U.S. patent application number 14/991183 was filed with the patent office on 2016-05-19 for aluminum alloy brazing sheet for heat exchangers and aluminum alloy brazed article for heat exchangers.
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 Katsuhiro MATSUKADO, Akihiro TSURUNO.
Application Number | 20160138879 14/991183 |
Document ID | / |
Family ID | 43222754 |
Filed Date | 2016-05-19 |
United States Patent
Application |
20160138879 |
Kind Code |
A1 |
MATSUKADO; Katsuhiro ; et
al. |
May 19, 2016 |
ALUMINUM ALLOY BRAZING SHEET FOR HEAT EXCHANGERS AND ALUMINUM ALLOY
BRAZED ARTICLE FOR HEAT EXCHANGERS
Abstract
Disclosed is an aluminum alloy brazing sheet (1) for heat
exchangers, the brazing sheet provided with a core material (2) and
a filler material (3) that comprises an Al--Si--Zn alloy and is
formed on at least one side of the core material (2). The core
material (2) has a pitting potential of -650 mV or more (vs.
Ag/AgCl). The filler material (3) has a zinc concentration of from
1 to 10 percent by mass; a liquid fraction X, at the brazing
temperature, satisfying the relation 0.3.ltoreq.X.ltoreq.0.88; and
a clad ratio d (%) satisfying the relation 15<d.ltoreq.30. The
filler material has a product (X.times.d) of the liquid fraction X
and the clad ratio d (%) satisfying the relation
6.ltoreq.X.times.d).ltoreq.23.
Inventors: |
MATSUKADO; Katsuhiro;
(Moka-shi, JP) ; TSURUNO; Akihiro; (Moka-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: |
43222754 |
Appl. No.: |
14/991183 |
Filed: |
January 8, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13318425 |
Nov 1, 2011 |
|
|
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PCT/JP10/58992 |
May 27, 2010 |
|
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14991183 |
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Current U.S.
Class: |
165/185 |
Current CPC
Class: |
B23K 35/0238 20130101;
F28F 21/084 20130101; B23K 2101/14 20180801; F28F 19/06 20130101;
Y10T 428/12764 20150115; F28F 21/089 20130101; B23K 35/288
20130101; B23K 35/22 20130101; B23K 1/0012 20130101; B23K 35/0233
20130101; C22C 21/02 20130101; C22C 21/00 20130101 |
International
Class: |
F28F 21/08 20060101
F28F021/08; B23K 1/00 20060101 B23K001/00; C22C 21/00 20060101
C22C021/00; C22C 21/02 20060101 C22C021/02; B23K 35/02 20060101
B23K035/02; B23K 35/28 20060101 B23K035/28 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2009 |
JP |
2009-127626 |
Claims
1-6. (canceled)
7: An article comprising a brazed aluminum alloy brazing sheet,
said aluminum alloy brazing sheet comprising: a core material
having a pitting potential of -650 mV (vs. Ag/AgCl) or higher; and
a filler material on at least one side of the core material and
comprising an Al--Si--Zn alloy, wherein the filler material
comprises a Zn content of from 1 to 10 percent by mass, has a
liquid fraction of X at a brazing temperature, and is present in a
clad ratio of d (%), wherein X and d satisfy the conditions:
0.3<X<0.88 and 15<d<30, and wherein the product (XHd)
of the liquid fraction X and the clad ratio d (%) satisfies the
condition: 6<(XHd)<23, wherein the filler material remains as
a residual layer on the core material in the brazed aluminum alloy
brazing sheet, the residual layer has a thickness of 5% or more of
a gauge of the aluminum alloy brazing sheet, and the residual layer
comprises an alpha phase comprising Zn in a content of 1 percent by
mass or more and has an area percentage of 75% or more.
8: The article of claim 7, wherein the filler material of the
aluminum alloy brazing sheet comprises a Zn content of Y by mass
percent and has a thickness of D (.mu.m), and wherein the product
(YHD) of Y and D satisfies the condition: 120<(YHD)<480.
9: The article of claim 7, wherein the filler material of the
aluminum alloy brazing sheet comprises a Mn content of less than
0.05 percent by mass.
10: The article of claim 7, wherein the filler material of the
aluminum alloy brazing sheet comprises a Cu content of 0.05 percent
by mass or more and 0.7 percent by mass or less.
11: The article of claim 7, wherein the core material of the
aluminum alloy brazing sheet comprises a Cu content of 1.5 percent
by mass or less, a Si content of 1.5 percent by mass or less, a Mn
content of 1.8 percent by mass or less, a Ti content of 0.35
percent by mass or less, and a Mg content of 0.5 percent by mass or
less, with the remainder comprising Al and inevitable
impurities.
12: The article of claim 7, which is a heat exchanger.
13: The article of claim 7, which is a heat exchanger for an
automobile.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aluminum alloy brazing
sheet and an aluminum alloy brazed article each for heat
exchangers.
BACKGROUND ART
[0002] Heat exchangers to be mounted in automobiles are formed by
assembling components shaped from brazing sheets and brazing the
assembled components, which brazing sheets each include an aluminum
alloy core material clad with a filler material. Gauge down of such
aluminum alloy brazing sheets for heat exchangers, typically for
tube members, have been proceeded from a customary thickness of
0.3-0.5 mm to 0.2 mm or less for the purpose of weight reduction of
the heat exchangers. Along with this, the aluminum alloy brazing
sheets should have higher strength and better corrosion resistance.
The weight reduction of a heat exchanger may be possible by
employing a tube member composed of the aluminum alloy brazing
sheet having a filler material facing outward, in combination with
a fin member (bare fin) containing no filler material. This heat
exchanger, however, is difficult to exhibit sufficient corrosion
resistance when the filler-clad surface of the tube member, which
is clad with the filler material to be joined with the fin member,
is exposed to a corrosive environment.
[0003] To solve the problem, Patent Literature (PTL) 1 discloses an
aluminum alloy brazing sheet which includes a core material and,
present thereon, a filler material, which core material is composed
of an Al--Mn alloy, and which filler material is composed of an
Al--Si alloy containing Si in a content of 7.0 to 11.0 percent by
mass and further containing Zn in a content of 1.0 to 7.0 percent
by mass. The aluminum alloy brazing sheet is intended to improve
its corrosion resistance by allowing part of Zn in the filler
material to migrate into the surface layer of the core material
during a brazing process and thereby allowing the surface of the
component after brazing to have a less novel potential to impart a
sacrificial effect to the component.
[0004] PTL 1: Japanese Unexamined Patent Application Publication
(JP-A) No. H07-331372 (claims 1 and 2, paragraphs 0005, 0009, and
0010)
DISCLOSURE OF INVENTION
Technical Problem
[0005] According to the technique disclosed in PTL 1, however, Zn
migrates little from the filler material into the core material
during the brazing process, most of the filler material melts and
fluidizes during the brazing process, and, after brazing, only
little amount of the filler material remains on the surface of the
member (core material) and only little amount of Zn is contained
therein. Independently, this technique recommends to add less than
0.5 percent by mass of Cu to the core material, so as to allow the
core material to have a more noble potential. However, the brazing
process causes elements to migrate also from the core material into
the filler material, and this causes a brazing filler layer (braze
layer) containing a large amount of Cu to remain on the surface of
the core material. This makes it difficult to allow the surface
layer of the aluminum alloy brazing sheet after the brazing
process, i.e., the surface layer of the core material, to have a
sufficient potential difference with respect to the inside thereof
in a thickness direction to thereby impart a sacrificial effect
thereto. The surface layer, if exposed to a severe corrosive
environment, may suffer from generation of through holes in early
stages. In addition, most of Zn is contained in the filler
material, which has fluidized during the brazing process, and a
fillet formed by the fluidized filler contains Zn in a
concentration higher than that of the surface of the aluminum alloy
brazing sheet after brazing and is thereby susceptible to
preferential corrosion. This may cause delamination at a brazed
joint of the heat exchanger and may thereby cause falling of fins
or spill of a coolant due to due to perforation corrosion of
tubes.
[0006] Accordingly, an object of the present invention is to
provide an aluminum alloy brazing sheet for heat exchangers which
has satisfactory brazability and gives, after brazing, a
filler-clad surface and a fillet each being satisfactorily
resistant to corrosion.
Solution to Problem
[0007] To achieve the object, the present inventors have invented
an aluminum alloy brazing sheet for heat exchangers which exhibits
a satisfactory sacrificial effect, i.e., good corrosion resistance.
This is achieved by controlling the contents of Zn and other
elements contained in the filler material, controlling the liquid
fraction of the filler material at a brazing temperature, and
controlling the clad ratio (or thickness) of the filler material,
thereby allowing only part of the filler material in the brazing
process to allow the residue of the filler material to remain on
the core material, and allowing the residual layer (residual filler
layer) to function as a sacrificial layer. The present inventors
have also invented an aluminum alloy brazing sheet for heat
exchangers which gives a fillet being resistant to preferential
corrosion, having good corrosion resistance satisfactorily
maintained, and having a sufficient size to give a higher joint
strength.
[0008] Specifically, the present invention provides an aluminum
alloy brazing sheet for heat exchanges, which includes a core
material; and a filler material being present on at least one side
of the core material and including an Al--Si--Zn alloy, in which
the core material has a pitting potential of -650 mV (vs. Ag/AgCl)
or higher, and the filler material has a Zn content of from 1 to 10
percent by mass, has a liquid fraction of X at a brazing
temperature, and is present in a clad ratio of d (%), where X and d
satisfy the conditions: 0.3.ltoreq.X.ltoreq.0.88 and
15<d.ltoreq.30, and the product (X.times.d) of the liquid
fraction X and the clad ratio d (%) satisfies the condition:
6.ltoreq.(X.times.d).ltoreq.23.
[0009] The configuration allows the filler material to remain in a
specific amount on the core material and, simultaneously, to form a
fluidized filler in a specific amount, because the filler material
contains a predetermined element in a specific amount, has a
predetermined liquid fraction, and is present in a predetermined
clad ratio. This allows a brazing filler alloy containing Zn in a
suitable concentration to remain on the core material having a
pitting potential of -650 mV (vs. Ag/AgCl) or higher after brazing
and thereby gives a satisfactory potential difference between the
surface portion (residual filler layer) and the inner portion (core
material) after brazing. As the thus-given potential difference
between the surface portion and the inner portion is large, the
sacrificial effect can be exhibited sufficiently by arranging the
residual filler layer on a side to face a corrosive environment.
Independently, in brazing, the fluidized filler derived from the
filler material and the residue (remainder) thereof are allowed to
have Zn concentrations being not so different from each other, this
allows the residue (i.e., the residual filler layer) and the
fluidized filler to have substantially identical potentials and
thereby suppresses the preferential corrosion of the fillet. The
aluminum alloy brazing sheet having the configuration according to
the present invention can have both satisfactory brazability and
good post-brazing corrosion resistance (corrosion resistance both
of the surface and of the fillet).
[0010] In the aluminum alloy brazing sheet for heat exchangers, the
filler material preferably has a Zn content of Y (percent by mass)
and a thickness of D (.mu.m), in which the product between them
(Y.times.D) satisfies the condition:
120.ltoreq.(Y.times.D).ltoreq.480.
[0011] This configuration enables suitable control of the Zn
concentrations of the residual filler layer and fillet after
brazing, typically even when the filler material has a thickness
which varies corresponding to the gauge of the brazing sheet.
[0012] In the aluminum alloy brazing sheet for heat exchangers, the
filler material preferably has a Mn content controlled to be less
than 0.05 percent by mass. The aluminum alloy brazing sheet having
this configuration gives a molten filler with higher fluidity and
provides satisfactory brazability, because the filler material has
a Mn content of less than 0.05 percent by mass.
[0013] In the aluminum alloy brazing sheet for heat exchangers, the
filler material may further contain Cu in a content of 0.05 percent
by mass or more and 0.7 percent by mass or less. After brazing, Cu
derived from the filler material is contained in a larger amount in
the fillet, and this improves the corrosion resistance of the
brazed joint without impairing the sacrificial effect of the
residual filler layer.
[0014] In the aluminum alloy brazing sheet for heat exchangers, the
core material preferably contains Cu in a content of 1.5 percent by
mass or less, Si in a content of 1.5 percent by mass or less, Mn in
a content of 1.8 percent by mass or less, Ti in a content of 0.35
percent by mass or less, and Mg in a content of 0.5 percent by mass
or less, with the remainder being Al and inevitable impurities. The
aluminum alloy brazing sheet for heat exchangers having this
configuration may have higher strength, better brazability, and
better corrosion resistance, because the core material contains
predetermined elements in specific amounts.
[0015] The present invention further provides an aluminum alloy
brazed article for heat exchangers, obtained from the aluminum
alloy brazing sheet for heat exchangers through a brazing process,
in which the filler material after the brazing process remains as a
residual layer on the core material, the residual layer has a
thickness of 5% or more of the gauge of the aluminum alloy brazing
sheet for heat exchangers, and the residual layer comprises an
alpha phase containing Zn in a content of 1 percent by mass or more
and being present in an area percentage of 75% or more.
[0016] The aluminum alloy brazing sheet for heat exchangers having
this configuration can have satisfactory corrosion resistance. This
is because the aluminum alloy brazed article is obtained from the
aluminum alloy brazing sheet for heat exchangers through brazing,
the filler material after brazing remains as a residual layer on
the core material, the residual layer has a thickness of 5% or more
of the gauge of the aluminum alloy brazing sheet for heat
exchangers, and the residual layer includes an alpha phase
containing Zn in a content of 1 percent by mass or more and being
present in an area percentage of 75% or more, and this gives a
sufficient potential difference between the residual layer
(residual filler layer) and the core material.
Advantageous Effects of Invention
[0017] The present invention provides an aluminum alloy brazing
sheet for heat exchangers which has satisfactory brazability and
gives a filler-clad surface and a fillet both with good corrosion
resistance. The present invention also provides an aluminum alloy
brazed article for heat exchangers, using the aluminum alloy
brazing sheet for heat exchangers.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIGS. 1(a) and 1(b) are cross-sectional views schematically
illustrating the structures of an aluminum alloy brazing sheet for
heat exchangers and an aluminum alloy brazed article for heat
exchangers, respectively, according to embodiments of the present
invention.
[0019] FIG. 2 depicts schematic views of an aluminum alloy brazed
article for heat exchangers used for the evaluation of brazability
and corrosion resistance of a joint in experimental examples below,
in which the views (a) and (b) are a perspective view before
brazing and a front view of the aluminum alloy brazed article,
respectively.
[0020] FIG. 3 depicts schematic views of an aluminum alloy brazed
article for heat exchangers for the evaluation of brazability and
corrosion resistance of a joint in experimental examples, in which
the views (a) and (b) are a perspective view before brazing and a
cross-sectional view of the essential parts thereof of the aluminum
alloy brazed article, respectively.
REFERENCE SIGNS LIST
[0021] 1 aluminum alloy brazing sheet for heat exchangers (brazing
sheet) [0022] 10 aluminum alloy brazed article for heat exchangers
(aluminum alloy brazed article) [0023] 2 core material [0024] 3
filler material [0025] 30 residual filler layer
BEST MODES FOR CARRYING OUT THE INVENTION
[0026] Embodiments of an aluminum alloy brazing sheet for heat
exchangers and an aluminum alloy brazed article for heat exchangers
according to the present invention will be illustrated below.
[Brazing Sheet]
[0027] An aluminum alloy brazing sheet for heat exchangers (brazing
sheet) 1 according to an embodiment of the present invention
includes two layers, i.e., a core material (layer) 2, and a filler
material (layer) 3 present on one side of the core material 2, as
illustrated in FIG. 1(a).
[0028] The aluminum alloy brazing sheet for heat exchangers
according to the present invention is brazed at a predetermined
brazing temperature by a known procedure to give an aluminum alloy
brazed article for heat exchangers according to the present
invention, and the brazed article is used in a heat exchanger.
Specifically, the brazing sheet 1 according to one embodiment is
formed into a shape of a desired component such as a tube or plate;
a flux is applied to a surface of the filler material 3 to remove
an oxide film on the surface; this component is assembled with
another piece thereof or another aluminum or aluminum alloy
component, held at a predetermined brazing temperature for brazing,
and thereby yields an aluminum alloy brazed article for heat
exchangers (aluminum alloy brazed article) 10 according to another
embodiment of the present invention, as illustrated in FIG. 1(b).
The brazing process causes the filler material 3 to melt or fuse,
part of which fluidizes and forms a fillet (not shown) at a joint
in the aluminum alloy brazed article 10, and the residue of which
remains on the core material 2 and forms a residual filler layer
(residual braze layer) 30.
[0029] Though not critical, the brazing sheet 1 preferably has a
gauge (thickness) of from 0.12 to 0.5 mm when adopted to a tube
member of a heat exchanger. Independently, the brazing sheet 1
preferably has a gauge of from 0.8 to 2.0 mm when adopted to a
plate member of a heat exchanger. The contents of respective
elements and other conditions of the core material 2 and the filler
material 3 constituting the brazing sheet 1 according to this
embodiment will be illustrated in detail below.
[Core Material]
[0030] The core material 2 has a pitting potential of -650 mV (vs.
Ag/AgCl) or higher. The core material 2 is not limited, as long as
being an aluminum alloy having such a pitting potential, but is
preferably an aluminum alloy containing Cu in a content of 1.5
percent by mass or less and is more preferably an aluminum alloy
further containing Si in a content of 1.5 percent by mass or less,
Mn in a content of 1.8 percent by mass or less, Ti in a content of
0.35 percent by mass or less, and Mg in a content of 0.5 percent by
mass or less, each with the remainder being Al and inevitable
impurities. The pitting potential and the aluminum alloy chemical
composition herein are those of a material for the core material 2
in the manufacturing of the brazing sheet 1. Though not critical,
the core material 2 has a thickness of preferably from 0.05 to 1.2
mm.
[0031] (Pitting Potential: -650 mV (Vs. Ag/AgCl) or Higher)
[0032] The core material 2, as having a pitting potential of -650
mV (vs. Ag/AgCl) or higher (more noble), gives a sufficient
potential difference between the core material 2 and the residual
filler layer 30 in the aluminum alloy brazed article 10 after
brazing and thereby provides a satisfactory sacrificial effect
(good corrosion resistance). As used herein the phrase "pitting
potential of -650 mV or higher" refers to a pitting potential of
-650 mV or higher in a positive direction, namely, a pitting
potential having an absolute value of 650 mV or less. Specifically,
with a more positive pitting potential (with a smaller absolute
value thereof), the aluminum alloy has a more noble potential. As
used herein the indication "(vs. Ag/AgCl)" means that the potential
is a value measured with reference to a silver-silver chloride
electrode. In contrast, the core material 2, if having a pitting
potential of lower than (less noble than) -650 mV (vs. Ag/AgCl), is
difficult to give a sufficient potential difference. The core
material 2 may have a more noble potential by adding elements such
as Cu, as described later. However, the core material 2 preferably
has a pitting potential of lower than (less noble than) -500 mV.
This is because, if the core material 2 has a more noble pitting
potential of -500 mV or higher typically by the addition of Cu, Cu
is present in excess, and this causes a lower melting point of the
core material 2 or inferior workability of the brazing sheet; or Cu
migrates into the filler material 3 to cause the residual filler
layer 30 to have a more noble potential, resulting in an
insufficiently large potential difference. As used herein the
"pitting potential" is defined as such a potential that a current
density in an anode polarization curve in a 5% NaCl aqueous
solution (pH 3) at 25.degree. C. be 10.sup.-4 A/cm.sup.2.
[0033] (Cu Content: 1.5 Percent by Mass or Less)
[0034] Copper (Cu) helps the aluminum alloy to have a more noble
potential and thereby helps the core material 2 to have better
corrosion resistance. In addition, Cu also helps the core material
2 to have a higher post-brazing strength (strength of the aluminum
alloy brazed article 10). For exhibiting the effects sufficiently,
the core material 2 preferably has a Cu content of 0.2 percent by
mass or more. In contrast, if the Cu content be more than 1.5
percent by mass, silicon (Si) and other elements may migrate from
the filler material 3 into the core material 2 to cause local
increase in alloy element concentrations, and this may cause the
core material 2 to undergo local fusion during brazing process at a
temperature lower than the melting point of the matrix of the core
material 2. To avoid this, the core material 2 has a Cu content of
preferably 1.5 percent by mass or less, and more preferably 0.9
percent by mass or less.
[0035] (Si Content: 1.5 Percent by Mass or Less)
[0036] Silicon (Si) helps the core material 2 to have a higher
post-brazing strength and, particularly when coexisting with Mg and
Mn, forms Mg--Si intermetallic compounds and Al--Mn--Si
intermetallic compounds, and thereby helps the core material 2 to
have a further higher post-brazing strength. For exhibiting the
effects sufficiently, the core material 2 preferably has a Si
content of 0.3 percent by mass or more. In contrast, the core
material 2, if having a Si content of more than 1.5 percent by
mass, may have a lower melting point, may include increased amounts
of low-melting-point phases, and may thereby become more fusible
(meltable). To avoid this, the core material 2 has a Si content of
preferably 1.5 percent by mass or less and more preferably 1.2
percent by mass or less.
[0037] (Mn Content: 1.8 Percent by Mass or Less)
[0038] Manganese (Mn) helps the core material 2 to have a higher
post-brazing strength, and, with an increasing Mn content, the core
material 2 has an increasing post-brazing strength. In addition, Mn
helps the aluminum alloy to have a more noble potential and thereby
helps the core material 2 to exhibit better corrosion resistance.
For exhibiting the effects sufficiently, the core material 2
preferably has a Mn content of 0.5 percent by mass or more. In
contrast, the core material 2, if having a Mn content of more than
1.8 percent by mass, may undergo the generation of coarse
intermetallic compounds and may thereby have inferior formability
(this means the brazing sheet 1 may have inferior formability) and
may often have insufficient corrosion resistance. To avoid these,
the core material 2 preferably has a Mn content of 1.8 percent by
mass or less.
[0039] (Ti Content: 0.35 Percent by Mass or Less)
[0040] Titanium (Ti) forms a Ti--Al compound which has a more noble
potential among aluminum alloys. The Ti--Al compound is present in
a laminar distribution, and this renders corrosion be in a layered
form and thereby suppresses the corrosion to proceed in a depth
direction. For exhibiting the effects sufficiently, the core
material 2 preferably has a Ti content of 0.05 percent by mass or
more. In contrast, the core material 2, if having a Ti content of
more than 0.35 percent by mass, may suffer from the generation of
coarse intermetallic compounds, may thereby have inferior
formability (this means the brazing sheet 1 may have inferior
formability), and may often have insufficient corrosion resistance.
To avoid these, the core material 2 preferably has a Ti content of
0.35 percent by mass or less.
[0041] (Mg Content: 0.5 Percent by Mass or Less)
[0042] Magnesium (Mg) helps the core material 2 to have a higher
post-brazing strength. For exhibiting the effects sufficiently, the
core material 2 preferably has a Mg content of 0.05 percent by mass
or more. In contrast, Mg, if present in the core material 2 in a
content of more than 0.5 percent by mass, may migrate into the
filler material 3 in the brazing process to react with a flux
(K--Al--F flux) coated on the surface of the filler material 3 in
the brazing sheet 1, and this may reduce the effect of the flux and
thereby often impair the brazability of the brazing sheet 1. To
avoid these, the core material 2 preferably has a Mg content of 0.5
percent by mass or less.
[0043] (Inevitable Impurities)
[0044] The core material 2 may further contain other elements such
as Fe, Cr, and Pb as inevitable impurities, in addition to the
above composition. Specifically, these elements may be regarded as
inevitable impurities, as long as Fe is present in a content of 0.5
percent by mass or less; Cr and Pb are present in contents of each
0.3 percent by mass or less; and these elements are present in a
total content of 1.0 percent by mass or less.
[Filler Material]
[0045] The filler material (brazing filler material) 3 includes an
Al--Si--Zn alloy, has a Zn content of from 1 to 10 percent by mass,
has a liquid fraction of X at a brazing temperature, and is present
in a clad ratio of d (%), in which X and d satisfy the conditions:
0.3.ltoreq.X.ltoreq.0.88 and 15.ltoreq.d.ltoreq.30, and the product
(X.times.d) of the liquid fraction X and the clad ratio d (%)
satisfies the condition: 6.ltoreq.(X.times.d).ltoreq.23.
Specifically, the filler material 3 is arranged in the brazing
sheet 1 at a clad ratio of more than 15% but 30% or less. The
chemical composition, such as the Zn content, of the Al--Si--Zn
alloy and the liquid fraction are values of a material for the
filler material 3 in the manufacture of the brazing sheet 1. After
the brazing process of the brazing sheet 1, namely, in the aluminum
alloy brazed article 10, the filler material 3 forms a fillet at a
joint and also forms a residual filler layer 30 on the core
material 2 (see FIG. 1(b)) to function as a sacrificial layer.
[0046] (Al--Si--Zn Alloy)
[0047] Silicon (Si) significantly helps the aluminum alloy to have
a lower melting point, thereby helps the filler material 3 to have
a higher liquid fraction and to have more satisfactory filler
fluidity at a temperature in the brazing process (brazing
temperature) of the brazing sheet 1 according to the present
invention. Independently, Zn helps the aluminum alloy to have a
less noble potential, to have a lower melting point, and to thereby
have a higher liquid fraction. The filler material 3 preferably has
a Si content of from 3 to 8 percent by mass. The filler material 3,
if having a Si content of more than 8 percent by mass, may cause
decrease of an alpha phase which remains without an eutectic
reaction with Si. For example, when brazing is performed at a
brazing temperature of 600.degree. C. and at a Si content of 8
percent by mass and a Zn content of 1 percent by mass, the filler
material 3 has a liquid fraction of more than 0.88, and the
residual filler layer 30 may fail to include a sufficient amount of
the alpha phase. For ensuring the residual filler in a sufficient
amount and for allowing the residual filler layer 30 to function as
a sacrificial layer having a suitable thickness, the filler
material 3 more preferably has a Si content of 7.5 percent by mass
or less. In contrast, the filler material 3, if having a Si content
of less than 3 percent by mass, may have an excessively low liquid
fraction, and this may reduce the amount of the fluidized filler
and may impede the formation of a fillet with a sufficient size.
For sufficient brazability, the filler material 3 more preferably
has a Si content of 5 percent by mass or more. Accordingly, the
filler material 3 more preferably has a Si content of from 5 to 7.5
percent by mass.
[0048] (Zn Content: 1 Percent by Mass or More and 10 Percent by
Mass or Less)
[0049] As is described above, Zn helps the aluminum alloy to have a
less noble potential, and, as with Si, helps the aluminum alloy to
have a lower melting point. The filler material 3, if having a Zn
content of less than 1 percent by mass, causes the residual filler
layer on the surface of the core material 2 after brazing to
contain Zn in a less amount and to have insufficient sacrificial
effect. In contrast, the filler material 3, if having a Zn content
of more than 10 percent by mass, causes the fluidized filler to
contain Zn in a larger amount (in a higher Zn concentration) and
thereby causes preferential corrosion. For giving a fillet with
good corrosion resistance, the filler material 3 preferably has a
Zn content of 6 percent by mass or less. For these reasons, the
filler material 3 has a Zn content of 1 percent by mass or more and
10 percent by mass or less, and preferably has a Zn content of 6
percent by mass or less for giving a fillet with better corrosion
resistance. The filler material 3 may have a Zn content larger than
its Si content. Both Si and Zn help the aluminum alloy to have a
lower melting point and to have a higher liquid fraction.
Accordingly, the amounts (contents) of these elements are
preferably determined through thermodynamic calculations as
described later, so that the filler material 3 has a liquid
fraction of 0.3 or more and 0.88 or less at the brazing
temperature.
[0050] (Liquid fraction at brazing temperature: 0.3 or more and
0.88 or less) The filler material 3 may melt (fuse) and fluidize in
a less amount by allowing the filler material 3 to have a liquid
fraction of less than 1 at the brazing temperature. Specifically,
at the brazing temperature, which is equal to or higher than the
eutectic temperature of the Al--Si alloy, a customary filler
material mostly melts and fluidizes because of having a liquid
fraction of approximately 1; but in contrast to this, part of the
filler material (layer) 3 melts and fluidizes as a result of an
eutectic reaction between the alpha phase and a silicon phase, but
the residue (portion not reacted with the eutectic silicon) remains
as an alpha phase on the core material 2 to form a residual filler
layer 30. The filler material 3, if having a liquid fraction of
less than 0.3 at the brazing temperature, fails to give a fluidized
filler in a sufficient amount and fails to exhibit sufficient
brazability. In contrast, the filler material 3, if having a liquid
fraction of more than 0.88, causes the residual filler layer 30
functioning as a sacrificial layer to be present in a less amount
and to fail to provide sufficient corrosion resistance. To avoid
these, the filler material 3 has a liquid fraction at the brazing
temperature of 0.3 or more and 0.88 or less, and preferably 0.5 or
more and 0.8 or less. The liquid fraction of the filler material 3
is controlled within the range so that the product of the liquid
fraction and the clad ratio (%) be 6 or more and 23 or less.
[0051] The liquid fraction of the filler material 3 is determined
by the brazing temperature and the chemical composition of the
aluminum alloy (Al--Si--Zn alloy) constituting the filler material
3. The brazing temperature of the brazing sheet 1 according to the
present invention is not critical, as long as being a temperature
employed in a regular brazing process using an Al--Si alloy as a
filler material. Specifically, the brazing temperature may be a
temperature equal to or higher than the eutectic temperature
(577.degree. C.) of the Al--Si alloy and lower than the melting
temperature (solidus temperature) of the aluminum alloy
constituting the core material 2. More specifically, the brazing
temperature preferably falls within the range of from 580.degree.
C. to 620.degree. C. Within this range, the brazing temperature may
be set to such a temperature that the Al--Si--Zn alloy constituting
the filler material 3 has a liquid fraction of 0.3 or more and 0.88
or less. With increasing contents of Si and Zn, the melting point
of the Al--Si--Zn alloy decreases, namely, the brazing temperature
to be set decreases, or the liquid fraction at a certain brazing
temperature rises. These are more significantly affected by the Si
content. In addition, the melting point of the Al--Si--Zn alloy
also falls by the addition of Cu. Accordingly, it is desirable to
determine the contents of respective elements, particularly the Si
and Zn contents, of the Al--Si--Zn alloy constituting the filler
material 3 so that they fall within the above ranges and so that
the filler material 3 has a liquid fraction of 0.3 or more and 0.88
or less at a desired brazing temperature. The liquid fraction of
the filler material 3 at a brazing temperature is a value as
calculated from the composition (for example, Si and Zn contents)
of the Al--Si--Zn alloy as a material for the filler material 3
using a standard thermodynamic calculation software such as the
Thermo-Calc (trade name, supplied by Thermo-Calc Software AB).
[0052] (Clad Ratio: More than 15% but 30% or Less)
[0053] The filler material 3, if present in a clad ratio of 15% or
less, may not give a fluidized filler in a sufficient amount during
the brazing process and may exhibit insufficient brazability, even
when the filler material 3 has a high liquid fraction of 0.88,
i.e., its upper limit. In contrast, the filler material 3, if
present in a clad ratio of more than 30%, has an excessively high
liquid fraction. In this case, if the product of the clad ratio and
the liquid fraction is larger than a specific level as described
later, an excessive fluidized filler may erode the core material 2
to cause local corrosion; or when the filler material 3 has a not
so high liquid fraction, the residual filler layer 30 after brazing
becomes excessively thick, and this causes significant gauge down
by corrosion and thereby causes the aluminum alloy brazed article
10 to have a decreasing strength with time. In contrast, the filler
material 3, if being present in a clad ratio of more than 30% and
having a low liquid fraction, may cause a low density of eutectic
silicon and may thereby increase the amount of a filler not
contributing to fluidization even when the filler material 3 melts
as a result of the eutectic reaction, resulting in insufficient
brazability. To avoid these, the filler material 3 is present in a
clad ratio of more than 15% but 30% or less. As specified herein
the clad ratio of the filler material 3 refers to a clad ratio per
one side (one layer).
[0054] (Product of Liquid Fraction and Clad Ratio (%): 6 or More
and 23 or Less)
[0055] In the brazing sheet 1 according to the present invention,
part of the filler material 3 is prevented from melting and
fluidizing upon brazing, because of a low liquid fraction (less
than 1) of the filler material 3. Accordingly, it is necessary to
control the amount of the fluidized filler to such an amount as to
give suitable brazability. Specifically, the amount of the
fluidized filler is controlled to such an amount as to be
sufficient to join a member but not to erode the member (the core
material 2). Of the filler material 3 being present in the brazing
sheet 1 in a clad ratio (%) of d and having a liquid fraction of X,
the clad ratio of substantial filler material which acts as a
fluidized filler in the brazing process is expressed by the product
(X.times.d) of the liquid fraction and the clad ratio of the filler
material 3. According to the present invention, not only the clad
ratio and liquid fraction of the filler material 3 are controlled
respectively within specific ranges, but also the clad ratio of the
substantial filler material is controlled. The filler material 3,
if having a clad ratio of substantial filler material X.times.d of
less than 6, gives a fluidized filler in an insufficient amount and
thereby fails to exhibit sufficient brazability. In contrast, the
filler material 3, if having a clad ratio of substantial filler
material X.times.d of more than 23, gives a fluidized filler in an
excessively large amount, and this erodes the member. To avoid
these, the filler material 3 has a product X.times.d of the liquid
fraction X and the clad ratio d (%) of 6 or more and 23 or less
(6.ltoreq.(X.times.d).ltoreq.23), and the liquid fraction X and the
clad ratio d are to be set within the specific ranges
(0.3.ltoreq.X.ltoreq.0.88, 15<d.ltoreq.30) so that the product
falls in the above-specified range.
[0056] (Product of Zn Content (Percent by Mass) and Thickness
(.mu.m) of Filler Material: 120 or More and 480 or Less)
[0057] The Al--Si--Zn alloy constituting the filler material 3
contains Zn in a content as specified above. Part of the Zn
migrates from the filler material 3 into the core material 2 by the
action of hot rolling and annealing in manufacturing processes of
the brazing sheet 1, and of heating during the brazing process.
Accordingly, the Zn concentration of the filler material 3 in the
brazing process is lower than the Zn content. Hereinafter when
simply referred to as the "Zn content" of the filler material 3, it
refers to the Zn content of the Al--Si--Zn alloy. Particularly when
the filler material 3 is thin, the filler material 3 contains Zn in
a small absolute amount, and this causes Zn to migrate into the
core material 2 in a further larger relative amount and to remain
in the filler material 3 in a further smaller relative amount (in a
further smaller concentration). The resulting filler material 3
having a further smaller Zn concentration forms a residual filler
layer 30, and the residual filler layer 30 thereby has a Zn
concentration lower than the Zn content of the filler material 3.
The residual filler layer 30, if having a low Zn concentration, may
exhibit insufficient sacrificial effect. For having the Zn
concentration at a satisfactory level, it is desirable to control
the Zn content of the filler material 3 according to the thickness
thereof. The amount of Zn per unit area of the brazing sheet 1 may
be indicated by [Zn].times.D, in which [Zn] represents the Zn
content (percent by mass) of the filler material 3; and D
represents the thickness of the filler material 3. Namely, it is
desirable to control the product of the Zn content [Zn] of the
filler material 3 and the thickness D of the filler material 3.
More specifically, the product [Zn].times.D of the Zn content
[Zn](percent by mass) of the filler material 3 and the thickness D
(.mu.m) of the filler material 3 is preferably controlled to 120 or
more and 480 or less (120.ltoreq.([Zn].times.D).ltoreq.480). The
thickness of the filler material 3 is determined by the gauge of
the brazing sheet 1 and the clad ratio of the filler material 3.
However, even when the brazing sheet 1 has a small gauge, the
filler material 3 preferably has a thickness of 25 .mu.m or
more.
[0058] (Mn Content: Less than 0.05 Percent by Mass)
[0059] The filler material 3 preferably has a minimized or lowered
Mn content, because Mn causes the brazing metal (filler) as a melt
of the Al--Si (--Zn) alloy to have lower fluidity. Specifically, by
controlling the Mn content to less than 0.05 percent by mass, the
molten filler may have satisfactory fluidity and may exhibit
satisfactory brazability even in joining of a component having a
complicated shape.
[0060] (Cu Content: 0.05 Percent by Mass or More and 0.7 Percent by
Mass or Less)
[0061] The filler material 3 may further contain Cu. Copper (Cu)
helps the aluminum alloy to have a more noble potential as
described above and exhibits a contradictory action to the action
of Zn in the filler material 3. In the brazing process of the
brazing sheet 1 according to the present invention, the filler
material 3 is present as two phases, i.e., a solid-phase alpha
phase (Al containing Zn as a solid solution) and a liquid-phase
molten Al--Si--Zn alloy, because of having a liquid fraction of
less than 1 at the brazing temperature. The other elements or
compounds are distributed to the respective phases according to
their properties. For example, Cu, when contained in the Al--Si--Zn
alloy constituting the filler material 3, is distributed in a
larger amount into the liquid phase than into the alpha phase,
because an Al--Cu alloy is an eutectic alloy. Most of the liquid
phase fluidizes, whereby the residual filler layer 30, which has
been formed mainly from the alpha phase remaining on the surface of
the aluminum alloy brazed article 10 (the core material 2) after
the brazing process, has a relatively low Cu concentration, thereby
has a not so more noble potential, and surely exhibits satisfactory
corrosion resistance without significant deterioration in
sacrificial effect. In contrast, the fillet, which has been formed
from the liquid phase, i.e., from the fluidized filler, has a
relatively high Cu concentration, and this helps the joint to have
more satisfactory corrosion resistance and thereby further protects
the joint from delamination due to corrosion. For exhibiting the
effects sufficiently, the filler material 3 has a Cu content of
preferably 0.05 percent by mass or more and more preferably 0.1
percent by mass or more. In contrast, the filler material 3, if
having a Cu content of more than 0.7 percent by mass, causes the
alpha phase, to which Cu has been distributed in a relatively small
amount, to have a higher Cu concentration, and this may cause the
residual filler layer 30 to have a higher Cu concentration and to
exhibit an insufficient sacrificial effect. For these reasons, the
filler material 3 has a Cu content of preferably 0.7 percent by
mass or less and more preferably 0.4 percent by mass or less. In
addition, the filler material 3 preferably has a Cu content of
equal to or less than the Cu content of the core material 2, more
preferably has a Cu content of less than that of the core material
2 by 0.2 percent by mass or more, and more preferably has a Cu
content of less than that of the core material 2 by 0.3 percent by
mass or more.
[0062] The Al--Si--Zn alloy constituting the filler material 3 may
further suitably contain one or more elements allowing the aluminum
alloy to have a less noble potential, such as In and Sn, in
addition to the above elements. In addition or alternatively, the
aluminum alloy may further contain Fe and other elements within
ranges not adversely affecting the advantageous effects of the
present invention. Specifically, the Al--Si--Zn alloy may contain
these elements without adversely affecting the advantageous effects
of the present invention, as long as it contains Fe in a content of
0.5 percent by mass or less and other elements each in a content of
0.3 percent by mass or less, in which the total content of these
elements is 1.0 percent by mass or less.
[0063] With reference to FIG. 1(a), the brazing sheet 1 according
to this embodiment has a two-layer structure including the core
material 2 and, present on one side thereof, the filler material 3,
but the structure of the brazing sheet is not limited thereto.
Specifically, in another embodiment of the present invention, an
aluminum alloy brazing sheet may have a three-layer structure
including a core material 2; a filler material 3 present on one
side of the core material 2; and a second filler material present
on the other side of the core material 2. The second filler
material present on the other side may be formed from an Al--Si--Zn
alloy as with the filler material 3 to function as a sacrificial
layer after the brazing process, or may be formed from a common
Al--Si alloy as a filler material, such as a 4000-series aluminum
alloy. In yet another embodiment, an aluminum alloy brazing sheet
may have a three-layer structure including a core material 2; a
filler material 3 present on one side of the core material 2; and a
sacrificial anode material present on the other side of the core
material 2. The sacrificial anode material may be a material
commonly used as a sacrificial anode material, such as a
1000-series aluminum or a 7000-series aluminum alloy. In still
another aspect, an aluminum alloy brazing sheet may have a
four-layer structure including an intermediate material between the
core material 2 and the second filler material. The intermediate
material may be a regular material composed typically of a
1000-series aluminum or a 7000-series aluminum alloy.
[Aluminum Alloy Brazed Article]
[0064] An aluminum alloy brazed article for heat exchangers
(aluminum alloy brazed article) 10 according to another embodiment
of the present invention is formed from the brazing sheet 1
according to the embodiment through a brazing process at a
predetermined brazing temperature and constitutes a heat exchanger.
In the aluminum alloy brazed article 10, the filler material 3 of
the brazing sheet 1 remains on the core material 2 while having a
thickness of 5% or more of the gauge of the brazing sheet 1 before
brazing. The residual layer, i.e., the residual filler layer 30
(see FIG. 1(b)) includes an alpha phase containing Zn in a content
of 1 percent by mass or more and being present in an area
percentage of 75% or more. As used herein the term "area
percentage" of the alpha phase refers to an area percentage in a
cross section of the aluminum alloy brazed article 10. Also as used
herein the phrase "alpha phase containing Zn in a content of 1
percent by mass or more" means that the alpha phase has a Zn
content of 1 percent by mass or more. Hereinafter the residual
filler layer 30 will be described.
[0065] (Thickness of Residual Filler Layer: 5% or More of Gauge of
Brazing Sheet Before Brazing)
[0066] The residual filler layer 30 functions as a sacrificial
layer for the core material 2 in the aluminum alloy brazed article
10, and thereby has a longer anti-corrosion life with an increasing
thickness thereof. The residual filler layer 30 if having a
thickness of less than 5% of the gauge of the brazing sheet 1
before brazing, does not reliably have a sufficient anti-corrosion
life. To avoid this, the residual filler layer 30 should have a
thickness of 5% or more of the gauge of the brazing sheet 1 before
brazing.
[0067] (Area Percentage of Alpha Phase in Residual Filler Layer:
75% or More)
[0068] With reference to FIG. 1(b), the residual filler layer 30 is
composed of an alpha phase (Al containing Zn as a solid solution)
and an eutectic phase, in which the alpha phase has not been
reacted with Si through an eutectic reaction and has not molten
during brazing, and the eutectic phase is a portion of the molten
liquid phase (Al--Si--Zn) which portion remains on the core
material 2 without fluidizing out from the core material 2 and is
solidified. The eutectic phase contains a large amount of Si,
causes the aluminum alloy to have a more noble potential, and, when
contained in a large amount in the residual filler layer 30, causes
the residual filler layer 30 to exhibit an insufficient sacrificial
effect. The eutectic phase formed by solidification of a fluidized
liquid phase (fluidized filler) forms a fillet at a joint in the
aluminum alloy brazed article 10. Accordingly, the residual filler
layer 30 preferably contains a residual eutectic phase in a small
amount, i.e., contains an alpha phase in a large amount, in order
to give a fillet of large size. Specifically, the residual filler
layer 30, if being present in an area percentage of the alpha phase
of less than 75% in its cross section, contains an excessively
large amount of the eutectic phase and thereby fails to exhibit a
sufficient sacrificial effect. This also causes an insufficient
amount of a fluidized filler to form a fillet, resulting in
insufficient brazability. To avoid these, the residual filler layer
30 contains an alpha phase in an area percentage 75% or more, and
preferably in an area percentage of 85% or more in its cross
section.
[0069] The area percentage of the alpha phase may be determined by
cutting out a specimen from the aluminum alloy brazed article 10
(or an article obtained by subjecting the brazing sheet 1 to a heat
treatment at a temperature for a time identical to those in the
brazing conditions), and observing a region of the residual filler
layer 30 in the cut surface under an optical microscope at a
magnification of 25 to 100 times. Specifically, the area percentage
may be calculated by measuring the thickness of the residual filler
layer 30 and the area of the eutectic phase. Typically, an optical
micrograph may be subjected to an image analysis to measure the
area percentage of the eutectic phase or another parameter.
(Zn Content of Alpha Phase in Residual Filler Layer: 1 Percent by
Mass or More)
[0070] Zinc (Zn) is highly soluble in Al to form a solid solution.
Zinc in the filler material 3 is therefore contained also in the
alpha phase during brazing, allows the alpha phase to have a less
noble potential, and thereby allows the residual filler layer 30 to
function as a sacrificial layer. The alpha phase, which occupies
75% by area or more of the residual filler layer 30, if having a Zn
content of less than 1 percent by mass, has a not-so-less noble
potential and thereby fails to impart a sufficient sacrificial
effect to the residual filler layer 30. To avoid this, the alpha
phase in the residual filler layer 30 has a Zn content of 1 percent
by mass or more, and preferably has a Zn content of 1.5 percent by
mass or more.
[0071] Part of the aluminum alloy composition mutually migrates
between the core material 2 and the filler material 3 as a result
of hot rolling and annealing in manufacturing processes of the
brazing sheet 1, and heating in the brazing process. Accordingly,
the residual filler layer 30 may have increase or decrease in
content of the alloy composition with respect to the filler
material 3 and undergo migration of a composition from the core
material 2.
[0072] When Cu is contained in the core material 2 and/or the
filler material 3 in the brazing sheet 1, Cu is also contained in
the residual filler layer 30. In this case, the residual filler
layer 30 preferably has a Cu content of 0.4 percent by mass or
less. When Cu is contained in the core material 2 even without
being added to the filler material 3, Cu is also contained in the
filler material 3 upon the brazing process, because Cu migrates
from the core material 2 into the filler material 3 as a result of
the manufacturing processes of the brazing sheet 1 and heating in
the brazing process. In contrast, Cu contained in the filler
material 3 is distributed in a relatively larger amount in the
fluidized filler during the brazing process but is distributed in a
relatively smaller concentration in the residual filler layer 30.
However, Cu, if contained in a content of more than 0.4 percent by
mass in the residual filler layer 30, may cause the residual filler
layer 30 to have a more noble potential to thereby exhibit an
insufficient sacrificial effect. Accordingly, the residual filler
layer 30, by having a Cu content of 0.4 percent by mass or less,
may provide a larger potential difference with respect to the core
material 2 without impeding the action of Zn to provide a less
noble potential, may thereby exhibit a further satisfactory
sacrificial effect, and may allow the aluminum alloy brazed article
10 to have further better corrosion resistance.
[0073] The contents of Zn and other elements in the residual filler
layer 30 may be measured typically with an X-ray microanalyzer
(electron probe X-ray microanalyzer; EPMA). Specifically, the
concentration of a specific composition may be calculated by
detecting the intensity of each element such as Al in the residual
filler layer 30 on a cross section of a test specimen cut out from
the aluminum alloy brazed article 10.
[0074] As is described above, an aluminum alloy brazed article 10
is obtained by cladding a core material 2 with a filler material 3
to give a brazing sheet 1, and brazing the brazing sheet 1 at a
brazing temperature, in which the core material 2 is composed of an
aluminum alloy having the predetermined pitting potential, the
filler material 3 is composed of an Al--Si--Zn alloy having a Zn
content of 1 to 10 percent by mass and having a liquid fraction X
of 0.3 or more and 0.88 or less (0.3.ltoreq.X.ltoreq.0.88) at the
brazing temperature, the clad ratio (%) of the filler material 3 is
more than 15 but 30 or less (15<d.ltoreq.30), and the product
(X.times.d) of the clad ratio d and the liquid fraction X is 6 or
more and 23 or less (6.ltoreq.(X.times.d).ltoreq.23). The aluminum
alloy brazed article 10 includes the core material 2 having a more
noble potential and, provided thereon, the residual filler layer 30
containing Zn in a suitable concentration and having a sufficient
thickness, in which there is imparted a sufficient potential
difference between the residual filler layer 30 and the core
material 2. The sufficient potential difference as above allows the
aluminum alloy brazed article 10 to have good corrosion resistance.
In addition, the residual filler layer 30 has a smaller difference
in Zn content from the fluidized filler upon brazing and thereby
has a substantially equal potential to that of the fluidized
filler. This prevents the preferential corrosion of the fillet and
thereby allows the joint to have satisfactory corrosion
resistance.
[0075] In the manufacturing of the brazing sheet 1, the chemical
composition of the aluminum alloy for the formation of the core
material 2 is determined from the points of strength and corrosion
resistance necessary for the aluminum alloy brazed article 10 (heat
exchanger). In addition, the contents of elements such as Si and Zn
to be contained in the Al--Si--Zn alloy for the formation of the
filler material 3 are determined so that the filler material 3 has
a predetermined liquid fraction at the brazing temperature. These
parameters are determined typically by advance testing.
[Manufacturing Method of Aluminum Alloy Brazing Sheet for Heat
Exchangers]
[0076] An aluminum alloy brazing sheet according to an embodiment
of the present invention may be manufactured by a known method for
manufacturing a clad material. An exemplary method for
manufacturing a brazing sheet 1 according to the embodiment will be
illustrated below.
[0077] Initially, aluminum alloys having compositions for a core
material 2 and for a filler material 3 of the brazing sheet 1
according to the embodiment of the present invention are melted and
cast through continuous casting and thereby yield an ingot for the
core material, and an ingot for the filler material. The respective
ingots are faced according to necessity and subjected to a
homogenization heat treatment. The ingot for the filler material is
hot-rolled or cut so as to have a thickness corresponding to a
desired clad ratio and thereby yields a thick plate for the filler
material.
[0078] The thick plate for the filler material is layered on one
side of the ingot for the core material, is heated to 400.degree.
C. or higher, and the two members are compressed and bonded through
hot rolling (clad rolling) and thereby yield an integral sheet. The
sheet is then subjected to rough annealing according to necessity,
to cold rolling, and, where necessary with the interposition of
process annealing, to repeated cold rolling operations to a desired
gauge, and thereby yields the brazing sheet 1. The process
annealing is preferably performed at a temperature of from
350.degree. C. to 450.degree. C. for 3 hours or longer, or may be
omitted. The final cold rolling to give a desired gauge is
preferably performed to a reduction ratio of from 30% to 60%. The
work may further be subjected to finish annealing after the final
cold rolling. The finish annealing allows the material to be
softened and to exhibit more satisfactory elongation and thereby
allows the brazing sheet 1 to have better processability.
[0079] The present invention will be illustrated in further detail
with reference to several working examples below, which demonstrate
advantageous effects of the present invention, in comparison with
comparative examples which do not satisfy the conditions as
specified in the present invention.
Experimental Example 1
Preparation of Brazing Sheet
[0080] Ingots for the core material were prepared from aluminum
alloys (C1 to C19) for the core material according to the known
procedure and subjected to a homogenization heat treatment at
500.degree. C. for 8 hours. The aluminum alloys had chemical
compositions given in Table 1. The pitting potentials of the
aluminum alloys C1 to C19 with reference to a silver-silver
chloride electrode (vs. Ag/AgCl) are also indicated in Table 1.
Likewise, ingots for the filler material were prepared from
aluminum alloys (Al--Si--Zn alloys) for the filler material
according to a known procedure, subjected to a homogenization heat
treatment, cut to predetermined thicknesses corresponding to clad
ratios of respective specimens, and thereby yielded thick plates
for the filler material. The aluminum alloys herein had chemical
compositions given in Tables 2, 3, and 4. The liquid fractions of
the aluminum alloys for the filler material at 600.degree. C. are
also shown in Tables 2, 3, and 4, whereas the brazing temperature
in the after-mentioned brazing process was set to 600.degree.
C.
[0081] In combinations for the respective specimens given in Tables
2, 3, and 4, each thick plate for the filler material was layered
on each ingot for the core material, the laminate was heated to
450.degree. C., compressed and bonded through hot rolling, and
thereby yielded a series of plates. Without rough annealing, the
plates were subsequently subjected to cold rolling, to process
annealing at 400.degree. C. for 5 hours, further to cold rolling to
a reduction ratio of 50% to have final gauges as mentioned below,
finally to finish annealing at 300.degree. C. for 3 hours, and
thereby yielded specimens (No. 1 to 47, 51 to 63, and 71 to 80) as
aluminum alloy brazing sheets for heat exchangers. Regarding the
gauges of brazing sheets, Specimens Nos. 1 to 47 (Table 2) each had
a gauge of 1.0 mm, Specimens Nos. 51 to 63 (Table 3) each had a
gauge of 0.35 mm, and Specimens Nos. 71 to 80 (Table 4) each had a
gauge of 0.20 mm.
TABLE-US-00001 TABLE 1 Pitting Core potential material Chemical
composition of core material VS alloy aluminum alloy (mass %)
(Ag/AgCl) type Cu Si Mn Ti Mg Al * ( mV ) C1 0.1 0.9 1.65 0.15 0.05
Remainder -643 C2 0.3 0.9 1.65 0.15 0.05 Remainder -628 C3 0.5 0.9
1.65 0.15 0.05 Remainder -613 C4 0.85 0.9 1.65 0.15 0.05 Remainder
-595 C5 1.2 0.9 1.65 0.15 0.05 Remainder -564 C6 1.6 0.9 1.65 0.15
0.05 Remainder -545 C7 0.85 0.5 1.65 0.15 0.05 Remainder -592 C8
0.85 1.5 1.65 0.15 0.05 Remainder -588 C9 0.85 1.7 1.65 0.15 0.05
Remainder -580 C10 0.85 0.9 0.3 0.15 0.05 Remainder -598 C11 0.85
0.9 0.8 0.15 0.05 Remainder -595 C12 0.85 0.9 1.9 0.15 0.05
Remainder -583 C13 0.85 0.9 1.65 0.04 0.05 Remainder -600 C14 0.85
0.9 1.65 0.3 0.05 Remainder -585 C15 0.85 0.9 1.65 0.5 0.05
Remainder -580 C16 0.85 0.9 1.65 0.15 0.25 Remainder -602 C17 0.85
0.9 1.65 0.15 0.45 Remainder -609 C18 0.85 0.9 1.65 0.15 0.55
Remainder -618 C19 0.15 0.5 0.3 0.05 0.05 Remainder -686 *
Including inevitable impurities Underlined data are out of scope of
the present invention
[Preparation of Aluminum Alloy Brazed Article]
[0082] (Brazing Process Method)
[0083] A commercially available noncorrosive flux was applied to
the surface of the filler material of each of the above-prepared
brazing sheets in a mass of coating of 4 g/m.sup.2, the work was
then hung from a jig, followed by a brazing process by holding the
same in a nitrogen atmosphere having an oxygen concentration of 200
ppm or less at a brazing temperature of 600.degree. C. for 2
minutes, and thereby yielded a series of aluminum alloy brazed
articles (brazed, heat-treated articles). Independently, the
brazing sheets were assembled according to the details of the
following test, subjected to a brazing process, and thereby yielded
another series of aluminum alloy brazed articles.
[0084] (Preparation of Aluminum Alloy Brazed Article for Gap
Filling Test)
[0085] Each of the brazing sheets of Specimens Nos. 1 to 47 (gauge:
1.0 mm) in Table 2 was cut out to give a test specimen having a
width of 20 mm and a length of 60 mm. A flux was applied to the
surface of the filler material side of the test specimen, and the
resulting test specimen was placed horizontally so that the applied
surface faced upward to give a lower plate. With reference to FIG.
2(a), a 3003 alloy plate 1 mm thick, 25 mm wide, and 55 mm long as
an upper plate was fixed vertically on the test specimen (lower
plate) with the interposition of a spacer, i.e., a round rod 2 mm
in diameter. The spacer herein was positioned at a distance of 50
mm from one end (point of contact with the lower plate) of the
upper plate (see FIG. 2(b)). This was subjected to brazing under
the brazing conditions.
[0086] (Preparation of Aluminum Alloy Brazed Article for Shaped
Portion Joint Test)
[0087] Each of the brazing sheets of Specimens Nos. 51 to 63
(gauge: 0.35 mm) in Table 3 and of Specimens Nos. 71 to 80 (gauge:
0.20 mm) in Table 4 was pressed and shaped into a corrugated sheet
illustrated in FIG. 3(a). Specifically, the corrugated sheet had a
repetition pitch L of ridges and grooves of 8 mm (ridges and
grooves each having a length of 4 mm) and a difference in height H
between the top face and bottom face of the ridges and grooves of 3
mm. Two corrugated sheets were prepared for each specimen, were
laid plane-symmetrically so that the filler material sides of the
two sheets faced each other, and subjected to brazing under the
brazing conditions.
[Measurement and Evaluation]
[0088] (Thickness of Residual Filler Layer and Area Percentage of
Alpha Phase)
[0089] A measurement specimen was cut out from each of the brazed,
heat-treated articles, and the cross section thereof was observed
at arbitrary five view fields under an optical microscope. The
thicknesses of the residual filler layers in the five view fields
were respectively measured and averaged, and the average of the
measured data in the five view fields was expressed as percentage
with respect to the gauge (1.0 mm, 0.35 mm, or 0.20 mm) of the
sample brazing sheet. Independently, optical microscopic images in
arbitrary five view fields were analyzed using a commercially
available image analysis software to measure the area percentage of
eutectic phases. The area percentages of eutectic phases in the
five view fields were averaged, and the average was subtracted from
100(%) to give an area percentage of alpha phase. The measured
thicknesses of the residual filler layer, and the area percentages
of alpha phase are indicated in Tables 2, 3, and 4.
[0090] (Zn Content of Alpha Phase in Residual Filler Layer)
[0091] An alpha phase observed in the cross section of the
measurement specimen obtained from each of the brazed, heat-treated
articles was subjected to a line analysis by EPMA to detect
intensities of aluminum alloy elements, and a Zn content was
calculated at a point where the Zn concentration reaches maximum.
The determined Zn contents are indicated in Tables 2, 3, and 4.
[0092] (Evaluation of Brazability)
[0093] The fillet sizes of the prepared aluminum alloy brazed
articles were measured. Specifically, the lengths of fillets formed
in the aluminum alloy brazed articles for gap filling testing
obtained from Specimens Nos. 1 to 47 (gauge: 1.0 mm) in Table 2 was
measured as illustrated in FIG. 2(b). The results are shown in
Table 2. For Specimens Nos. 1 to 47, samples having a fillet length
of 20 mm or more were evaluated as accepted.
[0094] Independently, the heights of fillets formed in the aluminum
alloy brazed articles for shaped portion joint testing obtained
from Specimens Nos. 51 to 63 (gauge: 0.35 mm) in Table 3 and
Specimens Nos. 71 to 80 (gauge: 0.20 mm) in Table 4 were measured
as illustrated in FIG. 3(b). The results are indicated in Tables 3
and 4. For Specimens Nos. 51 to 63, samples having a fillet height
of 200 .mu.m or more were evaluated as accepted. For Specimens Nos.
71 to 80, samples having a fillet height of 150 .mu.m or more were
evaluated as accepted.
[0095] (Evaluation of Corrosion Resistance at Joint)
[0096] After the measurement of fillet size for the evaluation of
brazability on the aluminum alloy brazed articles (see FIG. 2 and
FIG. 3), the surface of a portion of each specimen other than the
filler material (residual filler layer) surface and the fillet,
which portion was to be in contact with a corrosive environment
actually, was sealed with a sealing tape and a paint. The resulting
aluminum alloy brazed article was subjected to a copper-accelerated
acetic acid salt spray test (CASS test; JIS Z 2371) for 1000 hours
as a corrosion test. After the corrosion test, the length or height
of the fillet was measured, and a residual ratio with respect to
the length or height of the fillet measured for the evaluation of
the brazability before the corrosion test was calculated. The
determined fillet residual ratios are shown in Tables 2, 3, and 4.
Samples having a fillet residual ratio of 70% or more were
evaluated as accepted.
[0097] (Evaluation of Corrosion Resistance at Flat Portion)
[0098] A specimen 60 mm long and 50 mm wide was cut out from each
of the brazed, heat-treated articles, and the surface of the core
material side and end surface of the specimen were sealed with a
sealing tape, whereas the filler material (residual filler layer)
surface was defined as a test surface. The resulting specimen was
subjected to a CASS test (JIS Z 2371) for 1000 hours as a corrosion
test. After the corrosion test, the cross section of the specimen
was observed under an optical microscope, and a corrosion depth was
measured. The maximum corrosion depth in the observed cross section
was indicated on a percentage basis per the gauge (1.0 mm, 0.35 mm,
or 0.20 mm) of the sample brazing sheet, and the results are shown
in Tables 2, 3, and 4. Samples having a maximum corrosion depth of
50% or less of the gauge of the brazing sheet before brazing were
evaluated as accepted.
TABLE-US-00002 TABLE 2 Corrosion resistance Flat portion Aluminum
alloy brazing sheet (gauge 1.0 mm) Residual filler layer Maxi-
Filler material in brazed article mum Joint Core Aluminum Alpha
phase corro- Fillet Braza- mate- alloy Liquid (Liquid Thick- Zn
sion resid- bility Specimen rial composition * fraction Clad Thick-
fraction) .times. [Zn] .times. ness Area content depth ual Fillet
Cate- Alloy (mass %) (600.degree. ratio ness (Clad (Thick- (% to
ratio (mass (% to ratio length gory No. type Si Mn Zn C.) ( % ) (
.mu.m ) ratio) ness) gauge) (%) %) gauge) ( % ) ( mm ) Exam- 1 C3 5
0.02 2 0.51 20 200 10.2 400 18.2 93.1 1.8 25 87 22 ple 2 C3 7 0.02
2 0.76 20 200 15.2 400 14.1 94.8 1.8 24 95 33 3 C3 7 0.04 2 0.76 20
200 15.2 400 15.4 83.3 1.7 22 82 31 4 C3 7 0.06 2 0.76 20 200 15.2
400 18.7 76.0 1.6 28 74 23 5 C3 6 0.02 3 0.67 20 200 13.4 600 14.5
94.7 2.5 26 85 34 6 C4 6 0.02 3 0.67 20 200 13.4 600 14.4 94.8 2.3
22 86 33 7 C16 6 0.02 3 0.67 20 200 13.4 600 18.1 94.3 2.3 23 84 29
8 C3 7 0.02 4 0.83 20 200 16.6 800 11.5 97.2 3.6 22 89 34 9 C3 3
0.02 9 0.44 20 200 8.8 1800 18.4 89.9 8.4 23 79 25 10 C1 7 0.02 2
0.76 20 200 15.2 400 14.2 95.0 1.6 32 84 33 11 C2 7 0.02 2 0.76 20
200 15.2 400 14.1 93.9 1.7 29 91 35 12 C4 7 0.02 2 0.76 20 200 15.2
400 14.1 94.4 1.8 25 93 34 13 C5 7 0.02 2 0.76 20 200 15.2 400 13.8
95.1 1.6 28 98 32 14 C6 7 0.02 2 0.76 20 200 15.2 400 13.9 95.1 1.8
49 97 32 15 C7 7 0.02 2 0.76 20 200 15.2 400 13.9 95.2 1.6 25 95 34
16 C8 7 0.02 2 0.76 20 200 15.2 400 14.2 94.3 1.7 24 94 32 17 C9 7
0.02 2 0.76 20 200 15.2 400 14.2 94.9 1.8 43 93 33 18 C10 7 0.02 2
0.76 20 200 15.2 400 14.1 94.7 1.6 26 93 34 19 C11 7 0.02 2 0.76 20
200 15.2 400 14.2 94.6 1.8 27 93 32 20 C12 7 0.02 2 0.76 20 200
15.2 400 13.7 93.4 1.7 39 97 33 21 C13 7 0.02 2 0.76 20 200 15.2
400 14.3 94.9 1.8 29 92 33 22 C14 7 0.02 2 0.76 20 200 15.2 400
14.1 95.2 1.7 22 94 34 23 C15 7 0.02 2 0.76 20 200 15.2 400 14.0
94.1 1.7 27 94 34 24 C16 7 0.02 2 0.76 20 200 15.2 400 18.2 94.2
1.7 23 89 29 25 C17 7 0.02 2 0.76 20 200 15.2 400 18.5 79.2 1.6 25
87 25 26 C18 7 0.02 2 0.76 20 200 15.2 400 18.9 76.3 1.8 23 79 22
27 C6 5 0.02 2 0.51 20 200 10.2 400 17.9 92.5 1.8 38 91 23 28 C9 5
0.02 2 0.51 20 200 10.2 400 18.1 93.8 1.8 28 88 25 29 C4 3.5 0.02 2
0.34 20 200 6.8 400 19.1 81.0 1.8 24 92 21 30 C4 8 0.02 2 0.88 25
250 22.0 500 17.2 98.2 1.6 26 93 33 Com- 31 C3 1.5 0.02 2 0.07 20
200 1.4 400 19.5 98.3 1.7 29 85 18 par- 32 C3 10 0.02 2 1 20 200
20.0 400 3.6 98.2 0.9 58 55 36 ative 33 C3 7 0.02 8 1 20 200 20.0
1600 4.8 97.2 3.9 65 15 35 Exam- 34 C3 5 0.02 11 0.82 20 200 16.4
2200 12.3 97.1 8.7 23 13 35 ple 35 C3 2 0.02 9 0.28 20 200 5.6 1800
18.9 73.2 4.3 31 13 18 36 C3 9 0.02 1 0.97 20 200 19.4 200 3.9 98.0
0.5 57 65 34 37 C19 7 0.02 2 0.76 20 200 15.2 400 14.5 95.0 1.7 63
81 34 38 C3 2.5 0.2 3 0.23 20 200 4.6 600 18.9 71.4 2.6 29 95 19 39
C3 3 0.1 2 0 27 20 200 5.4 400 19.2 69.9 2.6 26 93 17 40 C3 7 0.02
6 0.90 20 200 18.0 1200 3.7 98.4 3.2 23 31 36 41 C3 6 0.02 9 0.89
20 200 17.8 1800 4.2 98.3 4.1 24 27 34 42 C3 3.5 0.02 2 0.34 15 150
5.1 300 13.9 79.2 1.8 23 87 15 43 C3 8 0.02 2 0.88 30 300 26.4 600
20.5 96.1 1.7 51 73 36 44 C3 7.5 0.02 0.5 0.80 20 200 16.0 100 14.3
97.5 0.43 59 88 33 45 C3 8 0.02 2 0.88 13 130 11.4 260 11.2 80.9
1.7 27 91 17 46 C3 8 0.02 2 0.88 35 350 30.8 700 21.3 87.3 1.6 55
94 38 47 C3 3.5 0.02 2 0.34 35 350 11.9 700 31.9 70.9 1.7 32 93 14
Underlined data are out of the scope of the present invention * The
remainder being Al and inevitable impurities Boldfaced data are
rejected
TABLE-US-00003 TABLE 3 Corrosion resistance Flat portion Maxi-
Aluminum alloy brazing sheet (gauge 0.35 mm) Residual filler layer
mum Joint Filler material in brazed article corro- Fillet Braza-
Core Aluminum alloy Liquid (Liquid Thick- Alpha phase sion resid-
bility material composition * fraction Clad Thick- fraction)
.times. [Zn] .times. ness Area Zn depth ual Fillet Specimen Alloy
(mass %) (600.degree. ratio ness (Clad (Thick- (% to ratio content
(% to ratio length Category No. type Si Mn Zn C.) ( % ) ( .mu.m )
ratio) ness) gauge) (%) (mass %) gauge) ( % ) ( .mu.m ) Example 51
C3 6 0.02 3 0.67 17 60 11.5 180 12.5 93.2 1.6 27 93 420 52 C4 6
0.02 3 0.67 17 60 11.5 180 13.1 94.7 1.7 28 95 460 53 C16 6 0.02 3
0.67 17 60 11.5 180 12.5 87.3 1.5 25 89 390 54 C3 6 0.02 3 0.67 23
80 15.3 240 16.6 94.1 1.8 24 97 710 55 C4 6 0.02 3 0.67 23 80 15.3
240 15.9 95.3 1.7 24 96 715 56 C16 6 0.02 3 0.67 23 80 15.3 240
16.4 94.3 1.7 22 95 650 57 C3 4 0.02 5 0.50 17 60 8.6 300 15.3 88.6
2.4 22 79 320 58 C3 6 0.02 5 0.78 17 60 13.4 300 10.3 95.1 2.2 21
76 590 Compar- 59 C3 3.5 0.02 3 0.35 16 56 5.6 168 14.7 78.6 1.8 26
89 190 ative 60 C3 1.5 0.02 2 0.07 17 60 1.2 120 16.5 98.3 1.7 24
72 54 Example 61 C3 6 0.02 9 0.89 17 60 15.3 540 3.5 95.3 4.6 52 78
760 62 C3 7 0.02 2 0.76 14 50 10.9 100 11.9 96.2 0.9 64 96 490 63
C3 7.5 0.02 0.5 0.80 17 60 13.7 30 10.6 96.2 0.36 55 80 610 * The
remainder being Al and inevitable impurities Underlined data are
out of the scope of the present invention Boldfaced data are
rejected
TABLE-US-00004 TABLE 4 Corrosion resistance Flat portion Maxi-
Aluminum alloy brazing sheet (gauge 0.20 mm) Residual filler layer
mum Joint Filler material in brazed article corro- Fillet Braza-
Core Aluminum alloy Liquid (Liquid Thick- Alpha phase sion resid-
bility material composition * fraction Clad Thick- fraction)
.times. [Zn] .times. ness Area Zn depth ual Fillet Specimen Alloy
(mass %) (600.degree. ratio ness (Clad (Thick- (% to ratio content
(% to ratio length Category No. type Si Mn Zn C.) ( % ) ( .mu.m )
ratio) ness) gauge) (%) (mass %) gauge) ( % ) ( .mu.m ) Example 71
C3 4 0.02 5 0.50 18 35 8.8 175 16.1 88.6 2.3 37.5 79 450 72 C3 6
0.02 5 0.78 18 35 13.7 175 12.9 92.3 2.2 40 81 580 73 C16 6 0.02 5
0.78 18 35 13.7 175 12.5 94.6 2.3 36 72 575 74 C3 7 0.02 4 0.83 18
35 14.5 140 7.9 98.3 2.1 42.5 85 590 75 C3 6 0.02 3 0.67 18 35 11.7
105 13.7 94.0 1.4 45 91 520 76 C16 7 0.02 4 0.83 18 35 14.5 140 8.3
97.5 2.2 43.5 85 585 Compar- 77 C3 2.5 0.2 3 0.23 18 35 4.0 105
17.8 70.2 1.5 32.5 74 130 ative 78 C3 10 0.02 2 1 18 35 17.5 70 3.1
97.5 0.9 58 23 700 Example 79 C3 3.5 0.02 3 0.35 15 30 5.3 90 14.2
77.5 1.6 41.5 86 145 80 C3 7 0.02 4 0.80 30 60 24.0 240 22.3 97.6
2.0 63 73 740 * The remainder being Al and inevitable impurities
Underlined data are out of the scope of the present invention
Boldfaced data are rejected
[0099] Tables 2, 3, and 4 demonstrate as follows. Specimens Nos. 1
to 30, 51 to 58, and 71 to 76 each satisfied conditions for
aluminum alloy brazing sheets for heat exchangers according to the
present invention on the pitting potential of the aluminum alloy
constituting the core material (see Table 1), the Zn content and
the liquid fraction at the brazing temperature (600.degree. C.) of
the Al--Si--Zn alloy constituting the filler material, and the clad
ratio of the filler material and a product thereof with the liquid
fraction. These specimens were brazed and thereby yielded aluminum
alloy brazed articles according to the present invention, which
brazed articles each include a core material, and formed thereon, a
residual filler layer having a sufficient thickness and including
an alpha phase with a suitable Zn concentration. The brazed
articles were satisfactory in all the corrosion resistance of the
joint, the corrosion resistance of the flat portion, and the
brazability. In contrast, Specimens Nos. 31 to 47, 59 to 63, and 77
to 80 did not satisfy one or more of the conditions for aluminum
alloy brazing sheets for heat exchangers according to the present
invention and thereby gave aluminum alloy brazed articles which
were unsatisfactory in brazability and/or corrosion resistance.
[0100] (Evaluation by Chemical Composition of Core Material)
[0101] Specimen No. 37 had insufficient Cu and Mn contents in the
core material (C19), thereby had a pitting potential less noble
than the range specified in the present invention, and exhibited an
insufficient potential difference with respect to the residual
filler layer, resulting in an insufficient sacrificial effect of
the residual filler layer. The specimen thereby exhibited poor
corrosion resistance in the flat portion.
[0102] (Evaluation by Chemical Composition and Clad Ratio of Filler
Material)
[0103] Specimens Nos. 31, 35, 38, 39, 60, and 77 each had an
insufficient liquid fraction of the filler material, thereby failed
to ensure a sufficient fluidized filler during brazing, and
indicated poor brazability. Specimen No. 35 had a Zn content of the
filler material near to the upper limit, thereby gave a small
fillet with a high Zn concentration, and indicated poor corrosion
resistance at the joint. In contrast, Specimens Nos. 32, 33, 36,
40, 41, 61, and 78 each had an excessively high liquid fraction of
the filler material, thereby gave a brazing metal which excessively
fluidized during brazing to give a residual filler layer having an
insufficient thickness, and indicated poor corrosion resistance of
at least one of the flat portion and the joint.
[0104] Specimen No. 34 had an excessively high Zn content of the
filler material and thereby gave a fluidized filler with a higher
Zn concentration, namely gave a fillet with a higher Zn
concentration, resulting in poor corrosion resistance at the joint.
In contrast, Specimens Nos. 44 and 63 each had an insufficient Zn
content of the filler material, thereby gave, after brazing, a
residual filler layer having an insufficient Zn concentration and
exhibiting insufficient sacrificial effect, resulting in poor
corrosion resistance in the flat portion.
[0105] Specimens Nos. 42, 45, and 79 each had an insufficient clad
ratio of the filler material and thereby exhibited poor
brazability. Specimen No. 62 exhibited certain brazability, because
the filler material had a relatively high liquid fraction in spite
of having an insufficient clad ratio. However, this specimen had
poor corrosion resistance in the flat portion, because the filler
material had an excessively small thickness and a low Zn content in
the vicinity of the lower limit, and gave a residual filler layer
with an insufficient Zn concentration. In contrast, Specimen No. 47
exhibited poor brazability, because the filler material had an
excessively high clad ratio and a low liquid fraction in the
vicinity of the lower limit, thereby gave a larger amount of a
brazing metal not contributing to fluidization, and this remained
as a residual filler layer on the core material. Specimen No. 46
exhibited a large corrosion depth (was largely corroded) in the
flat portion, because the filler material had an excessively high
clad ratio, had a high liquid fraction near to the upper limit with
an excessively high product between them, thereby gave an
excessively large amount of fluidized filler, which eroded the core
material. Likewise, Specimens Nos. 43 and 80 exhibited poor
corrosion resistance in the flat portion, because the filler
material had an excessively large product between the liquid
fraction and the clad ratio, although these parameters are each
within the range specified in the present invention and thereby
gave an excessively large amount of fluidized filler which eroded
the core material. In contrast, Specimen No. 59 indicated poor
brazability, because the filler material had an insufficient
product between the liquid fraction and the clad ratio, although
these parameters are within the ranges specified in the present
invention, and the specimen thereby gave an insufficient amount of
fluidized filler.
Experimental Example 2
[0106] Next, another experimental example was performed to verify
the advantageous effects of the present invention, in which
aluminum alloys for the filler material further added with Cu in
different contents were used.
[Preparation of Aluminum Alloy Brazing Sheet]
[0107] Brazing sheets (gauge: 1.0 mm) of Specimens Nos. 81 to 89 in
Table 5 and brazing sheets (gauge: 0.35 mm) of Specimens Nos. 91 to
99 in Table 6 were prepared by the procedure of Experimental
Example 1, using aluminum alloys (C3 and C4) having the chemical
compositions given in Table 1, and aluminum alloys (Al--Si--Zn
alloys) for the filler material having chemical compositions given
in Tables 5 and 6. The obtained brazing sheets were subjected to a
brazing process by holding at a brazing temperature of 600.degree.
C. for 2 minutes by the procedure of Experimental Example 1 and
thereby yielded brazed, heat-treated articles. In addition,
aluminum alloy brazed articles illustrated in FIG. 2 were prepared
from Specimens Nos. 81 to 89, and aluminum alloy brazed articles
illustrated in FIG. 3 were prepared from Specimens Nos. 91 to
99.
[Measurement and Evaluation]
[0108] On the above-prepared brazed, heat-treated articles, the
thickness of the residual filler layer, and the area percentage and
Zn content of the alpha phase were measured, and the corrosion
resistance in the flat portion was evaluated by performing a
corrosion test, respectively by the procedures of Experimental
Example 1. Independently, on the aluminum alloy brazed articles,
the brazability was evaluated and the corrosion resistance at the
joint was evaluated by performing a corrosion test. The results are
indicated in Tables 5 and 6.
TABLE-US-00005 TABLE 5 Corrosion resistance Flat portion Maxi-
Aluminum alloy brazing sheet (gauge 1.0 mm) Residual filler layer
mum Joint Core Filler material in brazed article corro- Fillet
Braza- mate- Aluminum alloy Liquid (Liquid Thick- Alpha phase sion
resid- bility rial composition * fraction Clad Thick- fraction)
.times. [Zn] .times. ness Area Zn depth ual Fillet Specimen Alloy
(mass %) (600.degree. ratio ness (Clad (Thick- (% to ratio content
(% to ratio length Category No. type Si Mn Zn Cu C.) ( % ) ( .mu.m
) ratio) ness) gauge) (%) (mass %) gauge) ( % ) ( .mu.m ) Example
81 C3 6.8 0.02 2 0.05 0.76 20 200 15.2 400 14.2 94.3 1.8 27 96 33
82 C3 6.7 0.02 2 0.1 0.76 20 200 15.2 400 14.3 94.7 1.8 28 97 34 83
C3 6.7 0.02 2 0.2 0.76 20 200 15.2 400 14.1 94.2 1.8 28 98 32 84 C3
6.6 0.02 2 0.4 0.76 20 200 15.2 400 14.2 94.2 1.9 35 99 34 85 C4
6.8 0.02 2 0.05 0.76 20 200 15.2 400 14.4 94.1 1.8 26 96 35 86 C4
6.7 0.02 2 0.2 0.76 20 200 15.2 400 14.1 94.1 1.7 27 97 31 87 C4
6.6 0.02 2 0.4 0.76 20 200 15.2 400 14.1 94.2 1.7 37 99 34 Compar-
88 C3 6.4 0.02 2 0.8 0.76 20 200 15.2 400 14.2 94.1 1.8 54 98 34
ative 89 C4 6.4 0.02 2 0.8 0.76 20 200 15.2 400 14.3 94.1 1.8 52
100 33 Example * The remainder being Al and inevitable impurities
Underlined data are out of the scope of the present invention
Boldfaced data are rejected
TABLE-US-00006 TABLE 6 Corrosion resistance Flat portion Maxi-
Aluminum alloy brazing sheet (gauge 0.35 mm) Residual filler layer
mum Joint Core Filler material in brazed article corro- Fillet
Braza- mate- Aluminum alloy Liquid (Liquid Thick- Alpha phase sion
resid- bility rial composition * fraction Clad Thick- fraction)
.times. [Zn] .times. ness Area Zn depth ual Fillet Specimen Alloy
(mass %) (600.degree. ratio ness (Clad (Thick- (% to ratio content
(% to ratio length Category No. type Si Mn Zn Cu C.) ( % ) ( .mu.m
) ratio) ness) gauge) (%) (mass %) gauge) ( % ) ( .mu.m ) Example
91 C3 5.8 0.02 3 0.05 0.67 23 80 15.3 240 16.5 94.3 1.8 25 97 712
92 C3 5.8 0.02 3 0.1 0.67 23 80 15.3 240 16.5 94.3 1.8 27 98 715 93
C3 5.7 0.02 3 0.2 0.67 23 80 15.3 240 16.7 94.1 1.8 30 99 710 94 C3
5.6 0.02 3 0.4 0.67 23 80 15.3 240 16.2 93.8 1.7 36 100 710 95 C4
5.8 0.02 3 0.05 0.67 23 80 15.3 240 16.6 94.8 1.7 24 97 720 96 C4
5.7 0.02 3 0.2 0.67 23 80 15.3 240 16.8 94.7 1.8 28 99 710 97 C4
5.6 0.02 3 0.4 0.67 23 80 15.3 240 15.9 94.5 1.7 36 100 715 Compar-
98 C3 5.4 0.02 3 0.8 0.66 23 80 15.1 240 16.1 94.5 1.7 57 100 715
ative 99 C4 5.4 0.02 3 0.8 0.66 23 80 15.1 240 16.3 93.9 1.8 53 100
720 Example * The remainder being Al and inevitable impurities
Underlined data are out of the scope of the present invention
Boldfaced data are rejected
[0109] (Evaluation by Chemical Composition of Filler Material)
[0110] Specimens Nos. 81 to 84 and 88, and Specimens Nos. 85 to 87
and 89 in Table 5 are examples and comparative examples
corresponding to Specimen No. 2 and Specimen No. 12, respectively,
in Table 2 of Experimental Example 1, except for further containing
Cu in increasing amounts in this order in the aluminum alloy for
constituting the filler material. Likewise, Specimens Nos. 91 to 94
and 98, and Specimens Nos. 95 to 97 and 99 in Table 6 are examples
and comparative examples corresponding to Specimen No. 54 and
Specimen No. 55, respectively, in Table 3, except for further
containing Cu in increasing amounts in this order in the aluminum
alloy for constituting the filler material. Tables 5 and 6
demonstrate that, with an increasing Cu content of the filler
material, the residual filler layer after brazing tended to have a
decreasing sacrificial effect but the fillet tended to have an
increasing corrosion resistance. If the Cu content increased over
the range specified in the present invention as in Specimens Nos.
88, 89, 98, and 99, the corrosion resistance of the flat portion
was as poor as in Specimens Nos. 44 and 63 (see Tables 2 and 3)
having an insufficient Zn content of the filler material,
indicating that the residual filler layer lost its sacrificial
effect due to Zn addition.
[0111] While the present invention has been described in detail
with reference to the specific embodiments and working examples
thereof, it is to be understood that the invention be not limited
by any of the details of description, but rather be construed
broadly within its spirit and scope as set out in the appended
claims. In addition, it is obvious that various changes,
modifications, or equivalent arrangements may be made therein
without departing from the spirit and scope of the invention.
* * * * *