ASTM B457-67(2003)

Standard Test Method for Measurement of Impedance of Anodic Coatings on Aluminum

SCOPE
1.1 This test method describes the conditions and equipment for measuring the impedance of anodic coatings on aluminum. Such measurements have been used to evaluate the quality of seal of an anodic coating. The test method does not prescribe the procedure for producing the anodic coating, nor the postanodizing treatment usually described as "sealing."
1.2 This test method is applicable to the rapid, nondestructive testing of anodic coatings. The interpretation of results and correlation of data with service experience and other tests are not within the scope of this test method.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 09-Nov-1998
• ICS: 25.220.20 - Surface treatment
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.07 - Conversion Coatings

Relations

• Replaces: ASTM B457-67(1998) - Standard Test Method for Measurement of Impedance of Anodic Coatings on Aluminum
• Effective Date: 10-Nov-1998
• Replaced By: ASTM B457-67(2008)e1 - Standard Test Method for Measurement of Impedance of Anodic Coatings on Aluminum
• Effective Date: 01-Apr-2008
• Referred By: ASTM B580-79(2019) - Standard Specification for Anodic Oxide Coatings on Aluminum
• Effective Date: 10-Nov-1998

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:B457–67 (Reapproved 2003)
Standard Test Method for
Measurement of Impedance of Anodic Coatings on
Aluminum
This standard is issued under the fixed designation B 457; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
R 2 r ~l/A!
1. Scope
(3)
1.1 Thistestmethoddescribestheconditionsandequipment
for measuring the impedance of anodic coatings on aluminum.
where:
Such measurements have been used to evaluate the quality of
R = resistance,
seal of an anodic coating. The test method does not prescribe
r = specific resistance,
the procedure for producing the anodic coating, nor the l = length of conductor, and
A = area of cross section of conductor.
postanodizing treatment usually described as “sealing.”
1.2 This test method is applicable to the rapid, nondestruc-
C 5 e~A/l!
tive testing of anodic coatings.The interpretation of results and
(4)
correlation of data with service experience and other tests are
where:
not within the scope of this test method.
C = capacitance,
1.3 This standard does not purport to address all of the
e = dielectric constant,
safety concerns, if any, associated with its use. It is the
A = area of opposing plates of capacitor, and
responsibility of the user of this standard to establish appro-
l = distance between plates.
priate safety and health practices and determine the applica-
2.3 For measuring impedance of anodic coatings, the mate-
bility of regulatory limitations prior to use.
rial constants are partly associated with the anodic coating and
partly with the electrolyte employed in the test cell. For
2. Nature of Test
simplification these constants are assumed not to vary. The
2.1 Impedanceisanelectricalcharacteristicdescribedasthe
variations in measured impedance then depend directly on
total opposition of all circuit elements to the flow of alternating
geometric factors.
current. Inductive effects of anodic coatings are negligible and
the impedance is presumed to be made up of resistance and
3. Apparatus
capacitive reactance according to the following relationships:
3.1 Impedance Bridges—Commercially available a-c im-
2 2
Z 5 =R 1 X (1)
pedance bridges with the following characteristics are satisfac-
c
tory:
and
3.1.1 Range—1 µF (1000 nF) to 0.0001 µF (0.1 nF) full
X 5 1/2 pfC (2)
c
scale with a dissipation factor of 0 to 2.
3.1.2 Frequency—1000 Hz.
where:
3.1.3 Accuracy—1 %.
Z = impedance,
3.1.4 Voltage—Adjustable so as to be not greater than 0.5 V
R = resistance,
X = capacitive reactance,
as applied to the test specimen.
c
f = frequency, and
C = capacitance.
2.2 Both resistance and capacitance are associated with a
material constant and a geometric factor:
TheAlcoaImpedanceTestforAnodicCoatings(AZTAC)evaluatesa0.129-cm
2 (0.02-in. ) test area and expresses impedance in kilohms. Instructions are available
from Alcoa Process Development Laboratories, P.O. Box 2970, Pittsburgh, PA
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic 15230.
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on The Z-Scope, formerly manufactured by Twin City Testing Corp., Tonawanda,
Chromate Conversion Coatings. NY was designed to measure the impedance of anodic coatings on aluminum.
2 2
Current edition approved Feb. 10, 2003. Published May 2003. Originally AZTAC values (the impedance of a 0.129-cm (0.02-in. ) test area) can be read
approved in 1967. Last previous edition approved in 1998 as B 457 – 67 (1998). directly in kilohms with this instrument.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B457–67 (2003)
of the solution from the probe, and free from mechanical
defects such as scratches. After an anodic coating has been
sealed, moisture is lost from the coating thus producing an
increase in impedance. The rate at which moisture is lost
increases as the relative humidity decreases; therefore, the
relative humidity of the testing environment should be con-
trolled and never below 25 %. Specimens should be tested
within 1 h after the anodic coating has been sealed. If this
cannot be done or if the part has been subjected to an elevated
temperature drying treatment, the test area should be condi-
tioned as follows:
5.1.1 Wipe the test area with acetone, methylethylketone,
trichloroethylene, or similar solvent.
5.1.2 Immerse the test area in pure boiling water for 30 s.
5.1.3 Rinse in cold water.
5.1.4 Blot dry and test without further delay.
6. Procedure
6.1 Penetrate the anodic coating in a small area with a sharp
instrument and connect the lead from the low-impedance
terminal of the bridge to the exposed aluminum substrate.
FIG. 1 Diagram of Test Cell Construction
6.2 Connect the other lead from the bridge to the counter
electrode of the test cell. Be certain the lead wires are not
3.2 Cell (Fig. 1) for containing the electrolyte during test. It
twisted around each other. Turn on the bridge and allow it to
may be constructed from the following components:
warm up.
3.2.1 Glass Tube, 9 mm (0.35 in.) in outside diameter by 9
6.3 Place the test cell on the area to be tested and apply
cm (3.54 in.).
enough pressure, 490 to 1230 MPa (71 to 178 psi) to prevent
3.2.2 Rubber Gasket or Seal.
leakage of the electrolyte (the cell is spring-loaded to ensure
3.2.3 Rubber Stopper—Any convenient size with a hole in
sufficient and constant pressure). Make certain the bottom of
center to accommodate the glass tube.
the gasket on the test cell is level with the test surface.
3.2.4 Platinum or Type 300 Stainless Steel Counter Elec-
6.4 Fill the test cell at least half full with electrolyte and
trode, 9 cm (3.54 in.) long by 0.75 to 1.0 mm (0.030 to 0.040
commence a 2-min soak period. The counter electrode should
in.) diameter wir
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