Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF _IE INV~:NTION
Fielcl of the Invention
.
~ he present invention relates to a brazed aluminum
heat exchanger having an improved corrosion resistance.
Description of the Prior Art
__ .__ _ _ _
A1 alloys have been well known as materials having good
corrosion resis~ance. However, when they are used for a brazed
structure such as a heat exchanger, the brazing material acts on
the aluminum base material ca-thodically, whereby -the corrosion
of the aluminum base material is electrochemically facilitated.
Further, Si in the brazing material is likely to intergranularly
diffuse into the aluminum base material, whereby intergranular
corrosion tends to form in -the aluminum base material with Si as
nuclei. Furthermore, the corrosion resistance ofthe base material
tends to be degraded by the high temperature heating at the time
of brazing, and the corrosion resistance becomes inadequa-te under
a moisture condition as in the inner sur~ace of a radiator tube
or tank even when there is no corrosion facilitating effect of the
brazing material. Accordingly, it has been desired to improve the
corrosion resistance.
The following methods have been proposed to prevent
development of such corrosion:
(13 a method in which a certian element such as Zn~ Sn~ or
In is added to a bracing material thereby to modify the brazing
material to have an anodic ~unction;
(2~ a method in which the above mentioned element having an
anodic function is added to the fin or corrosion preventive clad
layer of the heat exchanger thereby protecting other main com-
ponents having a function as a heat exchanger wall from corrosion
by means of the anode function;
1 ~3~ a method in which the Al base material is irnproved and
reinforced against the in-tergranular diffusion of Si; and
~ 4) a method in which a third element is added to the Al
base material to modify the base rnaterial to have a cathodic
function rela-tive to the brazing material~
When Zn is used as the elemen-t having an anodic func-
tion in the above mentioned methods, it may be possible to attain
a certain improvement in the corrosion resistance, but, in a
vacuum brazing method, Zn is likely to evaporate and be freed as
it has a high vapour pressure, thus leading to problems such
that the corrosion preventive effect is thereby diminished and
the furnace is contaminated. On the other hand, in a method
wherein Sn or In i.s used instead of Zn, no adequate corrosion pre-
ventive effect is ob-tainable and the processability becomes poor,
although there will be no problem of evaporation.
Further, as the above mentioned methods (c) and (d),
there have been an attempt to add Cu, Fe, Cr or Z~ to JIS 3003
material commonly used as the brazing sheet, or to modify the
heating conditions such as soakinc; conditions. However, no sat-
isfactory results have no-t yet been obtained.
Further, the above mentioned 3003 material contains Mn
as the major component to improve the strength, and it has a good
corrosion resistance for general purposes. However, if it is sub-
jected to a high temperature heating immediately after the brazing,
the susceptibili.ty to the intergranular corrosion is greatly
increased, and it becomes likely to be damaged by corrosion within
a short period of time. Thus, an improvement in thl.s respect has
been desired,
Generally, it is common in many cases to use as a tub-
ular material for a heat exchanger a composite material clad with
r~
1 a brazing layer and a sacrificial anode layer. In an extrusionmethod as a methocl for produci.ng such a tube, the billet forminy
becomes inevitably complicated, and the production costs become
hi.gh. Accordingly, for the production of the tubes, :it is most
suitable to form them from strips and to weld them by a high
frequency resistance or high frequency induction ~elding.
SUMMA_Y OF THE INVENTION
Accordingly, it i.s an object of the present invention
to provide a brazed aluminum heat exchanger having a good corro-
sion resistance and comprising a main component made of an Alalloy havi.ng a low intergranular corrosion susceptibility after
the brazing, a yood corrosion resistance and a relatively noble
potential and a subsidiary component made of an Al alloy having
a less noble potential than the alloy of the main component.
Another object of the present i.nventi~n is to overcome
the above mentioned difficulties and problems inherent to the
conventional heat exchanger tubes and to provide a tube for the
aluminum heat exchanger, which has a good corrosion resistance
even after the vacuum brazing, and which are par-ticularly useful
2~ as a tube for a radiator for automobiles and a heater core.
Thus, the present invention provides a brazed heat
exchanger comprising a main component such as a tube, a shell or
a tubular sheet, which is fatal to the heat exchanger if damaged
by corrosion, and a subsidiary component such as a sacrificial
anode clad layer or a fin, which is not immediately fàtal to the
heat exchanger if damaged by corrosion, and it is characterized
in that the main component is made of an alloy comprising from
0,2 to 2~0Po of Cu, if necessary one or more selected from the
group consisting of from 0.01 to 0.5~ of Zr, from 0.05 to 0.5~ of
Mn and from 0.05 to 0.5% of Cr, and the rest being Al and impur-
ities, and the subsidiary component is made of an alloy selected
1 from the group consisting of: alurninum, ~I~Mn and ~l-Mg-Si alloys
containing at mos-t 0. 2~G of Cu.
Other objects and fea-tures of the present invention
will become apparent from the following descrip-~ion of the pre-
ferred embodiments.
BRIEF DESCRIPTION OF T;IE DRAWINGS
FIGURE 1 is a schematic view showing an assembly of the
brazing sheets and fins in an embodiment of the present invention.
FIGURES 2(,a) to (,d) are enlarged photographi.c views
showing bypical cross sections of the brazing shee-ts after sub-
jected to CASS Test in the Examples of the present invention.
FIGURES 3(a) to ('f) are cross sectional photographic
views showing the s-tates of corrosion of Al clad materials in
Example 2,
FIGURE 4 is a schematic view of an apparatus used for
the corrosion test~
FIGURES 5(.a) to (d) are microscopic photographs of
aluminum heat exchanger tubes accordi.ng to the present invention
and comparative tubes after they have been subjected to the
corrosion tests~ '
DETAILED DE,SCRIPTION OF THE PREF~RRED EMBODIMENTS
The above mentioned main component is a part of the
heat exchanger such as a tube~ a shell~ a tank or an end plate,
which is fatal to the heat exchanger if damaged by penetrating
corrosion. On the o-ther hand, the subsidiary component is a part
such as a fin or a corrosion preventive anode clad layer which
does not have a function as a partition wall for different: kinds
of fluids and which is not immedi.ately fatal to the heat exchanger
even when damaged by corrosion. However, the main component and
the subsidiary component are relative to each other, and accord-
ingly the combination is not restricted to the above mentioned
examples,
r~,C.;~
1 ~s mentioned above, the mai:n component of the present
invention is made of an alloy comprising from 0,2 to 2.0% of Cu
as an essential element, one or more selected from the group
consisting of from 0,01 -to 0.5% of Zr, from 0~05 to 0,5% of Mn
and from 0.05 to 0,5% of Cr as optional elements, and the rest
being ~1 and impurities, The subsidiary component is made of a
pure aluminum (.JIS lxxx~, A1-Mn (JIS 3xxx) or Al-Mg-Si (JIS 6xxx)
alloy containing at most 0,2% of Cu, The above JIS 6~xx is an
alloy of a JIS number in the order of 6000, such as JIS 6001.
The proportions of various elements and the combination
of both components constitute an important feature of the present
inventlon, The desired results intended by the present invention
are not obtainable if the above conditions are no-t met.
Namely, Cu has been known to be an alloy el~rnent capable
of improving the strength oE Al and shifting the potential to a
noble side. However, by an addition o:E Cu the corrosion resis-
tance of an Al alloy is substantiall.y reduced~ Therefore, it is
usual that the amount of Cu added to a corrosion resi.stant ~l
alloy is at most 0~4%, When the Al alloy materi.als are fixed
together by a flux or atmospheric vacuum bra~ing for assemblinc~,
they are heated at a high temperature at a level of from 570 to
61~C in order to melt the ~l-Si bra~ing material, The present
inventors have found that if subjec-ted to such a high temperature
treatment, the Cu element will not thereafter substantially work
to reduce the corrosion resistance and it serves as a strength
improving element and as a potential improving agent.
The range of the amount of Cu added to the main compon-
ent according to the present invention has been determined on the
basis of such as finding, If the amount of Cu is less than 0.2%,
it i.s not possi~le to bring the potential of the base material
1 sufficiently noble and -to attain the desired strength, On -the
other hand, i.f the amount of Cu exceeds 2.0'~, the potential
becomes noble and the strength of the base material is improved,
but the coxrosion resistance tends to decrease. Accordinyly,
in order to improve the strength and the potential withou-t sub-
stantially reducing the corrosion resistance, i-t is necessary to
set the amoun-t of Cu within a range of from 0 2 to 2,0%.
In addition to the Cu element, one or more selected
from the group consisting o:E Zr, Mn and Cr may be added as -the
case requires. Zr :Eorms toge-ther with Al an in-termetallic com-
pound A13Zr which is finely distributed in the ba.se material,
whereby sub-grains are strengthened, and the recrystallization
is suppressed. Accordingly, at the tirne of the rolling and ex-
trusions operation, the metal struc-ture becomes fibrous and the
crystals after a high temperature heating by brazing do not be-
come to be i.some-tric crystals and they become to be flat gains
stretched in the di.rection of working, whereby the diffusion of
Si at the time of brazing is prevented and thus it is possible
to prevent an increase in the intergranular corrosion suscept-
ibility, This efEect is inadequate if -the amount of Zr is less
than 0,01%~ On the other handj if the amount exceeds 0,5%, the
effect is saturated and large precipitates are likely to form
thus leading to degradation of the workability. Thus, the amount
of Zr added should desirably be from 0.01 to 0.5%, as mentioned
above,
Like Zr, Cr and Mn have an effect to strengthen the
subgrains and to suppress the recrystallization, and they also
have an effect to improve the drawability of the base material.
However, like Zr, bot-h of them do not provide adequate effective-
.ness ifth~ir amounts are less than 0.05% and they provide an
.3
1 undesirable effect such that the intergranular corrosion suscept-
ibili-ty of the base material incxeases, if their amounts exceed
0.5~. Thus, they are preferably used in the amounts within -the
ranges specified above.
Referring to the subsidiary componen-t of the present
inven-tion, the reason for setting the proportion of Cu to be a-t
most 0,2% is to prevent the potential from becoming noble. The
difference in the Cu content from that of the main component
should desirably be at least 0.2%~ Further, an alloy to ~e used
for the subsidiary component is selected from the group consisting
of pure Al (lxxx), Al-Mn (3xxx) and Al-Mg-Si (6xxx) alloys~ as
the latter have good corrosion resistance, good brazing property
and high strength.
An Al~Cu (2xxx) alloy has a noble potential and accord-
ingly does not provide a sufficient cathodic corrosion preventive
e:Efect, An Al-Si (4xxx) alloy is not durable at a high temper-
ature heating at the time of brazing, Further, an Al-Mg (5xxx)
alloy and an Al-Zn ~7xxx) alloy bring about a problem that at the
time of vacuum brazing, the Mg element and -the Zn element, respec-
tively~ are evaporated and freed thereby leading to contaminationof the furnace. Thus, these alloys are not suitable as a sacri-
ficial anode material,
Thus~ by setting the various elements of the main com-
ponent and the subsidiary component in the proportions as described
above, it is possible to remarkably improve the corrosion resist-
ance of the heat exchanger,
More specifically, by selectiny the elements and pro-
portions of the elements in the core materia]. and the sacrificial
anode material of the heat exchanger tube according to the pre-
sent invcntion as men-tioned above, it is possible to remar~ably
1 improve the corrosioll res.istallce of -the aluminum heat exchanger
tube
Under the heating condition at the time of brazing, Cu
contained in the core material ~iffuses into the sacrificial anode
material, whereby a concentration gradient is formed by -the dif-
fusion wherein the Cu content is gradually reduced from the core
material to the surface of the sacrificial anode material Thus,
the efect of the sacrificial anode material is thereby enhanced.
The clad rate of such a sacrificial anode material to the core
material varies depending upon the thickness of the core material,
but, for instance, in the case of a sheet material of a thickness
of 0,4 t expected for a radiator tube, it may be about 10~.
Further, it is common to fix the tube with a fin by
brazin~ and if the fin has a brazing material, it is not nece-
ssary to provide a brazing ma-terial to the tube If the fin is
not provided with a brazing material, a braæing material may be
applied to the outer surface of the tube. The brazing material
may be varied in its composition depending upon the method for
brazing. In the case of vacuum bra~ing, an Al-Si-Mg alloy such
as AA400~, or 4104, is used, and in the case of flux brazing, an
Al~Si alloy such as A4343 or A4047 i5 used. ~urther, in the case
of atmospheric brazing, an Al-Si alloy incorporated with other
elements is used.
With respect to the process for the production of tubes,
in the case of a method oE e~trusion and drawing, it is difficult
to form billets, the production costs become expensive, and the
mass production is not feasible. A method of forming and seam
welding sheet or strip materials, is suitable as itgives products
having a quality equivalent to that obtainable by the extrusion
and drawing method and its production costs are less.
1 As the seam welding, there may be mentioned a hiyh frequency
resistance welding or a high fxequency induction welding as typ-
ical examples, bu-t any o-ther suitable method may be used, so long
as a bu-tt-~elding can there~y be done.
Now, the present inven-tion will be described in more
detail with reference to Examples.
_a ple I
Firstly, alloys having the respective compositions as
shown in Table 1 were procured. Nos. 1 to 8 are alloy materials
for the main component of the present invention. Nos. 9 to 11
are comparative materials analogous to the above mentioned alloy
ma-terials~ No, 12 is JIS 3003 alloy.
Further, in the Table, Si, Fe and Ti are all impurities,
and the rest of the alloy elements indicated in the Table is Al.
TABLE
Chemical Compositions of the Alloys
for the Main Component
_ _ __ _ ____
Ou 1 Mn Cr ¦ Zr Si ~e Ti Mg Zn Notes
2~ 1 0.25 0.30.15 0.15 O.lS 0~5 0.03 Materlal
inven-tion
2 0.4 0.3 0.15 0.15 0.5 0.03 .,
3 0.8 0.15 0.5 0.03 ll
4 1.5 0.15 0.15 0.15 0.5 0.03 1.
5 2.0 0.15 0.15 0.15 0.5 0.03 ,~
6 0.8 0~45 0.3 0.07 0.3 0.03 ll
7 0.8 0.3 0.15 0.5 0,03 ,
8 0.8 0.310.15 0,5 0.03 ll
q 0.15 0.8 0,15 0.15 0.5 0.03 Ij CamtPearerial
10 2.5 0.3 0.15~ 0.15 0.15 0.5 jO.03 1 "
11 0.5 1.2 1 0.15 ,0,15 ~0,5 ,0.03
12 0.15 1.2 ~ 0~15 jQ 5 ,0.03 JIS 3003
_
f~
1 To the core materials made of the above alloys, 15o of
a brazing ma-terial composed of ~1, 10% of Si and 1.5% of Mg, is
clad, respec-tively, on both sides thereof, -thereby to obtain
brazing sheets having a -thickness oE 1.2 mm. To these brazing
sheets, fins having the composi-tions shown in Table 1 and having
a thickness of 15 mm were assembled in a manner as shown in
FIGU~E 1, and heating was conducted in vacuum (10 to 10 5 Torr)
at 590C for 3 minutes, whereby test samples were prepared.
These test samples were subjected to CASS Tests according to
JIS H8681. The maxi.mum depths of the corrosion in the brazing
sheets ater the continuous 1000 hours, are shown in Table 1, and
typical examples of the cross sectional shapes are shown in the
photographs (x 1.0) of FIG~RES 2(a~ to (d).
TA ~: 2
Chemical Compositions of The Alloys for
The Subsidiary Component (% by weight~
(the rest being Al)
..... . ... ..
Cu I Mn Cr Zr Si Fe Ti Mc~ ¦ Zn Notes
_ __ ___ ~
21 0.01 ~ 0.07 0.25 0,03 Pure Al
22 0,08j 0.16 0.54 0,03 "
23 0.02l1,16 0.14 0.50 0.03 Al - Mn
2~ 0,16 1.14 0.16 0.53 0.03 "
25 0.01 0.43 0.28 0.030,7 l Al-Mg-Si
26 0,18 11 0.38 0,40 0.03 0.6 l "
27 0.02 0.10~ 0.43 0.031,00
28 0,25 0.3 10~15 0,15 0.15l 0.51 0.03 _ _ Table 1 .
1 TAsLE 3
Maximum Depths of the Corrosion
in The Main Component (B.S.) ~mm) (CASS lOOOH)
S u b s i d i a ry __ I __
¦ NOmponen t I l I
Main Co~ 21 22 23 24 25 ! 26 27 28
ponent ~ L ~
1 0 0.18 0.05 0.21 ! o ~ 0.25 1 0 I Pass-
' , I I through
2 0 0.20 1 0.17 ! 1 0 40
3 0 l 0 35
4 0 0.15 ~ ' 0,12 1 0.40
0 0.21 I 0.21 1 0.38
6 0 0~13 ' I 0.15 1 0.33
7 0 0.1~ ~ 1 0,14 0.51
. 8 0 0.12 1 1 0.11 0.38
9 0.51 Pass- Pass- Pass-
through lthroug~ through
0.530.80 1 l0.68 0.81
2011 0.70Pass- ~ Pass- Pass-
. through; ,throughlthrough
12 0.54 Pass- Pass- Pass- l0.56 0.85 0.40 Pass-
_ through through throus~ l through
It is seen from the photographs that the materials
according to the present invention received relatively light cor-
rosion in all caæs , whereas in the case of the combination of
the 3003 core brazing sheet material and the 3003 fin, which are
conventional materials, an apparent pass-through corrosion was
formed.
~ ~.b~
1 E~ample 2
To the core materials shown in Table 1 of Example 1,
10% oE the Al alloys havincJ the composi-tion shown in Table 2 of
Example 1, were clad, respectively, on both sides thereof, to
obtain aluminum clad ma-terials having a thickness of 0.4 mrn
These aluminum clad materials were heated in vacuo (10 4 to
10 5 Torr) at 595C for 3 minutes, thereby to obtain test samples.
The test samples are immersed in a solution containing 3% of
NaCl and 0.1% of H2O2 and having a pH of 3, at 30C for 7 days,
The maximum depths of the corrosion and the corrosion
states after the tests as cross sectionally observed by a micro-
scope, are shown in Table 4, and the typical examples of the
cross sectional corrosion sta-tes are shown in the photographs
(x 100) of FIG~ES 3(a) to (f).
TABL~ 4
Maximum Depths of Corrosion
in the Main Component
(Aluminum Clad Core Materials) ~mm)
Subsidiary Subsidiary .
Component . Component
Nos. Nos.
Main Com-~\ 21 27 28 Main Com- 21 27 28
ponent \ ponent
Nos. \ Nos.
__ _ ....
1 0 0 Pass- 7 0 0 0,25
through
2 0 0 ll 8 0 0 0.20
3 0 0 0.15 9 0.25 0,21 hrough
4 0 0 0.18 10 Pass- Pass-
through throug
0 0 Pass- 11 Pass- Pass~
through through throug
6 0 0 0.17 1 12 Pass- Pass-
l through throug~
-12-
1 It is seen from the photographs that the corrosion of
the aluminum clad materials according to the present invention
is terminated in the clad layers in all cases, whereas in the
case of the 3003 core material, -the formation of the intergran-
ular corrosion could not be avoided even when various alloys
were clad thereon.
Example _
The alloys shown in Table 1 and Table 2 were formed
into sheets having a thickness of 0,4 mm. These sheets were
heated in vacuo (10 4 to 10 5 Torr) at 595C for 3 minutes, to
obtain test samples. With respect to these samples, natural
electric potentials were measured in a solution of 0.5 N NaCl
open to the atmosphere, at 20C using a saturated calomel elec-
trode as the reference electrode. The electric potentials after
expiration of 24 hours are shown in Table 5. It is seen from
Table 5 that the electric potentials oE the alloys used for the
main component of the present invention are noble in all cases
as compared with the alloys used for the subsidiary component.
-13-
t
1 TABLE _5
Natural. Electric Poten-tials of
The Components (mV, ~s, SCE)
Alloys for -the mains Component i Alloys for the subsidiary
¦ Component
_ _ t -
No. Elec-tric No-tes ¦ No. Electric No-tes
_ potentials ~ _. Potent. ls
1 699 1 21 - 800
2- 693 1 22 - 750
3 - 675 23 - 750
~ Subsidiary
4 - 650 24 - 718 component
Main compon- of the pre-
- 635 present 25 - 760 tion
6 - 673 invention 26 - 747
7 - 673 27 - 780 Comparative
8 - 675 28 - 699 materials
9 - 720
12 630 ~ Comparative
JIS 3003
Further, examples of the aluminum heat exchan~er tubes
according to the present invention will be given toge-ther with
Comparative Examples,
~ ~r co
E~ o o o
o o o
~ -- ~ -- --
Lo h h
~ ~1 ~ ~
o
.._ _ . _ _ ._____._ ___ ___ _
h c
C~ . I
o
_ _ ____ _. ________
~ a~ ~r
_~ ~ ~ o ~
~ ~ o o o
.~ o o o
3 _ ._ ~
~ ~ ~ o ~r
Q ~ ~ o
~\o o
__ _.. _. _____ _ _.__ . _ .
.~ o o
~: ~ o o
~ ~: o o o
~ __ . _ _.____ .____ _.. _ .
E~ o ~r
.
o o o
___ __.~
Ln
.~ .o o
U~
o o CS
I___ _ __ _ _
o ~
~U~ o o
O . . .
_ o o o
. ..... _
' ~
-
~s~
a) O ~ ~ O N Q)
~1 ~O O ~ )
O a~
~ m ~
. _._ __ _ _
--15--
1 Table 6 shows the consti,tuent elements, and their
proportions in the core material, sacrificial anode material and
braziny material for the tubes according to the present invention.
Flat tubes were prepared from these materials by high
frequency inducti.on weldin~,
Thickness of the sheet: 0.4 t
Temper: H 14
Clad rate: 10% of the total thickness in each case of
the sacrificial anode material and the
brazing material 13
Dimension of the tube: 2.5
Welded portion
These tubes were subjected to a compression brea.k down
test using a hydraulic pump. The results thereby obtained are
shown as follows:
n = 1:175 kg/cm2 The welded portions broken
n = 2:177 kg/cm2
n = 3:180 kg/cm2 The non-welded port.ions broken
It is seen from the above results that among the three
tubes, one broke ~t its non-welded portion, and that the other
two tubes broken at their welded portions also have breaking
compression resis-tance almost equivalent to the tube broken at
the non-welded portion, and thus they have adequate strength.
Example 5
TABLE 7
(,% by weight)
¦ Cusi Fe Mn Mg zn Cr Zr ~i
A 0.51 0.057 0.48 0,25 tr0.022 0~151 0.107 0.028
1050 0.002 0.037 0.27 0.00~ 0.001 0.055 _ _ 0.004
303003 0.18 0.044 0.52 1.1~ 0.0070.010 0.002 _ 0.034
17072 0~005 0.032 0,l4 0.00~ 0.003 1.04 tr _ 0.029
-16~
~ .3~
TABLE ~3
_ ~ ___ Co,re ~ C,lad Clad Thickness ,
materials material.s rates of sheets
. _____ .___ _ _,
1. Present ~ 10507~ 0.4 mm
Invention
2. Com-
perative A ~one _
material
3. 3 SC 3003 7Q7210~ ~.
4. " 3003 None _ 0.5 mm
~ - _ _
With use of materials con-taining the elements and hav-
ing the proportions as shown in Table 7, test samples having the
contruc-tions and the shapes as shown in Table 8 were prepared.
These samples were heated in vacuo of 7 x 10 5 Torr
at a temperature correspondiny -to the brazing temperature, and
they ~ere then subjec-ted to a running water tes-t with use of the
apparatus shown in FIGUR~ ~,
Namely, referring to FIGURE ~, city water having a pH
of 7~23~ containing 0.01 ppm o:E Cu and 17,5 ppm o:E Cl and having
an elec-tric.conductivity of 131,0 ~v/cm was supplied to a tank 1
of 100 w x 700 Q x 5Q0 h via a Cu tube 2 of 15 ~ (1 m). Test
pieces S were placed .in a glass tube 3 of 13 ~ x 500 Q provided
at the bottom of the tank 1, and the city wa-ter was led through
the glass tube, The flow rate of the city water was 0,2 m/sec,
and the test was conducted at room temperature of from 15 to 20C
for 30 days,
Development of corrosion due to the tes-t were investi-
gated by the cross sectional micro struc-tures, Namely, the micro-
scopic photographs of the cross sectional micro structures after
the corrosion test are shown in FIGURES 5(.a) to (d), The micro-
scopic pho-tograph of FIGURES 5(a) is a cross sectional micro
r3~
1 structure of the tube according to the present i.nvention. It
is seen that the corrosion is termirlated in the sacrificial anode
material. Whereas, Erorn the cross sec-tional micro structures oE
Comparative materials 2, 3 and 4 as shown in the microscopic
photographs of FIGURES 5~b}, (c) and (d), it is apparent that
the corrosion is propaya-ted in-to the respec-tive core materials
Further, in Table 4, the corrosion rates as calcula-ted
from the reduction of the weights are shown.
TABI,E 9
(MDD)
1. Present invention 1,32
. Comparat,~ve material 2.11
. , , _ _ ,.,, _.. . ~ . . ~
3. Comparative materlal _ ___
- ~ Compara-tive material 2~32
It is seen tha-t the corrosion rate of the tube màterial
according to the present invention is less than those of the
Comparative materials and is lowest amony them, thus indicating
a supperior corrosion resi.stance.
~ Thus, the heat exchanger of the present invention com-
prises a combination oE the main componellt made o:E an alloy hav-
ing the above mentioned specific composition and the subsidi.ary
component made of an alloy compatible with said alloy, whereby
the corrosion resistance as well as the strength and electric
potential, are improved by the synergistic effect oE the alloy
components and by virtue of the good corrosion resistance of the
main component and the good sacrificial.anode effect of the sub-
sidiary component. Thus, it is possible to prevent the breakage
resulting from the corrosion, and to substantially improve the
functional quality over the conventional aluminum heat exchangers.
-18-
~ 3~
1 Expecially, the aluminum heat exchanger tubes of the
present invention havin~ the above mentioned cons-truction, ex-
hibits a superior corrosion resi.stance by virtue of the sacri-
ficial anode even when subiected to a severe condition in which
wa-ter is used, and it also exhibits a superior corrosion resis-
tance even after bra~incj,
--19--
