GB/T 7998-2005 English PDF (GBT7998-2005)

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GB/T 7998-2005: Test method for intergranular corrosion of aluminium alloy
GB/T 7998-2005
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.30
H 25
GB 7998-2005
Replacing GB 7998-1987
Test method for intergranular corrosion of
aluminium alloy
ISSUED ON. JULY 4, 2005
IMPLEMENTED ON. DECEMBER 1, 2005
Jointly Issued by. General Administration of Quality Supervision,
Inspection and Quarantine of the People's Republic of
China;
Standardization Administration of the People's
Republic of China.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Method summary ... 4 
4 Reagents ... 4 
6 Sample ... 5 
7 Corrosion test of sample ... 6 
8 Metallographic examination ... 7 
9 Result expression ... 8 
10 Test report ... 8 
Foreword
This Standard is formulated by reference to ASTM G110-1992 “Standard Practice for
Evaluating Intergranular Corrosion Resistance of Heat Treatable Aluminum Alloys by
Immersion in Sodium Chloride + Hydrogen Peroxide Solution”.
This Standard replaces GB/T 7998-1987.
This Standard makes a lot of editorial changes to GB/T 7998-1987.
This Standard was proposed by China Nonferrous Metals Industry Association.
This Standard shall be under the jurisdiction of the National Non-ferrous Metals
Standardization Technical Committee.
This Standard is responsibly drafted by the Northeast Light Alloy Co., Ltd.
Main drafters of this Standard. Gao Zhenzhong, Hou Yi, Zheng Yunlong, Wang Meiqi,
and Sun Yanchang.
This Standard shall be responsibly interpreted by the National Standardization
Technical Committee of Non-ferrous Metals.
The historical version replaced by this Standard is as follows.
- GB/T 7998-1987.
Test method for intergranular corrosion of
aluminium alloy
1 Scope
This Standard specifies the test method for intergranular corrosion of aluminum alloy.
This Standard applies to intergranular corrosion’s inspection and measurement of
intergranular corrosion of series-2XXX alloy, series-7XXX alloy, and series-5XXX
alloy.
2 Method summary
This method uses metalloscope to perform the intergranular corrosion’s inspection to
the surface of samples or products that have not gone through corrosion, or to the
samples that are after corrosion test (in sodium chloride solution, add hydrogen
peroxide or hydrochloric acid; immerse the sample; conduct intergranular corrosion’s
accelerated corrosion test of reinforced cathode depolarization), and measure the
depth of intergranular corrosion.
3 Terms and definitions
3.1
intergranular corrosion
It refers to the corrosion phenomenon that is occurred along the metal grain boundary
or near the grain boundary.
3.2
cathode depolarization
Those, that can eliminate or reduce the polarization caused by the convergence of the
original battery blockade, are known as depolarization. The depolarization effect that
is corrosive to battery cathode polarization is called cathode depolarization.
Enhancing the cathode depolarization can accelerate the corrosion rate.
4 Reagents
the removed thickness is 2 times of the product nominal aluminium-cladded
layer-thickness. If there still remains aluminium-cladded layer, this sample is void, a
new sampling shall be conducted.
7.2 Preparing test solution
7.2.1 For series-2XXX and series-7XXX alloy samples, pipette sodium chloride
solution (4.5) into a container; according to per liter of solution containing 10 mL of
hydrogen peroxide (4.1), add hydrogen peroxide; mix well.
7.2.2 For series-5XXX alloy sample, pipette sodium chloride solution (4.6) into a
container; according to per liter of solution containing 10 mL of hydrochloric acid (4.2),
add hydrochloric acid; mix well.
7.3 Sample corrosion
7.3.1 test shall be conducted at constant temperature of 35°C ± 2°C. Test temperature
is controlled by a thermostat device.
7.3.2 The sample is hung with a plastic wire, and completely immersed in the test
solution that is newly prepared (7.2). The ratio of sample’s surface area to the test
solution’s volume is less than 20 mm2/mL. Different alloy samples can not be placed
in the same container; between the samples or between the sample and the container,
they can not touch each other.
7.3.3 For series-2XXX alloys and series-7XXX alloys, the test time is 6h; for
series-5XXX alloys, the test time is 24 h.
7.3.4 After corrosion, the sample is washed with water and dried.
8 Metallographic examination
8.1 After corrosion, the test sample is cut out (do not use shear-cut method) by 5mm
at one end along vertical main deformation direction. After cutting, the cross-section is
processed according to 8.2. The sample that is not gone through corrosion test shall
be directly processed according to 8.2.
8.2 According to metallographic sample preparation method, grind and polish (prevent
chamfer) the sample; without immersion-corrosion, observe by optical metalloscope
(magnification 100X – 500X). If net-shaped grain boundary appears, then it is deemed
as intergranular corrosion (typical intergranular corrosion photograph is shown in
Figure 2); measure its maximum depth of intergranular corrosion.
c) Alloy designation or chemical composition;
d) Processing status;
e) The sample is with or without aluminium-cladded;
f) If test results have intergranular corrosion, indicate.
1) The distribution of intergranular corrosion;
2) The maximum depth of intergranular corrosion (or grade);
3) When necessary, photo shall be attached for illustration.
g) Other test results that may affect the situation or that are required to be
indicated.