An aluminum alloy in the present invention includes: Si: 2.0
to 6.0% by mass; Mg: 0.3 to 1.2% by mass; and Ti: 0.01 to 0.2% by
mass, with the balance being Al and inevitable impurities. The
aluminum alloy further includes one or more kinds of: Mn: 0.1 to
1.0% by mass; and Cu: 0.1 to 0.4% by mass, as needed. Moreover, the
aluminum alloy includes one or more kinds of: Cr: 0.03 to 0.1% by
mass; and Zr: 0.03 to 0.1% by mass, as needed. Although the
aluminum alloy compositions itself is well known, the present
invention is characterized by that a Fe content in the inevitable
impurities is restricted to 0.2% or less by mass. Each component of
the aluminum alloy in the present invention will be described
below.
Si: 2.0 to 6.0% by Mass
[0027] Silicon (Si) serves to form Si-based crystallized grains (Si
phase) in aluminum, which are second-phase hard particles, and to
improve the fragmentation of chips and the machinability. To this
end, Si needs to be added in an amount of 2% or more by mass that
exceeds the amount of solid solution of Si into aluminum. On the
other hand, the addition of more than 6% by mass of Si might form
coarsened Si phases, whereby the eutectic reaction among the Si
phase, the Al phase, and Mg.sub.2Si phase occur to lower the
melting start point. To prevent the occurrence of local melting and
burning together with a decrease in melting start point, it is
necessary to suppress the amount of heat during an extrusion
process. For this reason, the extrusion rate needs to be reduced.
Therefore, the Si content is set at 2.0 to 6.0% by mass. The lower
limit of Si content is preferably 3.5% by mass, while the upper
limit of Si content is preferably 4.5% by mass.
Mg: 0.3 to 1.2% by Mass
[0028] Magnesium (Mg) precipitates fine particles of Mg.sub.2Si by
the aging precipitation treatment, thereby improving the strength
of the extruded material. Thus, Mg is desirably added in an amount
of 0.3% or more by mass. On the other hand, Mg.sub.2Si is also
formed as crystallized grains during solidification and might cause
peritectic reaction with .beta.-AlFeSi during the extrusion, which
leads to local melting, causing burning of the extruded material.
When the Mg content exceeds 1.2% by mass, the crystallized grains
of Mg.sub.2Si are formed in a large amount, so that the burning of
the extruded material tends to easily occur. Therefore, the Mg
content is set at 0.3 to 1.2% by mass. The lower limit of Mg
content is preferably 0.5% by mass, while the upper limit of Mg
content is preferably 0.9% by mass.
Ti: 0.01 to 0.2% by Mass
[0029] Titanium (Ti) serves to refine a cast structure, thereby
stabilizing the mechanical properties of the extruded material. To
attain this effect, Ti is added. However, when the Ti content is
less than 0.01% by mass, its effect cannot be obtained. On the
other hand, even if the Ti content exceeds 0.2% by mass, the effect
of refining cannot be further improved. Therefore, the Ti content
is set at 0.01 to 0.2% by mass. The lower limit of Ti content is
preferably 0.01% by mass, while the upper limit of Ti content is
preferably 0.1% by mass.
Mn: 0.1 to 1.0% by Mass; and
Cu: 0.1 to 0.4% by Mass
[0030] Manganese (Mn) has an effect of improving the strength of
extruded material by being precipitated as dispersion particles
during the homogenization treatment to thereby refine crystal
grains of the extruded material. For this reason, Mn is added as
needed. When the Mn content is less than 0.1% by mass, the
above-mentioned effect cannot be sufficiently exhibited. On the
other hand, when the Mn content exceeds 1.0% by mass in adding Mn,
the extrudability is degraded. Therefore, the Mn content is set at
0.1 to 1.0% by mass. The lower limit of Mn content is preferably
0.4% by mass, while the upper limit of Mn content is preferably
0.8% by mass.
[0031] Copper (Cu) is added as appropriate, instead of or together
with Mn, to enhance the strength of the extruded material by being
solid-soluted. When the Cu content is less than 0.1% by mass, the
above-mentioned effect cannot be sufficiently exhibited. On the
other hand, when the Cu content exceeds 0.4% by mass in adding Cu,
the corrosion resistance and extrudability of the extruded material
are degraded. Therefore, the Cu content is set at 0.1 to 0.4% by
mass. The lower limit of Cu content is preferably 0.2% by mass,
while the upper limit of Cu content is preferably 0.3% by mass.
Cr: 0.03 to 0.1% by Mass; and
Zr: 0.03 to 0.1% by Mass
[0032] Chrome (Cr) is added as appropriate to suppress
recrystallization and refine crystal grains, thereby enhancing the
strength of the extruded material. However, when the Cr content is
less than 0.03% by mass, the above-mentioned effect cannot be
sufficiently obtained. On the other hand, when the Cr content
exceeds 0.1% by mass in adding Cr, burning tends to occur in the
extruded material during the extrusion process. Therefore, the Cr
content is set at 0.03 to 0.1% by mass.
[0033] Zinc (Zr) is added as appropriate, instead of or together
with Cr, to suppress the recrystallization and refine crystal
particles, thereby enhancing the strength of the extrusion.
However, when the Zr content is less than 0.03% by mass, the
above-mentioned effect cannot be sufficiently obtained. On the
other hand, when the Zr content exceeds 0.1% by mass in adding Zr,
a compound including a mixture of Al and Zr becomes coarsened
during the homogenization treatment, failing to exhibit the effect
of suppressing the recrystallization. Therefore, the Zr content is
set at 0.03 to 0.1% by mass.
Fe: 0.2% or Less by Mass
[0034] Iron (Fe) existing as the inevitable impurity in the
aluminum alloy generates .beta.-AlFeSi phase, which is a
needle-like crystallized grain, during a cooling process after
casting. To reduce the .beta.-AlFeSi content in the billet and to
prevent burning during the extrusion process, the homogenization
treatment needs to be performed to convert the .beta.-AlFeSi phase
into a phase (spherodizing), or the Fe content in the aluminum
alloy needs to be decreased.
[0035] However, to convert the .beta.-AlFeSi phase into a phase,
the homogenization treatment is required to be carried out at a
high temperature for a long time, which degrades the productivity
of the extrusions. In contrast, when the Fe content of the aluminum
alloy is restricted to 0.2% or less by mass, the amount of the
generated .beta.-AlFeSi phases is reduced. A manufacturing method
to be described below can prevent the burning of the extrusions
during the extrusion process without applying the homogenization
treatment for a long time. Note that the Fe content normally
included as the inevitable impurity in the aluminum alloy is
approximately 0.3% by mass.
(Method for Manufacturing Aluminum Alloy Extruded Material)
Homogeneous Treatment Conditions
[0036] The homogenization treatment for the cast billet is
performed under holding conditions of 500 to 550.degree. C. for 4
to 15 hours. A holding temperature is set at 500.degree. C. or
higher, and a holding time is set at 4 hours or more. This is
because strip-shaped crystallized Si phases are divided
(spheroidized) while crystallized Mg.sub.2Si is solid-soluted. As
the holding temperature is higher and the holding time is longer,
these conditions would be more preferable for the homogenization
treatment because they promote the division of Si phase and the
solid solution of Mg.sub.2Si and reduce the burning. However, at a
temperature exceeding 550.degree. C., local dissolution might
occur, while for a holding time exceeding 15 hours, the
productivity of extrusions might be reduced. Therefore, the
homogenization treatment should be performed under holding
conditions, specifically, at a temperature of 500 to 550.degree. C.
and for a time of 4 to 15 hours. Note that these holding conditions
cannot sufficiently achieve the conversion of .beta.-AlFeSi phase
into a phase.
Cooling Conditions after Homogenization Treatment
[0037] After the homogenization treatment, the billet is forcibly
cooled at an average cooling rate of 50.degree. C./hr or higher.
Conventionally, the billet obtained after the homogenization
treatment is taken out of a furnace and cooled by being allowed to
stand, or by being air-cooled. In the real operation, since a
number of high-temperature billets are cooled while being
accumulated, the cooling rate is generally estimated to be less
than 30.degree. C./hr even in air-cooling with fans. No attention
has been paid particularly to the cooling rate after the
homogenization treatment. At an average cooling rate of 50.degree.
C./hr or higher, the billet is forcibly cooled to a temperature of
less than 250.degree. C., which can minimize the precipitation of
Mg.sub.2Si (to such a degree that can prevent the occurrence of
burning during extrusion). At a temperature of 250.degree. C. or
lower, the billet may be allowed to stand to cool to the room
temperature. The desirable average cooling rate is 80.degree. C./hr
or more, which can be achieved by forcibly performing air-cooling
with fans under the condition that the billets are not accumulated.
Further, water cooling is more desirable. In this case, the cooling
rate of about 100,000.degree. C./hr can be achieved.
Extrusion Conditions
[0038] After the homogenization treatment, the billet is reheated
to a temperature of 450 to 500.degree. C. and then subjected to
hot-extruding at an extrusion rate of 3 to 10 m/min. Since the
extruded material in the present invention is a solid-core material
(solid material), the extrusion ratio thereof is relatively small,
and the heat generation therefrom does not become so much during
processing. At an extrusion temperature of less than 450.degree.
C., the temperature of the extruded material at the outlet of an
extrusion machine does not reach 500.degree. C. or higher that is
required for solution. On the other hand, once the extrusion
temperature exceeds 500.degree. C., the processing heat generation
is added, increasing the temperature of extrusion material, leading
to the risk of burning of the extruded material. Therefore, the
extrusion temperature (heating temperature of the billet) is set at
450 to 500.degree. C. At an extrusion rate of less than 3 m/min,
the productivity of extruded materials is degraded. On the other
hand, once the extrusion rate exceeds 10 m/min, the processing heat
generation becomes large, increasing the temperature of material
for extrusion, leading to the risk of burning of the extruded
material. When the extruded material has a corner at its cross
section, the phenomenon of corner cracks tends to occur as metal
does not spread out into the corner. Thus, the extrusion rate is
set at 3 to 10 m/min. In the manufacturing method of the present
invention, the extrusion ratio (i.e. the ratio of the
cross-sectional area of an extrusion container to that of the
extrusion outlet) is preferably in a range of 15 to 40.
Cooling Conditions after Extrusion
[0039] The extruded material obtained directly after the extrusion
process is forcibly cooled (die-quenched) online from the outlet
temperature of the extrusion machine to a temperature of
250.degree. C. or less at an average cooling rate of 50.degree.
C./sec or higher. At a temperature of 250.degree. C. or lower, the
extruded material may be allowed to stand to cool to the room
temperature. By setting the average cooling rate to 50.degree.
C./sec or higher, the precipitation of Mg.sub.2Si is prevented.
Preferable cooling means is water-cooling.
Aging Treatment Conditions
[0040] The extruded material die-quenched is subjected to an aging
treatment. The aging treatment may be performed at a temperature of
160 to 200.degree. C. for 2 to 10 hours.
(Number Density of AlFeSi Particles and Mg.sub.2Si Particles in
Extruded Material)
[0041] The distribution state of the coarse .beta.-AlFeSi particles
and Mg.sub.2Si particles in the Al--Mg--Si based aluminum alloy
extruded material in the present invention reflects the
distribution state of the .beta.-AlFeSi phase and Mg.sub.2Si phase
in the billet after the homogenization treatment (after cooling).
This point will be described referring to scanning electron
micrographs of FIGS. 2A to 4B.
[0042] FIGS. 2A, 3A, and 4A are the scanning electron micrographs
showing the distribution states of .beta.-AlFeSi phases and
Mg.sub.2Si phases in the billets of Examples No. 1, 12, and 13,
respectively. The .beta.-AlFeSi phase is shown as white needle-like
particles, and the Mg.sub.2Si phase is shown as black granular
particles. FIGS. 2B, 3B, and 4B are the scanning electron
micrographs showing the distribution states of AlFeSi particles and
Mg.sub.2Si particles in the extrusion material obtained from these
billets, respectively. The original .beta.-AlFeSi phase is divided
when being extruded and then formed into an aggregate of white
granular particles.
[0043] As shown in Table 2 of Examples to be mentioned later,
referring to FIG. 2B, each of the number of AlFeSi particles having
a diameter of 5 .mu.m or more and the number of Mg.sub.2Si
particles having a diameter of 2 .mu.m or more per certain area (50
.mu.m square) falls within a specified range of the present
invention. Using the distribution state of each kind of particles
shown in FIG. 2B as a reference, as illustrated in FIG. 3B, the
number of AlFeSi particles having a diameter of 5 .mu.m or more is
relatively large, exceeding the specified range of the present
invention, while as illustrated in FIG. 4B, the number of
Mg.sub.2Si particles having a diameter of 2 .mu.m or more is
relatively large, exceeding the specified range of the present
invention. By comparison between the distribution state of
.beta.-AlFeSi phases and that of Mg.sub.2Si phases with reference
to FIGS. 2A, 3A, and 4A, as illustrated in FIG. 2A, the amount of
.beta.-AlFeSi phases is small while the size of Mg.sub.2Si phases
is small; as illustrated in FIG. 3A, the amount of .beta.-AlFeSi
phases is relatively large; and as illustrated in FIG. 4A, the size
of Mg.sub.2Si phases is relatively large.
[0044] In this way, when the number of coarse AlFeSi particles
having a diameter of 5 .mu.m or more in the extruded material is
large, it suggests that the amount of the .beta.-AlFeSi phases in
the billet before the extrusion (after the homogenization
treatment) is large. When the number of coarse Mg.sub.2Si particles
having a diameter of 2 .mu.m or more in the extruded material is
large, it suggests that the size of the Mg.sub.2Si particles in the
billet before the extrusion (after the homogenization treatment) is
large. These relationships can be satisfied except for when the
extrusion ratio is excessively large (e.g., 45 or higher). Thus,
the distribution states of the .beta.-AlFeSi particles having a
diameter of 5 .mu.m or more and of the Mg.sub.2Si particles having
a diameter of 2 .mu.m or more in the extruded material are
specified, thereby indirectly specifying the distribution states of
the .beta.-AlFeSi phases and Mg.sub.2Si phases in the billet before
the extrusion (after the homogenization treatment).
[0045] When the numbers of AlFeSi particles having a diameter of or
more and Mg.sub.2Si particles having a diameter of 2 .mu.m or more
per certain area in the extruded material are within respective
specific ranges in the present invention, the amount of generated
.beta.-AlFeSi phases in the billet is small, the precipitation of
Mg.sub.2Si particles in the billet is suppressed, and the size of
Mg.sub.2Si phase is small. Conversely, when the number of AlFeSi
particles having a diameter of 5 .mu.m or more per certain area in
the extruded material exceeds the specific range in the present
invention, the amount of generated .beta.-AlFeSi phases in the
billet is large. When the number of Mg.sub.2Si particles having a
diameter of 2 .mu.m or more per certain area in the extruded
material exceeds the specific range in the present invention, the
precipitation of Mg.sub.2Si phase in the billet is not sufficiently
suppressed and the size of Mg.sub.2Si phase in the billet is
large.
[0046] The number densities of the AlFeSi particles and Mg.sub.2Si
particles in the present invention will be measured in the
following procedure.
[0047] 1) After grinding the cross section of the extruded material
to have its number density measured, two or more observation
regions in 50 .mu.m square (a pair of sides being in parallel to
the extrusion direction) where the number density is measured are
selected from the cross section by observation with a scanning
electron microscope (SEM).
[0048] 2) The numbers of AlFeSi particles having a diameter of 5
.mu.m or more and of Mg.sub.2Si particles having a diameter of 2
.mu.m or more that are included in these observation regions are
respectively measured (the diameter of each particle being the
circle equivalent diameter). Note that to achieve the accurate
measurements, the magnification scale of SEM is preferably set at
1,000 times or more in measuring the number of particles included
in the region. The particles existing on the side of the
observation region is counted as one.
[0049] 3) The number of each kind of particles is measured for each
selected observation region in the above-mentioned procedure 2),
and an average value of the numbers of each kind of particles in
all selected observation regions is determined.
(Surface Roughness of Extruded Material)
[0050] The billet of the Al--Mg--Si based aluminum alloy with the
above-mentioned composition is subjected to the homogenization
treatment under the conditioned mentioned above, so that the
strip-shaped Si phases crystallized in the billet are spheroidized
and Mg.sub.2Si is solid-saluted. Subsequently, the billet held at
the homogeneous processing temperature is forcibly cooled to
250.degree. C. or lower at a cooling rate of 50.degree. C./hr or
more, which is larger than the usual one, thereby suppressing the
precipitation of Mg.sub.2Si particles during the cooling process.
Since the billet is designed to reduce the amount of generated
.beta.-AlFeSi phases and to suppress the precipitation of
Mg.sub.2Si phases, the peritectic reaction between the
.beta.-AlFeSi phase and Mg.sub.2Si phase is suppressed, and the
precipitation of Mg.sub.2Si phase is suppressed during the
extrusion process, whereby the eutectic reaction among Si, Al, and
Mg.sub.2Si is also suppressed. As a result, an Al--Mg--Si based
aluminum alloy extruded material (extruded material as it is) can
be manufactured that reduces burning of the extruded material and
has a small surface roughness. In the present invention, the
surface roughness of the Al--Mg--Si based aluminum alloy extruded
material can be reduced to 80 .mu.m or lower in terms of ten-point
average roughness Rz (JIS B0601:1994).
EXAMPLES
[0051] An Al--Si--Mg based aluminum alloy having a chemical
composition shown in Table 1 (composition after fusion) was fused
and then subjected to semicontinuous casting, thereby producing a
billet having a diameter of 400 mm. The billet was subjected to the
homogenization treatment under the homogenization treatment
conditions (holding temperature, holding time and cooling rate)
shown in Table 1. Note that the balance of the composition
mentioned in Table 1 included Al and inevitable impurities except
for Fe. Subsequently, extrusion molding was performed on the billet
at an extrusion ratio of 33 under the extrusion conditions shown in
Table 1 (extrusion temperature (billet heating temperature),
extrusion rate and cooling rate), thereby producing a solid
extruded material having a rectangular cross section (100
mm.times.40 mm), followed by an aging treatment at 180.degree. C.
for 4 hours. Note that the term "cooling rate" in each case means a
cooling rate to 250.degree. C.
TABLE-US-00001 TABLE 1 Extrusion condition Homogeneous treatment
conditions Cooling Composition (% by mass) Temperature Cooling rate
Temperature Rate rate No. Si Fe Mg Cu Mn Ti Cr Zr .degree. C. Time
h .degree. C./h .degree. C. m/min .degree. C./s 1 4.02 0.15 0.74
Tr. 0.64 0.02 Tr. Tr. 520 14 80 475 4.5 100 2 5.81 0.16 0.34 Tr.
0.32 0.02 Tr. Tr. 500 14 80 479 5.0 50 3 2.15 0.14 0.46 Tr. 0.95
0.02 Tr. Tr. 520 14 80 480 5.5 80 4 5.64 0.20 0.57 Tr. 0.59 0.03
Tr. Tr. 500 5 50 476 7.5 100 5 5.86 0.15 0.75 0.23 0.41 0.03 Tr.
Tr. 520 5 50 471 8.5 120 6 3.72 0.13 0.74 0.36 Tr. 0.19 Tr. Tr. 520
5 50 470 8.5 200 7 4.53 0.05 0.45 0.38 0.15 0.04 0.03 Tr. 520 5 50
473 5.0 150 8 3.65 0.08 0.35 Tr. Tr. 0.04 Tr. 0.08 520 14 80 490
3.0 130 9 3.54 0.14 0.84 Tr. Tr. 0.06 0.03 Tr. 500 14 50 480 5.0
100 10 6.34* 0.16 0.86 0.25 Tr. 0.02 0.03 Tr. 520 14 120 470 3.0
100 11 1.54* 0.13 0.64 Tr. 0.36 0.02 0.03 Tr. 520 14 120 470 3.0
100 12 5.75 0.22* 0.85 0.23 Tr. 0.02 0.03 Tr. 520 14 120 470 3.0
100 13 4.62 0.16 0.74 Tr. 0.63 0.02 Tr. Tr. 520 14 40* 470 3.0 100
14 4.10 0.14 0.69 Tr. 0.62 0.02 Tr. Tr. 520 3* 80 470 3.0 100 15
3.60 0.17 0.54 Tr. 0.61 0.02 Tr. Tr. 480* 14 120 470 3.0 100 16
3.72 0.26* 0.62 0.21 Tr. 0.02 0.03 Tr. 520 14 120 470 2.5* 100 17
4.46 0.23* 0.70 0.23 Tr. 0.02 0.04 Tr. 520 22* 120 470 3.5 100 18
5.64 0.14 0.90 Tr. 0.58 0.02 Tr. Tr. 520 14 80 520* 3.5 100 19 2.98
0.05 1.02 Tr. 0.57 0.02 Tr. Tr. 520 14 80 470 12.0* 100 20 3.56
0.16 0.65 0.56* Tr. 0.06 Tr. Tr. 500 15 50 480 5.0 90 21 3.67 0.15
0.20* 0.32 Tr. 0.06 Tr. 0.05 520 10 60 475 3.0 120 22 4.32 0.10
1.25* Tr. 0.45 0.05 Tr. Tr. 515 6 100 480 3.0 130 *Item departing
from specific range of the present invention
[0052] The thus-obtained extruded material was used as a sample
material, and each sample material was measured on the number
densities of coarse AlFeSi particles and Mg.sub.2Si particles,
machinability, hardness, surface roughness (ten-point average
roughness Rz), and extrudability in the following way.
(Number Densities of AlFeSi Particles and Mg.sub.2Si Particles)
[0053] After grinding the cross section of each sample material to
have its number density measured, two square observation regions in
50 .mu.m square (a pair of sides being in parallel to the extrusion
direction) for measurement of the number density were selected from
each sample material by observation with a scanning electron
microscope (SEM). For each sample materials, the two selected
observation regions were observed with the SEM having a
magnification scale set at 1,000 times, and then the number of
AlFeSi particles having a diameter (circle equivalent diameter) of
5 .mu.m or more and the number of Mg.sub.2Si particles having a
diameter (circle equivalent diameter) of 2 .mu.m or more that could
be observed in each observation range were measured. The average of
the number of each kind of particles measured in the two
observation regions was determined. The results of the measurements
are shown in Table 2. Note that the particles existing on the side
of the observation region was counted as one.
(Machinability)
[0054] A hole punching was performed on each sample using a
commercially available high-speed steel drill having a diameter of
4 mm under the conditions, specifically, at the number of
revolutions of 1500 rpm and a feeding velocity of 300 mm/min, and
then the number of machining chips in 100 g machining chip
aggregate obtained was counted to measure the machinability of the
extruded material in each sample (fragmentation of machining chip).
Samples containing more than 7000 machining chips are rated
excellent "A"; samples containing 5000 to 7000 machining chips are
rated good "B"; samples containing 3000 to less than 5000 machining
chips are rated satisfactory "C"; and samples containing less than
3000 machining chips are rated unsatisfactory "D". The results of
the measurements are shown in the item "properties" of Table 2.
(Hardness)
[0055] A Rockwall hardness (HRB) of each sample was measured based
on the Rockwell hardness test of JIS Z 2245:2011 as a test
method.
(Surface Roughness)
[0056] The upper, lower, left and right surfaces (four surfaces in
total) of the extruded material in each sample were visually
observed across its entire length. The surface roughness (ten-point
average roughness Rz) of a part of each surface, at which its
surface roughness was determined to be largest by the visually
observation, was measured in the direction vertical to the
extrusion direction based on the standard of JIS B0601:1994. The
maximum ten-point average roughness Rz obtained at each surface is
shown as the surface roughness (ten-point average roughness Rz) of
the extruded material in the item "properties" of Table 2.
(Extrudability)
[0057] The corners of the extruded materials in samples Nos. 1 to
22 were visually observed across the entire length of the extruded
material, and the presence or absence of occurrence of any corner
crack (whether the extrudability were good or bad) was checked for
each sample. Additionally, regarding the billets corresponding to
the extruded materials in specimen Nos. that were observed to have
any corner crack, each billet was extruded at an extrusion rate
lower than the extrusion rate shown in Table 1, and then the
presence or absence of occurrence of the corner crack was checked.
Further, regarding the billets corresponding to the extruded
materials in specimen Nos. observed to have no corner crack, the
billet was extruded at an extrusion rate higher than the extrusion
rate shown in Table 1, and then the presence or absence of
occurrence of the corner crack was checked. At this time, the
extrusion rates were set at any one of 3 m/min, 5 m/min, and 10
m/min, and the homogenization treatment conditions and the
extrusion conditions (except for the extrusion rate) were set as
mentioned in Table 1. Samples that were observed to have no corner
crack at the extrusion rate of 10 m/min were rated as having
excellent extrudability "A"; samples that were observed to have a
corner crack at the extrusion rate of 10 m/min but no corner crack
at the extrusion rate of 5 m/min were rated as having good
extrudability "B"; and samples that were observed to have a corner
crack even at the extrusion rate of 3 m/min were rated as having
bad extrudability "C". The results of the measurements are shown in
Table 2.
TABLE-US-00002 TABLE 2 Number density Properties of particles
Hardness RZ No. AlFeSi Mg.sub.2Si Machinability HRB .mu.m
Extrudability 1 12 12 B 50.6 56 A 2 15 6 A 46.8 64 B 3 14 8 C 50.6
19 A 4 18 12 A 53.0 78 B 5 15 16 A 56.2 70 B 6 10 19 B 54.7 53 A 7
5 14 B 56.4 50 A 8 4 12 B 45.6 50 A 9 11 16 B 38.5 55.8 A 10 19 17
A 60.5 97* B 11 9 15 D 50.5 53.1 A 12 27* 16 B 56.4 85.4* B 13 18
27* B 54.1 90.6* A 14 22* 21* B 53.0 102* A 15 23* 20 B 54.2 105* A
16 21* 16 B 56.1 74.1 A 17 22* 20 B 52.8 72.8 A 18 19 15 B 57.0
132* B 19 4 15 B 59.4 142* A 20 12 11 B 59.4 45.6 C 21 13 4 B 35.2*
56.7 A 22 9 26* B 65.0 87.9* A *Item departing from specific range
of the present invention
[0058] As shown in Tables 1 and 2, the extruded materials Nos. 1 to
9 had the composition specified by the present invention and
satisfied the number densities of the AlFeSi particles and
Mg.sub.2Si particles, whereby these extruded materials had a small
surface roughness (ten-point average surface roughness Rz.ltoreq.80
.mu.m) and excellent machinability. Further, these extruded
materials had a Rockwell hardness of 38 HRB or more and excellent
strength. The extruded materials Nos. 1 to 9 were manufactured by
the manufacturing method specified by the present invention. FIGS.
2A and 2B illustrate the scanning electron micrographs of the
billet No. 1 (after the homogenous treatment) and the extruded
material obtained from the billet No. 1, respectively.
[0059] On the other hand, the extruded material No. 10 had burning
occurred because of the excessive Si content and had the large
surface roughness.
[0060] The extruded material No. 11 had degraded machinability
because of excessively small Si content.
[0061] In the extruded material No. 12, the number density of
AlFeSi particles exceeded the specific range of the present
invention because of the excessive content of Fe as inevitable
impurity, resulting in large surface toughness (ten-point average
toughness Rz>80 .mu.m). FIGS. 3A and 3B illustrate the scanning
electron micrographs of the billet No. 12 (after the homogenous
treatment) and the extruded material obtained from the billet No.
12, respectively. As shown in FIG. 3A, the amount of .beta.-AlFeSi
phases is large in the billet, causing burning during the extrusion
process, resulting in the large surface roughness.
[0062] In the extruded material of sample No. 13, the number
density of Mg.sub.2Si particles exceeded the specific range of the
present invention, resulting in large surface roughness (ten-point
average roughness Rz>80 .mu.m). FIGS. 4A and 4B illustrate the
scanning electron micrographs of the billet No. 13 (after the
homogenous treatment) and the extruded material obtained from the
billet No. 13, respectively. As shown in FIG. 4A, since the cooling
rate after the homogenization treatment is low, the size of the
Mg.sub.2Si phase in the billet becomes large, causing burning
during the extrusion process, resulting in a large surface
roughness.
[0063] In the extruded material of sample No. 14, the number
densities of AlFeSi particles and Mg.sub.2Si particles exceeded the
respective specific range of the present invention, and in the
extruded material of sample No. 15, the number density of AlFeSi
particles exceeded the specific range of the present invention,
resulting in large surface roughness in both sample No. 14 and No.
15 (ten-point average roughness Rz>80 .mu.m). This is because in
sample No. 14, the time for the homogenization treatment was short,
while in sample No. 15, the temperature of the homogenization
treatment was low, whereby in both samples, the conversion of the
.beta.-AlFeSi particles into a phase did not proceed, and the
division of the Si phase as well as the solid-solution of
Mg.sub.2Si phase in the billet were insufficient.
[0064] In both the extruded materials in samples No. 16 and 17, the
Fe content was excessive, and the number density of AlFeSi
particles exceeded the specific range of the present invention, but
the surface roughness was small (ten-point average roughness
Rz.ltoreq.80 .mu.m). This is because in sample No. 16, the
extrusion rate was set much lower than the lower limit of the
specific range, namely, 3 m/min, while in sample No. 17, the time
for the homogenization treatment was set much longer than the upper
limit of the specific range, namely, 15 hours. In this way, the
productivity in each of samples No. 16 and 17 was degraded.
[0065] In the extruded materials of samples No. 18 and 19, both the
number densities of AlFeSi particles and Mg.sub.2Si particles
satisfied the specific ranges of the present invention, but their
surface roughness were large (ten-point average roughness Rz>80
.mu.m). This is because in sample No. 18, the extrusion temperature
was too high, while in sample No. 19, the extrusion rate was too
high, increasing the material temperature due to the heat
generation during the processing, causing burning in the extruded
material.
[0066] In the extruded material of sample No. 20, the Cu content
was excessive, and thus the extrudability were degraded.
[0067] In the extruded material of sample No. 21, the Mg content
was too small, and thus the strength (hardness) thereof was
low.
[0068] In the extruded material of sample No. 22, the Mg content
was excessive, and the number density of Mg.sub.2Si particles
exceeded the specific range of the present invention, resulting in
a large surface roughness (ten-point average roughness Rz>80
.mu.m). This is considered to be because Mg.sub.2Si phases are
formed in a large amount in the billet due to the excessive Mg
content, causing burning in the extruded material during the
extrusion process.
[0069] The present application claims priority based on Japanese
Patent Application No. 2013-177572 filed on Aug. 29, 2013 and
Japanese Patent Application No. 2014-156634 filed on Jul. 31, 2014,
the disclosures of all of which are incorporated into the present
specification by reference.
* * * * *