U.S. patent application number 17/754173 was filed with the patent office on 2022-09-15 for aluminum alloy material and method for manufacturing same.
This patent application is currently assigned to UACJ CORPORATION. The applicant listed for this patent is UACJ CORPORATION. Invention is credited to MIHOKO KIKUCHI, YOSHIHIKO KYO.
Application Number | 20220290304 17/754173 |
Document ID | / |
Family ID | 1000006430939 |
Filed Date | 2022-09-15 |
United States Patent
Application |
20220290304 |
Kind Code |
A1 |
KYO; YOSHIHIKO ; et
al. |
September 15, 2022 |
ALUMINUM ALLOY MATERIAL AND METHOD FOR MANUFACTURING SAME
Abstract
An aluminum alloy material having a base material formed from an
aluminum alloy, and a chemical treatment film on the surface of the
base material. In a cathode polarization curve obtained by
measuring the aluminum alloy material at a sweeping speed of 20
mV/min by using a saturated KCl silver-silver chloride electrode as
a reference electrode in a 5 wt % NaCl static aqueous solution at a
temperature of 25.degree. C. and a pH of 5.5, the electrode
potential at which the absoute value of the current density reaches
10 .mu.A/cm.sup.2 is -1350 to -1150 mV.
Inventors: |
KYO; YOSHIHIKO; (Tokyo,
JP) ; KIKUCHI; MIHOKO; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UACJ CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
UACJ CORPORATION
Tokyo
JP
|
Family ID: |
1000006430939 |
Appl. No.: |
17/754173 |
Filed: |
September 24, 2020 |
PCT Filed: |
September 24, 2020 |
PCT NO: |
PCT/JP2020/035953 |
371 Date: |
March 25, 2022 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 21/06 20130101;
C23C 22/34 20130101; C23C 22/78 20130101 |
International
Class: |
C23C 22/34 20060101
C23C022/34; C22C 21/06 20060101 C22C021/06; C23C 22/78 20060101
C23C022/78 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2019 |
JP |
2019-177015 |
Apr 21, 2020 |
JP |
2020-075335 |
Claims
1. An aluminum alloy material, comprising: a base material made of
an aluminum alloy; and a chemical conversion film on a surface of
the base material, wherein in a cathodic polarization curve
measured on the aluminum alloy material in a 5 wt % NaCl static
aqueous solution at 25.degree. C. having a pH of 5.5 with a
saturated KCl silver-silver chloride electrode as a reference
electrode at a sweep rate of 20 mV/min, an electrode potential at
which an absolute value of a current density reaches 10
.mu.A/cm.sup.2 is -1350 mV to -1150 mV.
2. The aluminum alloy material according to claim 1, wherein the
base material is made of an aluminum alloy containing 0.3 to 5.0%
by weight of Mg.
3. The aluminum alloy material according to claim 1, wherein the
chemical conversion film contains a Ti compound and a Zr compound,
the Ti compound is at least one selected from the group consisting
of Ti oxide and Ti hydroxide, the Zr compound is at least one
selected from the group consisting of Zr oxide and Zr hydroxide,
and a total amount of the Ti compound and the Zr compound in the
chemical conversion film is 2 to 29 mg/m.sup.2 in terms of metal
element amount.
4. A method of manufacturing an aluminum alloy material in which,
in a cathodic polarization curve measured in a 5 wt % NaCl static
aqueous solution at 25.degree. C. having a pH of 5.5 with a
saturated KCl silver-silver chloride electrode as a reference
electrode at a sweep rate of 20 mV/min, an electrode potential at
which an absolute value of a current density reaches 10
.mu.A/cm.sup.2 is -1350 mV to -1150 my, the method comprising:
performing acid etching on a base material made of an aluminum
alloy containing Mg; and applying chemical conversion treatment to
a surface of the base material after the acid etching to form a
chemical conversion film, wherein an etching amount of the base
material in performing acid etching [E: (mg/m.sup.2)] with respect
to a Mg amount in the base material [M (wt %)] satisfies a
relationship of 10 M.ltoreq.E.ltoreq.200 M,
5. The method of manufacturing an aluminum alloy material according
to claim 4, wherein in forming a chemical conversion film, the
chemical conversion treatment is applied by using a treatment
liquid containing a fluorinated titanium compound and a fluorinated
zirconium compound such that a total mass concentration of the
fluorinated titanium compound and the fluorinated zirconium
compound in the treatment liquid [C (ppm, in terms of metal element
amount)] and a treating time [t (seconds)] satisfy
50.ltoreq.C.times.t.ltoreq.1500.
6. The aluminum alloy material according to claim 2, wherein the
chemical conversion film contains a Ti compound and a Zr compound,
the Ti compound is at least one selected from the group consisting
of Ti oxide and Ti hydroxide, the Zr compound is at least one
selected from the group consisting of Zr oxide and Zr hydroxide,
and a total amount of the Ti compound and the Zr compound in the
chemical conversion film is 2 to 29 mg/m.sup.2 in terms of metal
element amount.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a national stage application of
International Patent Application No. PCT/JP2020/035953 filed on
Sept. 24, 2020, which claims the benefit of Japanese Patent
Application No. 2019-177015, filed on Sept. 27, 2019 and Japanese
Patent Application No. 2020-075335, filed on Apr. 21, 2020. The
contents of these applications are incorporated herein by reference
in their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to an aluminum alloy material
and a manufacturing method thereof.
BACKGROUND ART
[0003] To improve surface properties of aluminum alloy materials,
aluminum alloy materials subjected to various surface treatments
have been conventionally proposed. Japanese Patent Application
Publication No. 2014-62277 discloses an aluminum alloy plate,
comprising: an aluminum alloy substrate; and an aluminum oxide film
formed on a surface of the aluminum alloy substrate, wherein the
aluminum oxide film contains at least one additive element having a
P-B ratio (Pilling-Bedworth ratio) of 1.00 or more, 0.01 to 10 atom
% of zirconium, and 0.1 atom % or more and less than 10 atom % of
magnesium.
[0004] Japanese Patent Application Publication No. 2015-206117
discloses a surface-treated aluminum alloy plate to be subjected to
chemical conversion treatment for use, comprising: an aluminum
alloy plate containing magnesium; and an oxide film torined on a
surface of the aluminum alloy plate, wherein the oxide film has a
film thickness of 1 to 30 nm, a concentration of magnesium is 1 to
20 atom %, a concentration of zirconium is 0.2 to 10 atom %, and
each of a concentration of a halogen and a concentration of
phosphorus is less than 0.1 atom %.
SUMMARY OF DISCLOSURE
Technical Problem
[0005] Aluminum alloy materials subjected to various surface
treatments have been conventionally proposed, but an aluminum alloy
material in which electrochemical activity of a surface is
controlled has not been sufficiently investigated. The present
inventors have made intensive investigation to solve the above
problem, and as a result, have found that an aluminum alloy
material having reduced electrochemical activity of a surface can
be obtained by performing a specific surface treatment on the
surface of a base material. The present inventors have found that
deterioration of a boundary with another material is unlikely to
occur in such an aluminum alloy material, and adhesion durability
between the aluminum alloy material and the other material is
improved to complete the present disclosure. That is, the present
disclosure provides an aluminum alloy material having excellent
adhesion durability to another material and a manufacturing method
thereof.
Solution to Problem
[0006] To solve the above problem, the present disclosure has the
following aspects.
[1] An aluminum alloy material, including: a base material made of
an aluminum alloy; and a chemical conversion film on a surface of
the base material, wherein
[0007] in a cathodic polarization curve measured on the aluminum
alloy material in a 5 wt % NaCl static aqueous solution at
25.degree. C. having a pH of 5.5 with a saturated KCl silver-silver
chloride electrode as a reference electrode at a sweep rate of 20
mV/min, an electrode potential at which an absolute value of a
current density reaches 10 .mu.A/cm.sup.2 is -1350 mV to -1150
mV.
[2] The aluminum alloy material according to the above [1], wherein
the base material is made of an aluminum alloy containing 0.3 to
5.0 % by weight of Mg. [3] The aluminum alloy material according to
the above [1], wherein
[0008] the chemical conversion film contains a Ti compound and a Zr
corn pound,
[0009] the Ti compound is at least one selected from the group
consisting of Ti oxide and Ti hydroxide,
[0010] the Zr compound is at least one selected from the group
consisting of Zr oxide and Zr hydroxide, and
[0011] a total amount of the Ti compound acrd the Zr compound in
the chemical conversion film is 2 to 29 mg/m.sup.2 in terms of
metal element amount.
[4] A method of manufacturing an aluminum alloy material in which,
in a cathodic polarization curve measured in a 5 wt % NaCl static
aqueous solution at 25.degree. C. having a pH of 5.5 with a
saturated KCl silver-silver chloride electrode as a reference
electrode at a sweep rate of 20 V/min, an electrode potential at
which an absolute value of a current density reaches 10
.mu.A/cm.sup.2 is -1350 mV to -1150 mV, the method comprising:
[0012] performing acid etching on a base material made of an
aluminum alloy containing Mg; and
[0013] applying chemical conversion treatment to a surface of the
base material after the acid etching to form a chemical conversion
film, wherein
[0014] an etching amount of the base material in performing acid
etching [E: (mg/m.sup.2)] with respect to a Mg amount in the base
material [M (wt %)] satisfies a relationship of 10
M.ltoreq.E.ltoreq.200 M.
[5] The method of manufacturing an aluminum alloy material
according to the above [4], wherein in forming a chemical
conversion film, the chemical conversion treatment is applied by
using a treatment liquid containing a fluorinated titanium compound
and a fluorinated zirconium compound such that a total mass
concentration of the fluorinated titanium compound and the
fluorinated zirconium compound in the treatment liquid [C (ppm, in
terms of metal element amount)] and a treating time [t (seconds)]
satisfy 50.ltoreq.C.times.t.ltoreq.1500. [6] The aluminum alloy
material according to the above [2], wherein
[0015] the chemical conversion film contains a Ti compound and a Zr
compound,
[0016] the Ti compound is at least one selected from the group
consisting of Ti oxide and Ti hydroxide,
[0017] the Zr compound is at least one selected from the group
consisting of Zr oxide and Zr hydroxide, and
[0018] a total amount of the Ti compound and the Zr compound in the
chemical conversion film is 2 to 29 mg/m.sup.2 in terms of metal
element amount.
Effects of Disclosure
[0019] The present disclosure can provide an aluminum alloy
material having excellent adhesion durability to another material
and a manufacturing method thereof.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1A A diagram illustrating a front face view of a
plate-shaped aluminum alloy material provided for measurement of a
cathodic polarization curve.
[0021] FIG. 1B A diagram illustrating a rear face view of a
plate-shaped aluminum alloy material provided for measurement of a
cathodic polarization curve.
[0022] FIG. 2 A graph indicating a cathodic polarization curve of
an aluminum alloy material of Example 2.
DESCRIPTION OF EMBODIMENTS
[0023] 1. Aluminum Alloy Material
[0024] An aluminum alloy material of the present disclosure
comprises: a base material made of an aluminum alloy; and a
chemical conversion film on a surface of the base material. In a
cathodic polarization curve measured on the aluminum alloy material
in a 5 wt % NaCl static aqueous solution at 25.degree. C. having a
pH of 5.5 with a saturated KCl silver-silver chloride electrode as
a reference electrode at a sweep rate of 20 mV/min, an electrode
potential at which an absolute value of a current density reaches
10 .mu.A/cm.sup.2 is -1350 mV to -1150 mV.
[0025] For example, in a case where a conventional aluminum alloy
material is adhered to another member via an adhesive (another
material), when a tensile stress is applied to a boundary between
the aluminum alloy material and the adhesive with use,
deterioration of the adhesion boundary between the aluminum alloy
material and the adhesive (boundary deterioration) proceeds. A
cause of the occurrence of the boundary deterioration is corrosion
of the aluminum alloy material due to permeation of moisture or
salinity from an end face of the adhesion, or growth of an oxide
film on the surface due to a reaction between the permeated
moisture and the aluminum alloy material. The permeation of
moisture gradually occurs from the adhesion boundary, and also
occurs by passing water vapor through the adhesive. In addition, in
an environment of practical use of the adhesive, the adhered part
is under a state where a tensile stress is persistently applied,
and exposed to a corrosive environment at the same time. That is,
both of mechanical deterioration of physically cleaving the
adhesion boundary and chemical deterioration of permeating moisture
and salinity into the adhesion boundary occur at the same time, and
it is found to be a strict deteriorative environment exceeding a
conventional presumption. As a result, with a conventional surface
treatment method, the adhesion durability in such a strict
environment is insufficient.
[0026] In contrast, by controlling electrochemical property on a
surface within an appropriate range, the aluminum alloy material of
the present disclosure can inhibit that the boundary between the
aluminum alloy material and the adhesive is deteriorated due to
application of the tensile stress and corrosion and deteriorated
due to permeation of moisture, salinity, and the like. The
electrochemical property on the surface of the aluminum alloy
material can be measured by measurement of a polarization curve. In
a cathodic polarization curve of the aluminum alloy material of the
present disclosure, an electrode potential at which an absolute
value of a current density reaches 10 .mu.A/cm.sup.2 is --1350 mV
to -1150 mV. Since the aluminum alloy material of the present
disclosure has the characteristic of the cathodic polarization
curve as above even when forming a boundary with a material other
than the adhesive, the aluminum alloy material of the present
disclosure can inhibit the boundary deterioration due to
application of tensile stress, corrosion, or permeation of
moisture, salinity, and the like.
[0027] A mechanism in which the electrochemical property on the
surface of the aluminum alloy material affects the boundary
deterioration is as follows. On the surface of the aluminum alloy,
a dense natural oxide film generated by a reaction with the air and
water and having a thickness of several nanometers is present.
Since this natural oxide film is insulative and highly protective,
corrosion resistance of the aluminum alloy is achieved. However,
there are defect parts on the natural oxide film, and it is known
that the defect parts become starting points of occurrence of
corrosion. During occurrence of corrosion of the aluminum alloy,
the following anode reaction and cathode reaction simultaneously
proceed.
(Anode Reaction) Al.fwdarw.Al.sup.3++3e.sup.- (Cathode Reaction)
O.sub.2+2H.sub.2O+4e.sup.-.fwdarw.4OH.sup.- [0028]
2H.sup.30+2e.sup.-.fwdarw.H.sub.2
[0029] This is because electrons generated by ionization
(dissolution) of aluminum metal, which is the anode reaction, are
required to be consumed by the cathode reaction (reduction reaction
of dissolved oxygen or protons) to satisfy the electrically neutral
condition. As described above, the defect parts present on the
natural oxide film on the surface of the aluminim alloy act as
active sites where these anode reaction and cathode reaction occur.
However, among these defect parts on the film, defect parts which
function as the site of the cathode reaction are limited to a
precipitated product or the like that is present on the surface of
the aluminum alloy and that has a high potential. That is, the
corrosion of the aluminum alloy is rate-determined by a degree of
activity of the cathode reaction (cathode activity) on the surface.
A reaction between the surface of the aluminum alloy and moisture
continues to grow the surface oxide film, and this is also the same
mechanism as the above. Therefore, to effectively inhibit the
deterioration of the adhesion boundary, it is effective to
appropriately control the electrochemical property on the surface
of the aluminum alloy, specifically the cathode activity.
[0030] When the cathode activity on the surface of the aluminum
alloy is high, the corrosion reaction is likely to occur on the
surface of the aluminum alloy, and enhances the deterioration of
the adhesion boundary. Thus, by forming a chemical conversion film
on the surface of the aluminum alloy with chemical conversion
treatment, the cathode activity on the surface can be appropriately
reduced, and the deterioration of the adhesion boundary can be
inhibited. however, when an unnecessarily thick film is formed on
the surface of the aluminum alloy due to an excessive chemical
conversion treatment, the cathode activity on the surface is
significantly reduced, but deterioration of the chemical conversion
film itself and breakage or peeling in the chemical conversion film
are likely to occur, leading to decrease in the adhesion
durability. In the present disclosure, by preferably regulating the
electrochemical characteristic on the surface of the aluminum
alloy, the deterioration of the adhesion boundary and the decrease
in the adhesion durability can be inhibited. Here, the
electrochemical characteristic on the surface of the aluminum alloy
can be evaluated by measurement of a polarization curve.
[0031] in a cathodic polarization curve of the aluminum alloy
material of the present disclosure, an electrode potential at which
an absolute value of a current density reaches 10 .mu.A/cm.sup.2 is
-1350 mV to -1150 mV. In the cathodic polarization curve of the
aluminum alloy material of the present disclosure, when the
electrode potential at which the absolute value of the current
density reaches 10 .mu.A/cm.sup.2 is higher than -1150 mV, the
inhibition of the cathode activity on the surface of the aluminum
alloy is insufficient, and the adhesion durability decreases. The
electrode potential herein is, unless specifically described, a
value measured with a saturated KCl silver-silver chloride
electrode (SSE) at 25.degree. C. as a reference electrode. In
addition, in the cathodic polarization curve of the aluminum alloy
material of the present disclosure, when the electrode potential at
which the absolute value of the current density reaches 10
.mu.A/cm.sup.2 is lower than -1350 mV, the formed chemical
conversion film is unnecessarily thickened, leading to decrease in
the adhesion durability. Therefore, it is preferable that the above
electrode potential be -1330 mV to -1175 mV, and it is more
preferable that the above electrode potential be -1310 mV to -1200
mV. In the cathodic polarization curve, the electrode potential at
which the absolute value of the current density reaches 10
.mu.A/cm.sup.2 being within the above range allows the aluminum
alloy material to have more excellent adhesion durability. In
addition, by performing the appropriate surface treatment on the
base material made of the aluminum alloy, the electrochemical
characteristic on the surface can be controlled, and in the
cathodic polarization curve, the electrode potential at which the
absolute value of the current density eaches 10 .mu.A/cm.sup.2 can
be controlled within the above range. Specifically, by
appropriately controlling each condition of acid etching and
chemical conversion treatment as the above surface treatment, and a
treatment associated with these surface treatments, if necessary,
the electrochemical characteristic on the surface of the aluminum
alloy material can be optimized,
[0032] The cathodic polarization curve of the aluminum alloy
materil of the present disclosure is measured as follows. First, a
container opened to the atmosphere at 25.degree. C. is prepared,
300 ml of a 5 mass % NaCl aqueous solution at 25.degree. C. having
a pH of 5.5 is poured into the container, and left to stand. At
this time, the pH of the NaCl aqueous solution can be adjusted to
be a pH of 5.5 by using NaOH or HCl The container used for the
measurement is not particularly limited as long as it has a depth
that can sufficiently immerse the material to be measured and it
has no excessive aspect ratio (ratio between the diameter of the
bottom face and the height of the container), and as an example, a
beaker having a volume of 500 ml is appropriate. FIG. 1A
illustrates a front face view of a plate-shaped aluminum alloy
material provided for the measurement of the cathodic polarization
curve, and FIG. 1B illustrates a rear face view of a plate-shaped
aluminum alloy material provided for the measurement of the
cathodic polarization curve. As illustrated in FIGS. 1A and 1B, the
aluminum alloy provided for the measurement is cut to plate-shaped
specimens with 5 cm.times.2 cm by using shears. Among the
specimens, a specimen without a scar nor a smear is selected. At a
position distanced with approximately 5 mm from one end in the
longitudinal direction of the plate-shaped specimen 10, a surface
to be measured with 1 cm.times.1 cm is exposed (the surface to be
measured is provided at one position on only the front face of the
specimen), and the remainder part is masked with a silicone resin
to determine an evaluation area 11. At this time, on the opposite
side to a part of the evaluation area 11, one end 12 in the
longitudinal direction of the specimen is exposed with
approximately 5 mm, and a terminal for the measurement is
connected. Thereafter, the material to be measured and a counter
electrode (platinum electrode) are immersed in the NaCl aqueous
solution, and left to stand for 30 minutes. At this time, an
approximately half in the longitudinal direction of the material to
be measured is immersed under the solution level. At this time, the
material to be measured is immersed so that a contacting part with
the measurement terminal is not wet and so that the measurement
surface is immersed under the solution level with 1 cm or longer.
The platinum electrode is not particularly limited as long as it is
used for a usual potentiodynamic polarization measurement, and as
an example, a method in which a platinum wire with 0.7 mm in
diameter and 120 mm in length is used and immersed under the
solution level with 5 cm or longer in the measurement can be
mentioned. During the measurement, degassing and stirring are not
performed. As a reference electrode, a saturated KCl silver-silver
chloride electrode (HS-205C, manufactured by DKK-TOA CORPORATION)
at 25.degree. C. is used, and the polarization curve is measured
with a three-electrode method. After 30 minutes from starting the
immersion of the material to be measured, the potential is swept
from a spontaneous potential of the material to be measured into
the lower direction with a potentiostat (SDPS-511U, manufactured by
Syrinx. Inc) to measure the cathodic polarization curve. At this
time, the sweep rate of the potential is set to be 20 mV min. Then,
the electrode potential at which the absolute value of the current
density has reached 10 .mu.A/cm.sup.2 is measured. Here, the
absolute value of the current density being 10 .mu.A/cm.sup.2 means
that the cathode current density becomes 10 .mu.A/cm.sup.2 with
considering of removing the plus or minus sign from the measured
current value. For example, with a measurement apparatus indicating
a cathode current as minus, the measured value of the cathode
current density is indicated as -10 .mu.A/cm.sup.2; thus, the minus
sign is removed to be 10 .mu.A/cm.sup.2. The evaluation area 11 of
the material to be measured is accurately measured, and the
measured current is divided by the actual evaluation area 11 to
calculate the current density. It is desired that the above
measurement be performed on three different materials to be
measured to determine an averaged value thereof. With determining
the potential at which the current density has reached 10
.mu.A/cm.sup.2, a case where the current density instantaneously
has reached 10 .mu.A/cm.sup.2 with noise or the like is ignored as
an abnormal value. Thus, it is required that the polarization be
performed until the potential at which the current density
sufficiently exceeding 10 .mu.A/cm.sup.2 can be confirmed, and it
is desired that the measurement be performed to -1600 mV or
lower.
[0033] Hereinafter, each part forming the aluminum alloy material
according to an embodiment will be described.
[0034] (Base Material)
[0035] The base material is not particularly limited as long as it
is made of an aluminum alloy, and can be a base material made of
1000-series aluminum alloy (pure aluminum alloy), 2000-series
aluminum alloy (Al-Cu-Mg-based aluminum alloy), 3000-series
aluminum alloy (Al-Mn-based aluminum alloy), 4000-series aluminum
alloy (Al-Si-based aluminum alloy), 5000-series aluminum alloy
(Al-Mg-based aluminum alloy), 6000-series aluminum alloy
(Al-Mg-Si-based alloy), 7000-series aluminum alloy (Al-Zn-Mg-based
aluminum alloy), and the like. From the viewpoints of strength and
corrosion resistance of the base material made of the aluminum
alloy, it is preferable that an aluminum alloy containing 0.3 to
5.0 % by weight of Mg be used.
[0036] (Chemical Conversion Film)
[0037] The chemical conversion film is a film obtained by applying
chemical conversion treatment, described later, to the surface of
the base material. It is preferable that the chemical conversion
film contain an inorganic compound, and it is more preferable that
the chemical conversion film contain a Ti compound and a Zr
compound. It is preferable that the Ti compound be at least one of
Ti oxide and Ti hydroxide, and it is preferable that the Zr
compound be at least one of Zr oxide and Zr hydroxide. When the
chemical conversion film contains the Ti compound and the Zr
compound, it is preferable that a total amount of the Ti compound
and the Zr compound in the chemical conversion film be 2 to 29
mg/m.sup.2, it is more preferable that it be 3 to 27 mg/m.sup.2,
and it is further preferable that it be 4 to 20 mg/m.sup.2, in
terms of metal element amount. The total amount of the Ti compound
and the Zr compound being within the above range allows the
aluminum alloy material to have excellent adhesion durability. It
is preferable that each amount of the Ti compound and the Zr
compound be at least 1 mg/m.sup.2, and it is more preferable that
it be at least 1.5 mg/m.sup.2, in terms of metal element amount.
The above "in terms of metal element amount" refers to amounts of
Ti element and Zr element per m.sup.2 of the chemical conversion
film. It is preferable that a film thickness of the chemical
conversion film be less than 50 nm, it is more preferable that it
be less than 30 nm and it is further preferable that it be 1 nm to
20 nm. The total amount of the Ti element and the Zr element per
m.sup.2 of the chemical conversion film can be measured by
preparing a calibration curve based on a reference plate having a
known amount of the film with an X-ray fluorescence spectrometer
(XRF). The film thickness of the chemical conversion film can be
measured with GD-OES (Glow Discharge Optical Emission
Spectroscopy). When a value at which an emission intensity of
aluminum has sufficiently reached a balk (base material) is set to
a reference, the spattering depth at which the emission intensity
reaches 50 % of the reference value is specified as the film
thickness.
[0038] 2. Method of Manufacturing Aluminum Alloy Material
[0039] In a method of manufacturing the aluminum alloy material of
the present disclosure, manufactured is an aluminum alloy material
in which, in a cathodic polarization curve measured in a 5 wt %
NaCl static aqueous solution at 25.degree. C. having a pH of 5.5
with a saturated KCl silver-silver chloride electrode as a
reference electrode at a sweep rate of 20 mV/min, an electrode
potential at which an absolute value of a current density reaches
10 .mu.A/cm.sup.2 is -1350 mV to -1150 mV. The manufacturing method
includes: performing acid etching on a base material made of an
aluminum alloy containing Mg; and applying chemical conversion
treatment to a surface of the base material after the acid etching
to form a chemical conversion film. The acid etching is performed
so that an etching amount of the base material in performing acid
etching [E: (mg/m.sup.2)] with respect to a Mg amount in the base
material [M (wt %)] satisfies a relationship of 10
M.ltoreq.E.ltoreq.200 M. In the aluminum alloy material
manufactured with the method of manufacturing the aluminum alloy
material of the present disclosure, in the cathodic polarization
curve, the electrode potential at which the absolute value of the
current density reaches 10 .mu.A/cm.sup.2 is -1350 mV to -1150 mV.
Thus, it can be inhibited that the boundary between the aluminum
alloy material and the adhesive deteriorates due to application of
tensile stress and corrosion, and it can be inhibited that it
deteriorates due to permeation of moisture, salinity, and the like.
Since the aluminum alloy material of the present disclosure has the
characteristic of the cathodic polarization curve as above even
when forming a boundary with a material other than the adhesive,
the aluminum alloy material of the present disclosure can inhibit
the boundary deterioration due to application of tensile stress,
corrosion, or permeation of moisture, salinity, and the like. In
addition, The E being 10 M or more allows the surface of the base
material after the acid etching to be clean, and to form a chemical
conversion film well adhered to the surface of the base material.
In contrast, when the E exceeds 200 M and becomes excessively
large, a surface roughness generated by the etching and smut (a
fine particle powder of an insoluble substance by an acid remained
after the etching) affect the adhesion durability. This is
presumably because the smut enters the inside of the surface
roughness and becomes not easily removed to affect adhesiveness to
the adhesive. Accordingly, the E being 200 M or less can inhibit an
unnecessary increase in the surface roughness and excessive
generation of the smut, and can improve the adhesion durability
between the aluminum alloy material and the other material.
Hereinafter, each step of the method of manufacturing the aluminum
alloy material of the present disclosure will be described in
detail.
[0040] (Rolling and Heat Treatment)
[0041] As an example, after the aluminum alloy is formed to be an
ingot according to a common method, a homogenizing treatment, a
heat rolling, a cold rolling, an intermediate annealing, and a cold
rolling, or a homogenizing treatment, a heat rolling, and a cold
rolling are performed in this order, and an aluminum alloy plate
that is rolled to have a final plate thickness is used as the base
material. Thereafter, a heat treatment is performed on the aluminum
alloy plate that is rolled to have the final plate thickness. At
this time, when the heat treatment is performed in the atmosphere,
magnesium, which is an easily oxidized element, in the aluminum
alloy diffuses to the surface to be bonded to oxygen, and a layer
containing a large amount of magnesium oxide is formed on the
surface of the aluminum alloy plate.
[0042] (Degreasing Step)
[0043] Before performing acid etching, a degreasing step may be
optionally performed. This is for a purpose of removing a rolling
oil, a processing oil, a lubricant, and the like that adhere to the
surface of the aluminum alloy plate in the step before acid
washing. A solution used in this washing step is not particularly
limited, and an alkaline washing agent, a surfactant, or a mixed
liquid thereof, or an organic solvent is preferably used, and after
that, a water washing step is performed. When an amount of oil that
adheres to the surface of the aluminum alloy plate is small, the
washing step may be omitted. When the degreasing step is performed
and when an alkaline degreasing agent is used, dissolution of a
certain amount of the aluminum alloy of the base material occurs.
When the dissolution amount of the base material in the washing
step is too large, a large amount of smut adheres to the plate
surface, and may affect the following step. Thus, when the
degreasing step is performed, it is preferable that the dissolution
amount of the aluminum alloy be set to be 50 mg/m.sup.2 or less,
and it is more preferable that it be 40 mg/m.sup.2 or less. Since
an etching with an alkali cannot remove a substance having a low
solubility in the alkali, such as magnesium oxide on the surface of
the aluminum alloy plate, an alkali etching cannot be a replacement
for the acid etching step.
[0044] (Performing Acid Etching)
[0045] In performing acid etching, the acid etching is performed on
the base material made of the aluminum alloy containing Mg. The
condition of performing acid etching is not particularly limited as
long as it is a condition in that the etching amount of the base
material [E: (mg/m.sup.2)] with respect to an amount of Mg in the
base material before the acid etching [M (wt %)] satisfies a
relationship of 10 M.ltoreq.E.ltoreq.200 M. Performing the acid
etching under the condition satisfying the relationship of 10
M.ltoreq.E.ltoreq.200 M can remove a vulnerable layer present on
the surface of the aluminum alloy base material, and can improve
the adhesion durability. The vulnerable layer is a surface-modified
layer generated by mechanical processing such as the rolling step
and a mixture of aluminum oxide or magnesium oxide grown on the
surface of the aluminum alloy in the heat treatment step. When the
adhesion is performed in a state where these vulnerable layers
remain,, the adhesion durability decreases. In an aluminum alloy
containing a large amount of magnesium, which is an easily oxidized
element, magnesium oxide is likely to be generated in the heat
treatment step, and the vulnerable layer tends to be formed
thickly. Here, to optimize the etching amount according to the
content of a magnesium alloy in the base material, E/M is set to be
10 to 200. It is preferable that E/M be 20 to 150, and it is more
preferable that E/M be 30 to 100. It is preferable that M be 0.3 to
5.0 wt %, it is more preferable that M be 1.0 to 5.0 wt %, and it
is further preferable that M be 2.0 to 5.0 wt %. The Mg amount in
the base material before the etching can be measured by emission
spectroscopy in accordance with H 1305:2005, but it may be any
method that can obtain a similar level of accuracy. When a
manufactured base material is purchased, the Mg amount can be
calculated from a nominal Mg content of the base material. The
etching amount E of the base material can be calculated by: using a
material to be measured in which the base material is cut in an
appropriate size; measuring dry masses before and after the
etching; and dividing a difference in the measured results (mass
before etching--mass after etching) by the area of the material to
be measured to be converted into a numerical value per unit area.
At this time, the size of the material to be measured may be any,
but when the area is small, a change in the weight becomes small,
and affects the measurement accuracy. Thus, it is required that the
area of the material to be measured be set to an appropriate size
with considering accuracy of a balance used for weighing. As an
etching liquid for the acid etching, an acid of nitric acid,
sulfuric acid, hydrofluoric acid phosphoric acid, or a mixed
solution thereof can be used. The etching liquid may optionally
contain an etching auxiliary (oxidizing agent), a surfactant, a
chelating agent, and the like. It is preferable that a
concentration of the acid in the etching liquid (in case of the
mixed solution, a total concentration of each acid solution) be
0.01% by weight to 30% by weight, it is more preferable that it be
0.03% by weight to 25% by weight, and it is further preferable that
it be 0.05% by weight to 20% by weight. It is preferable that a
temperature of the etching liquid be 30 to 90.degree. C., it is
more preferable that it be 40 to 90.degree. C., and it is further
preferable that it be 45 to 90.degree. C. It is preferable that a
time of the etching be 1 second to 30 seconds, it is more
preferable that it be 1 to 25 seconds, and it is further preferable
that it be 1 to 20 seconds. It is preferable that a water washing
step be performed after the acid etching step. In the water washing
step, it is preferable that water having an electroconductivity at
a temperature of 20.degree. C. of 500 mS/m or less be used. When
water having a high electroconductivity is used, each ion contained
in the water is absorbed on the surface of the aluminum alloy, and
may be a cause of decrease in the adhesion durability. It is
preferable that a temperature of water in the water washing step be
30.degree. C. to 90.degree. C., it is more preferable that it be
40.degree. C. to 85.degree. C., and it is further preferable that
it be 45.degree. C. to 80.degree. C. This is because solubility of
many substances increases in water with a higher temperature and it
is effective for washing the surface of the aluminum alloy base
material after the etching. The higher the temperature of the
washing water, the higher the washing effect, but it may cause an
increase in energy cost, When the temperature of washing water is
higher than 90.degree. C., a hydration reaction of the aluminum
alloy base material with water may occur to form a hydrated oxide
film of the aluminum on the surface. In addition, when the time of
the water washing step is too long, the aluminum surface and the
washing water may gradually react to form an oxide of aluminum.
When the time of the water washing step is too short, a treating
reagent liquid adhering to the surface cannot be sufficiently
removed in some cases. Thus, it is preferable that the time of the
water washing step be 0.5 seconds to 30 seconds, and it is more
preferable that it be 1 second to 20 seconds.
[0046] (Forming Chemical Conversion Film)
[0047] In forming a chemical conversion film, the chemical
conversion treatment is applied to the surface of the base material
after the acid etching to form the chemical conversion film.
Although many sites of the cathode reaction are present on the
surface after the acid etching step, the adhesion durability can be
improved by forming an appropriate chemical conversion film. As the
chemical conversion film, a film formed by an electrochemical
reaction between ions dissolved in a treatment liquid and the
surface of the aluminum alloy is good, and thereby, an inorganic
material-based chemical conversion film is preferable. This is
because the sites of the cathode reaction present on the surface of
the aluminum alloy base material act as sites that are likely to
cause the film formation also in the process of forming the
chemical conversion film. Thus, when the chemical conversion film
is formed by the electrochemical reaction between the dissolved
ions in the solution and the aluminum alloy, the cathode reaction
sites on the surface of the aluminum alloy can be efficiently
covered. Among the inorganic material-based chemical conversion
films, in particular, a film containing both titanium and zirconium
is preferable. This is because an oxide or hydroxide of titanium
and an oxide or hydroxide of zirconium that are formed as the
chemical conversion film are chemically stable, and a chemical
change is unlikely to occur even in a deteriorative environment and
it is effective for preventing decrease in the adhesion durability.
In forming the chemical conversion film on the surface of the
aluminum alloy base material, since the film formation gradually
proceeds from the cathode reaction sites on the surface, as
described above, the electrochemical characteristic on the surface
of the aluminum alloy changes moment by moment in this process.
Thus, by blending titanium and zirconium, which are elements having
different solubility and electrode potential in the solution each
other in the treatment liquid, it can widely manage the surface of
the aluminum alloy that changes moment by moment during the process
of forming the chemical conversion film, and it can cover the
surface of the aluminum alloy with the chemical conversion film
efficiently and most appropriately.
[0048] It is preferable that no drying nor air blowing be performed
between the water washing step in the acid etching step and the
step of forming a chemical conversion film and that the surface of
the aluminum alloy be a state of wetted with the washing water.
This is to prevent that each oxide on the surface of the aluminum
alloy removed in the acid etching step grows again thickly by
contacting the air. However, with contacting the washing water in a
long time, each oxide begins to grow on the surface of the aluminum
alloy. Thus, from the end of the water washing step in the acid
etching step, it is preferable that the step of forming a chemical
conversion film be begun within 30 seconds, it is more preferable
that it be begun within 10 seconds, and it is further preferable
that it be begun within 5 seconds. it is most preferable that it be
begun within 2 seconds.
[0049] In forming a chemical conversion film, it is preferable that
the chemical conversion treatment be applied by using a treatment
liquid containing a fluorinated titanium compound and a fluorinated
zirconium compound such that a total mass concentration of the
fluorinated titanium compound and the fluorinated zirconium
compound in the treatment liquid [C (ppm, in terms of metal element
amount)] and a treating time [t (seconds)] satisfy
50.ltoreq.C.times.t.ltoreq.1500. The C.times.t being within the
above range can form the chemical conversion film most suitable for
the surface of the aluminum alloy after the acid etching step. As
the fluorinated titanium compound, hexafluorotitanic acid
(H.sub.2TiF.sub.6), salts thereof (particularly, a potassium salt,
a sodium salt, and an ammonium salt), and the like can be
mentioned. As the fluorinated zirconium compound,
hexafluorozirconic acid (H.sub.2ZrF.sub.6), salts thereof
(particularly, a potassium salt, a sodium salt, and an ammonium
salt), and the like can be mentioned.
50.ltoreq.C.times.t.ltoreq.1500 is preferable,
80.ltoreq.C.times.t.ltoreq.1400 is more preferable, and
100.ltoreq.C.times.t.ltoreq.1300 is further preferable. When the
C.times.t is less than 50, the chemical conversion film cannot be
sufficiently formed on the surface of the aluminum alloy in some
cases. When the C.times.t exceeds 1500, the chemical conversion
film is formed much thickly to cause decrease in the adhesion
durability in some cases. It is preferable that the total mass
concentration C (in terms of metal element amount) of the
fluorinated titanium compound and the fluorinated zirconium
compound in the treatment liquid be 20 to 400 ppm, it is more
preferable that it be 30 to 350 ppm, and it is further preferable
that it be 40 to 300 ppm. It is preferable that the time t be 0.5
to 30 seconds, it is more preferable that it be 1 to 25 seconds,
and it is further preferable that it be 1.5 seconds to 20 seconds.
It is preferable that a mass concentration of the fluorinated
titanium compound in the treatment liquid in terms of metal element
be 10 to 400 ppm, it is more preferable that it be 15 to 300 ppm,
and it is further preferable that it be 20 to 200 ppm. It is
preferable that a mass concentration of the fluorinated zirconium
compound in the treatment liquid be 10 to 400 ppm, it is more
preferable that it be 15 to 300 ppm, and it is further preferable
that it be 20 to 200 ppm. It is preferable that a temperature of
the treatment liquid be 30 to 80.degree. C., it is more preferable
that it be 35 to 70.degree. C., and it is further preferable that
it be 40 to 65.degree. C. When the concentrations of the
fluorinated titanium compound and fluorinated zirconium compound in
the treatment liquid, the treating time, and the treating
temperature are within the above range, and when the [C (ppm, in
terms of metal element amount)] and the treating time [t (seconds)]
are within the above range, the chemical conversion film on the
surface of the aluminum alloy can be adhered most
appropriately.
[0050] As the treating area of the aluminum alloy base material
increases, Al ions eluted from the base material gradually increase
in the treatment liquid for the chemical conversion treatment. When
the Al ions increase, it becomes a cause of inhibiting the film
formation of the chemical conversion film. The Al ion concentration
in the treatment liquid of up to approximately 800 ppm does not
affect the film formation of the chemical conversion film, but it
is preferable that the Al ion concentration in the treatment liquid
be 600 ppm or less, and it is more preferable that it be 500 ppm or
less.
[0051] As an example, after forming a chemical conversion film, the
water washing step is further performed immediately. This step
rapidly removes the treatment liquid remained on the surface and
controls the time of the reaction between the base material surface
and the treatment liquid to be able to appropriately regulate the
thickness of the chemical conversion film. Furthermore, this step
can prevent that the component in the treatment liquid remains on
the surface of the chemical conversion film. When the component in
the treatment liquid remains on the surface of the chemical
conversion film, it becomes a cause of decrease in the adhesion
durability and occurrence of discoloration on the base material
surface. It is preferable that the time from the step of forming a
chemical conversion film to the water washing step be within 2
seconds, and it is more preferable that it be within 1 second. For
the water used in the water washing step, it is preferable that an
electroconductivity at a temperature of 20.degree. C. be set to be
100 mS/m or less, and it is more preferable that it be set to be 50
mS/m or less. When water having a high electroconductivity is used,
each ion contained in the water remains on the base material
surface, and it becomes a cause of decrease in the adhesion
durability and occurrence of discoloration on the base material
surface. For the measurement of the electroconductivity, for
example, an alternating-current two-terminal method and the like
can be used.
[0052] Since the water washing step after forming a chemical
conversion film affects the final quality of the base material
surface, it is desirable that two or more times, a plurality times,
of the water washing steps be provided. When the plurality times of
the water washing steps after forming a chemical conversion film
are provided, it is preferable that an interval between each of the
water washing steps be within 2 seconds, and it is further
preferable that it be within 1 second. it is preferable that the
electroconductivity of water used in the water washing step
performed after the first water washing step be the same as or
lower than the electroconductivity of the water used in the first
water washing step after forming a chemical conversion film. This
can sufficiently remove a component in the chemical treatment
liquid that is not removed in the first water washing step. When
the time of the water washing step is too long, the surface of the
aluminum alloy base material and the washing water gradually react,
and an oxide of aluminum may be formed. When the time of the water
washing step is too short, the washing effect cannot be
sufficiently obtained. Thus, it is preferable that a total time of
the water washing steps performed after forming a chemical
conversion film be 0.5 seconds to 30 seconds, and it is more
preferable that it be 1 second to 20 seconds. Since solubility of
many substances increases in water a higher temperature, the higher
the temperature of water in the water washing step after forming a
chemical conversion film, the higher the washing effect. When the
temperature of water in the water washing step exceeds 90.degree.
C., it may cause increase in energy cost, and the aluminum alloy
base material may cause a hydration reaction with water and the
hydrated oxide film of aluminum may be formed on the surface of the
base material. Thus, it is preferable that at least the temperature
of water in the first water washing step after forming a chemical
conversion film be 30.degree. C. to 90.degree. C., it is more
preferable that it be 40.degree. C. to 85.degree. C., and it is
further preferable that it be 50.degree. C. to 85.degree. C. A
temperature of water in the water washing step after that may be
any as long as it is within a range of 10.degree. C. to 90.degree.
C. After the water washing step, it is desirable that drying by hot
blast and the like be performed to remove water droplets remained
on the surface of the aluminum alloy base material.
[0053] (Treating Method of Each Step)
[0054] For the degreasing step, performing acid etching, forming a
chemical conversion film, and the water washing step associated
with each step, a method of spraying the treatment liquid to the
surface of the aluminum alloy, a method of passing the aluminum
alloy through a treating vessel filled with the treatment liquid
(immersion method), or the like is preferably used.
[0055] (Method of Using Aluminum Alloy Material)
[0056] The aluminum alloy material of the present disclosure can be
used as a member for automobiles, construction machines, and
transportation machines by providing the adhesive layer on the
surface of the chemical conversion film and subsequently further
adhering to another aluminum alloy material. Since the aluminum
alloy material of the present disclosure is excellent in the
adhesion durability with another material, the aluminum alloy
material can strongly adhere to the other aluminum alloy material
via the adhesive, and can maintain the adhesion in a long term. As
the adhesive, an epoxy resin, an acrylic resin, a urethane resin,
and the like can be mentioned, and a thermosetting epoxy resin is
preferably used. A thickness of the adhesive layer provided on the
surface of the chemical conversion film is not particularly
limited, but it is preferable that it be 10 to 5000 .mu.m it is
more preferable that it be 20 to 3000 .mu.m, and it is further
preferable that it be 30 to 1000 .mu.m.
EXAMPLE
[0057] Hereinafter, the present disclosure will be described in
detail based on Examples. The present disclosure is not limited to
the examples described below, and the constitution can be
appropriately changed within a range not impairing the spirit of
the present disclosure.
Examples 1 to 8
[0058] Base materials with a size of 1 mm in plate thickness and 7
cm.times.15 cm, shown in the following Table 1, were prepared, and
acid etching was performed on the base materials under the
following conditions. In Examples 1 to 3, the acid etching was
performed for 6 seconds under conditions shown in Table 1 by using
an etching liquid at 60.degree. C. having a composition of 0.5 mass
% sulfuric acid +0.05 mass % hydrofluoric acid. Similarly, in
Examples 4 to 7, the acid etching was performed for 4 seconds under
conditions shown in Table 1 by using an etching liquid at
60.degree. C. having a composition of 0.5 mass % sulfuric acid
+0.05 mass % hydrofluoric acid. In Example 8, the acid etching was
performed for 4 seconds under conditions shown in Table 1 by using
an etching liquid at 80.degree. C. having a composition of 10 mass
% sulfuric acid. After the acid etching, the substrate was washed
with ion-exchanged water at a temperature of 70.degree. C. having
an electroconductivity at a temperature of 20.degree. C. of 0.2
mS/m. Next, chemical conversion treatment was immediately applied
under conditions of temperature, composition, and treating time
shown in Table 1 to obtain an aluminum alloy material having a base
material and a chemical conversion film with a film amount shown in
Table 1. A fluorinated titanium compound and a fluorinated
zirconium compound that were used in Examples 1 to 8 were
hexafluorotitanic acid and hexafluorozirconic acid, respectively.
After the chemical conversion treatment, the base material was
immediately washed with ion-exchanged water at 70.degree. C. having
an electroconductivity at a temperature of 20.degree. C. of 0.2
mS/m, further washed with ion-exchanged water at a room temperature
(specifically, 20.degree. C.) having an electroconductivity at a
temperature of 20.degree. C. of 0.1 mS/m, and then warm wind at
50.degree. C. was blown to dry the base material. The
electroconductivity of water was measured with "Portable
Conductivity Meter ES-71", manufactured by HORIBA, Ltd.
Comparative Examples 1 to 2
[0059] In Comparative Example 1, a base material with the size same
as that used in Example shown in Table 1 was prepared, acid etching
was performed on the base material for 4 seconds under conditions
shown in Table 1 by using an etching liquid at 80.degree. C. having
a composition of 10 mass % sulfuric acid, and the substrate was
washed with ion-exchanged water at a temperature of 70.degree. C.
having an electroconductivity at a temperature of 20.degree. C. of
0.2 mS/m to obtain an aluminum alloy base material. No chemical
conversion treatment was performed in Comparative Example 1. In
Comparative Example 2, acid etching was performed for 1 second
under conditions shown in Table 1 by using an etching liquid at
50.degree. C. having a composition of 10 mass % sulfuric acid,
after the acid etching, the substrate was washed with ion-exchanged
water at a temperature of 70.degree. C. having an
electroconductivity at a temperature of 20.degree. C. of 0.2 mS/m
and then chemical conversion treatment was immediately performed
under conditions shown in Table 1 to obtain an aluminum alloy
material having a base material and a chemical conversion film with
a film amount shown in Table 1. A fluorinated titanium compound and
a fluorinated zirconium compound that were used in Comparative
Example 2 were hexafluorotitanic acid and hexafluorozirconic acid,
respectively. After the chemical conversion treatment, the base
material was immediately washed with ion-exchanged water at
70.degree. C. having an electroconductivity at a temperature of
20.degree. C. of 0.2 mS/m, further washed with ion-exchanged water
at a room temperature (specifically, 20.degree. C.) having an
electroconductivity at a temperature of 20.degree. C. of 0.1 mS/m,
and then warm wind at 50.degree. C. was blown to dry the base
material.
TABLE-US-00001 TABLE 1 Example 1 5182 4.5 400 89 100 100 40 4 800
5.1 4.1 9.2 Example 2 5182 4.5 400 89 100 100 30 3 600 1.3 1.4 2.7
Example 3 5182 4.5 400 89 100 100 60 7 1400 17.2 11.9 29.1 Example
4 5182 4.5 250 56 100 100 40 1 200 2.5 5.0 7.5 Example 5 5182 4.5
250 56 100 100 40 7 1400 5.9 11.8 17.7 Example 6 5182 4.5 250 56 20
20 30 1.5 60 1.0 1.0 2.0 Example 7 5182 4.5 250 56 100 100 50 7
1400 13.0 14.0 27.0 Example 8 5182 2.5 150 60 100 100 50 3 600 5.0
5.0 10.0 Comparative 5182 4.5 150 33 -- -- -- -- -- -- -- --
Example 1 Comparative 5182 4.5 40 0 100 100 40 4 800 4.8 5.1 9.9
Example 2 indicates data missing or illegible when filed
[0060] A cathodic polarization curve of the aluminum alloy material
of each example obtained as above was measured with the above
method. FIG. 2 is a graph indicating a cathodic polarization curve
of the aluminum alloy material of Example 2 measured as above.
[0061] As an evaluation of adhesion, on the aluminum alloy material
obtained in each example, an evaluation was performed with a method
based on a modified APGE test described in Japanese National
Publication of International Patent Application No. 2018-527467 to
measure an adhesion-rupture cycle Cy. A detailed procedure of the
modified APGE test is as follows. Two sheets of materials to be
measured with 52.5 mm in length.times.25 mm in width were adhered
so that a length of an adhering part was 12.5 mm and an adhering
thickness was 0.2 mm by using an epoxy-based adhesive. To prevent
the material to be measured with 1 mm in plate thickness from
deforming during the test, a similar plate was adhered with a
similar adhesive in advance to be used. Thereafter, six pairs of
the materials to be measured produced in the above procedure were
bonded at each end portion with a stainless steel bolt. To prevent
galvanic corrosion due to a contact between the stainless steel
bolt and the material to be measured, the bat was insulated with an
appropriate method such as winding with a sealing tape. The six
pairs of the bonds were maintained in a state where a tensile
stress of 2400 N was persistently applied to both ends thereof.
Further, the bonds with the state of applying the stress were
immersed in a 5 mass % NaCl aqueous solution for 15 minutes, taken
out to the atmosphere at a room temperature of 25.degree. C. to be
naturally dried for 105 minutes, and put in a thermohygrostat
chamber set at 50.degree. C. and a relative humidity of 90% RH to
be maintained for 22 hours. According to this method, durability in
a highly strict deteriorative environment of the adhesion boundary
with both the tensile stress and the corrosive environment can be
evaluated. Furthermore, the procedure from applying the tensile
stress of 2400 N to finishing the maintenance in the
thermohygrostat chamber for 22 hours was counted as one cycle, and
one cycle of the test was performed in one weekday. In a holiday,
the bonds was kept being put in the thermohygrostat chamber for 48
hours, and not counted as the test cycle. The bonding state of the
sample was checked at a start of the next cycle, and when a break
was observed in any one pair of the bond in the six pairs of the
bonded specimens, the number of cycle at this time was specified as
a first break (break of a first pair). When a break of the material
to be measured was observed from applying the tensile stress of
2400 N to putting in the thermohygrostat chamber, the number of
cycle at this time was also specified as a first break. The broken
material to be measured was removed, a single plate having the size
same as one pair of the material to be measured was inserted to be
bonded to the other material to be measured with a bolt, and the
stress was applied again to restart the test cycle. When a
plurality of the bonding parts of the specimens were broken at the
same time, each of them was counted as the same number of cycle.
For example, when there is no break at the end of the 19th cycle
and two pairs in the six pairs of the specimens have been broken at
the start of 20th cycle, each of the first break and the second
break is specified as 20 cycles, and the next break is to be a
third break. This procedure was repeated, and the test was
continued until a fourth break (a time when any of four pairs in
the six pairs of the bonded specimens were broken). Thereafter, an
average value of numbers of cycle from the first break to the
fourth break was determined (rounded off the decimal place) to be
specified as Cy. A case where Cy<18 was evaluated as poor", a
case where 18.ltoreq.Cy<20 was evaluated as good", and a case
where 20.ltoreq.Cy was evaluated as "excellent". The above
measurement results are shown in Table 2.
TABLE-US-00002 TABLE 2 Polarization Potential at which cathode
current density reaches 10 .mu.A/cm.sup.2 Adhesion evaluation (mV
vs. 25.degree. C. (excellent, good, poor) saturated KCl Cy < 18:
Poor silver-silver 18 .ltoreq. Cy < 20: Good chloride electrode)
20 .ltoreq. Cy: Excellent Example 1 -1242 Excellent Example 2 -1201
Excellent Example 3 -1302 Good Example 4 -1230 Excellent Example 5
-1275 Excellent Example 6 -1150 Good Example 7 -1295 Excellent
Example 8 -1240 Excellent Comparative -1089 Poor Example 1
Comparative -1130 Poor Example 2
[0062] As seen from Table 2, in Examples 1 to 8, the adhesion
evaluations were "good" or "excellent", whereas in Comparative
Examples 1 to 2, the adhesion evaluations were "poor". From the
above, it is found that the excellent adhesion durability can be
Obtained in the aluminum alloy material of the present
disclosure.
* * * * *