ASTM B766-86(1998)
(Specification)Standard Specification for Electrodeposited Coatings of Cadmium
Standard Specification for Electrodeposited Coatings of Cadmium
SCOPE
1.1 This specification covers the requirements for electrodeposited cadmium coatings on products of iron, steel, and other metals. Note 1-Cadmium is deposited as a coating principally on iron and steel products. It can also be electrodeposited on aluminum, brass, beryllium copper, copper, nickel, and powder metallurgy parts.
1.2 The coating is provided in various thicknesses up to and including 25 [mu]m either as electrodeposited or with supplementary finishes.
1.3 Cadmium coatings are used for corrosion resistance and for corrosion prevention of the basis metal part. The as-deposited coating (Type I) is useful for the lowest cost protection in a mild or noncorrosive environment where early formation of white corrosion products is not detrimental or harmful to the function of a component. The prime purpose of the supplementary chromate finishes (Types II and III) on the electroplated cadmium is to increase corrosion resistance. Chromating will retard or prevent the formation of white corrosion products on surfaces exposed to various environmental conditions as well as delay the appearance of corrosion from the basis metal.
1.4 Cadmium plating is used to minimize bi-metallic corrosion between high-strength steel fasteners and aluminum in the aerospace industry. Undercutting of threads on fastener parts is not necessary as the cadmium coating has a low coefficient of friction that reduces the tightening torque required and allows repetitive dismantling.
1.5 Cadmium-coated parts can easily be soldered without the use of corrosive fluxes. Cadmium-coated steel parts have a lower electrical contact resistance than zinc-coated steel. The lubricity of cadmium plating is used on springs for doors and latches and for weaving machinery operating in high humidity. Corrosion products formed on cadmium are tightly adherent. Unlike zinc, cadmium does not build up voluminous corrosion products on the surface. This allows for proper functioning during corrosive exposure of moving parts, threaded assemblies, valves, and delicate mechanisms without jamming with debris.
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Standards Content (Sample)
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Designation: B 766 – 86 (Reapproved 1998)
Standard Specification for
Electrodeposited Coatings of Cadmium
This standard is issued under the fixed designation B 766; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope blies, valves, and delicate mechanisms without jamming with
debris.
1.1 This specification covers the requirements for electrode-
posited cadmium coatings on products of iron, steel, and other
2. Referenced Documents
metals.
2.1 The following standards form a part of this document to
NOTE 1—Cadmium is deposited as a coating principally on iron and
the extent referenced herein.
steel products. It can also be electrodeposited on aluminum, brass,
2.2 ASTM Standards:
beryllium copper, copper, nickel, and powder metallurgy parts.
A 165 Specification for Electrodeposited Coatings of Cad-
1.2 The coating is provided in various thicknesses up to and
mium on Steel
including 25 μm either as electrodeposited or with supplemen-
B 117 Practice for Operating Salt Spray (Fog) Apparatus
tary finishes.
B 183 Practice for Preparation of Low-Carbon Steel for
1.3 Cadmium coatings are used for corrosion resistance and
Electroplating
for corrosion prevention of the basis metal part. The as-
B 201 Practice for Testing Chromate Coatings on Zinc and
deposited coating (Type I) is useful for the lowest cost
Cadmium Surfaces
protection in a mild or noncorrosive environment where early
B 242 Practice for Preparation of High-Carbon Steel for
formation of white corrosion products is not detrimental or
Electroplating
harmful to the function of a component. The prime purpose of
B 253 Guide for Preparation of Aluminum Alloys for Elec-
the supplementary chromate finishes (Types II and III) on the
troplating
electroplated cadmium is to increase corrosion resistance.
B 254 Practice for Preparation of and Electroplating on
Chromating will retard or prevent the formation of white
Stainless Steel
corrosion products on surfaces exposed to various environmen-
B 281 Practice for Preparation of Copper and Copper-Base
tal conditions as well as delay the appearance of corrosion from
Alloys for Electroplating and Conversion Coatings
the basis metal.
B 320 Practice for Preparation of Iron Castings for Electro-
1.4 Cadmium plating is used to minimize bi-metallic corro-
plating
sion between high-strength steel fasteners and aluminum in the
B 322 Practice for Cleaning Metals Prior to Electroplating
aerospace industry. Undercutting of threads on fastener parts is
B 343 Practice for Preparation of Nickel for Electroplating
not necessary as the cadmium coating has a low coefficient of
with Nickel
friction that reduces the tightening torque required and allows
B 374 Terminology Relating to Electroplating
repetitive dismantling.
B 487 Test Method for Measurement of Metal and Oxide
1.5 Cadmium-coated parts can easily be soldered without
Coating Thicknesses by Microscopical Examination of a
the use of corrosive fluxes. Cadmium-coated steel parts have a
Cross Section
lower electrical contact resistance than zinc-coated steel. The
B 499 Test Method for Measurement of Coating Thick-
lubricity of cadmium plating is used on springs for doors and
nesses by the Magnetic Method: Nonmagnetic Coatings on
latches and for weaving machinery operating in high humidity.
Magnetic Basis Metals
Corrosion products formed on cadmium are tightly adherent.
B 504 Test Method for Measurement of Thickness of Me-
Unlike zinc, cadmium does not build up voluminous corrosion
tallic Coatings by the Coulometric Method
products on the surface. This allows for proper functioning
B 507 Practice for Design of Articles to Be Electroplated on
during corrosive exposure of moving parts, threaded assem-
Racks
1 2
This specification is under the jurisdiction of ASTM Committee B-8 on Discontinued; see 1987 Annual Book of ASTM Standards, Vol 02.05. Replaced
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee by Specification B 766.
B08.08.04on Light Metals. Annual Book of ASTM Standards, Vol 03.02.
Current edition approved Sept. 26, 1986. Published November 1986. Annual Book of ASTM Standards, Vol 02.05.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information. Contact ASTM International (www.astm.org) for the latest information.
B 766
B 558 Practice for Preparation of Nickel Alloys for Electro- mation to the seller in the purchase order or other governing
plating document:
B 567 Test Method for Measurement of Coating Thickness 5.1.1 The name, designation, and date of issue of this
by the Beta Backscatter Method specification.
B 568 Test Method for Measurement of Coating Thickness 5.1.2 Deposit by class and type (4.1 and 4.2).
by X-Ray Spectrometry 5.1.3 Composition and metallurgical condition of the sub-
B 571 Test Methods for Adhesion of Metallic Coatings strate to be coated. Application to high-strength steel parts
B 602 Test Method for Attribute Sampling of Metallic and (6.2).
Inorganic Coatings 5.1.4 Heat treatment for stress relief, whether it has been
B 697 Guide for Selection of Sampling Plans for Inspection performed or is required (6.3).
of Electrodeposited Metallic and Inorganic Coatings 5.1.5 Additional undercoat, if required (6.5).
E 8 Test Methods for Tension Testing of Metallic Materials 5.1.6 Plating process variation, if required (6.6).
F 519 Method for Mechanical Hydrogen Embrittlement 5.1.7 Hydrogen embrittlement relief, if required (6.7).
Testing of Plating Processes and Aircraft Maintenance 5.1.8 Desired color of the Type II film (6.8.2).
Chemicals 5.1.9 Location of significant surfaces (7.1.2).
2.3 Federal Standard: 5.1.10 Coating luster (7.5).
QQ-P-416 Plating, Cadmium (Electrodeposited) 5.1.11 Whether non-destructive or destructive tests are to be
2.4 International Standard: used in cases of choice (Note 14).
ISO 2082 Metallic Coatings—Electroplated Coatings of 5.1.12 Configuration, procedures, and tensile load for hy-
Cadmium on Iron or Steel drogen embrittlement relief test (9.4, 10.6, Supplementary
2.5 Military Standard: Requirements S2, and S3).
MIL-STD-1312 Fasteners, Test Methods 5.1.13 Whether certification is required (Section 12).
5.1.14 Whether supplementary requirements are applicable.
3. Terminology
3.1 Definitions—Definitions of terms used in this specifica-
6. Materials and Manufacture
tion are in accordance with Terminology B 374.
6.1 Nature of Coating—The coating shall be essentially
4. Classification
pure cadmium produced by electrodeposition usually from an
alkaline cyanide solution.
4.1 Classes—Electrodeposited cadmium coatings shall be
6.2 High Tensile Strength Steel Parts— Steel parts having
classified on the basis of thickness as follows:
an ultimate tensile strength greater than 1650 MPa (approxi-
Class Minimum Thickness, μm
mately 50 HRC) shall not be plated by electrodeposition unless
25 25
authorized by the purchaser.
12 12
6.3 Stress Relief—Steel parts having an ultimate tensile
strength of 1050 MPa (approximately 35 HRC) and above, and
that have been machined, ground, cold-formed, or cold-
NOTE 2—Cadmium coatings thicker than 12 μm are normally not
straightened shall be heat-treated at 190 6 15°C for5hor
economical.
more for stress relief before cleaning and coating.
4.2 Types—Electrodeposited cadmium coatings shall be
6.4 Preparatory Procedures—The basis metal shall be sub-
identified by types on the basis of supplementary treatment
jected to such cleaning procedures as necessary to ensure a
required as follows:
surface satisfactory for subsequent electroplating. Materials
4.2.1 Type I—As electrodeposited without supplementary
used for cleaning shall have no damaging effects on the basis
treatment.
metal resulting in pits, intergranular attack, stress corrosion
4.2.2 Type II—With supplementary colored chromate treat-
cracking, or hydrogen embrittlement. If necessary, cleaning
ment.
materials for steel parts should be evaluated in accordance with
4.2.3 Type III—With supplementary colorless chromate
Method F 519.
treatment.
NOTE 4—For basis metal preparation, the following standards should be
NOTE 3—It is strongly recommended that production items be pro-
employed depending upon the metallurgical composition: Practices B 183,
cessed as either Type II or Type III.
B 242, B 253, B 254, B 281, B 320, B 322, B 343 and B 558.
5. Ordering Information
6.5 Substrate—Cadmium shall be deposited directly on the
basis metal part without an undercoat of another metal except
5.1 In order to make the application of this specification
when the part is either stainless steel or aluminum and its
complete, the purchaser needs to supply the following infor-
alloys. An undercoat of nickel is permissible on stainless steel.
With aluminum and aluminum alloys, the oxide layer shall be
Annual Book of ASTM Standards, Vol 03.01.
removed and replaced by a metallic zinc layer in accordance
Annual Book of ASTM Standards, Vol 15.03.
Available from U.S. Government Printing Office, Washington DC 20402.
with Guide B 253. For better adherence, a copper strike or a
Available from American National Standards Institute, 11 W. 42nd St., 13th
nickel coating may be applied to the zinc layer before
Floor, New York, NY 10036.
9 electroplating with the cadmium.
Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS. 6.6 Plating Process—The plating shall be applied after all
NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information. Contact ASTM International (www.astm.org) for the latest information.
B 766
basis metal heat treatments and mechanical operations, such as serviceability of the article when assembled in normal position;
machining, brazing, welding, forming, and perforating of the or that can be the source of corrosion products that will deface
article, have been completed. visible surfaces on the assembled article. When necessary, the
6.7 Hydrogen Embrittlement Relief— Steel parts having a significant surfaces shall be indicated by the purchaser on
tensile strength of 1200 MPa (approximately 38 HRC) and applicable drawing of the article, or by the provision of
higher shall be baked at 190 6 15°C for8hor more within 4 suitably marked samples.
h after electroplating to provide hydrogen embrittlement relief.
NOTE 7—As heavier coatings are required for satisfactory corrosion
Electroplated springs and other parts subject to flexure shall not
resistance than Class 5, allowance should be made in the fabrication of
be flexed, loaded, or used before the hydrogen embrittlement
most threaded articles, such as nuts, bolts, and similar fasteners with
relief treatment. The baking treatment for hydrogen embrittle-
complementary threads for dimensional tolerances to obtain necessary
coating build-up. Flat surfaces and certain shielded or recessed areas, such
ment relief shall be done before the application of any
as root-diameter of threads, have a tendency to exhibit lack of build-up
supplementary chromate treatment. When specified, freedom
and to be heavier at exposed edges and sharp projections with electrode-
from embrittlement shall be determined.
posited coatings. This trend is also found with vacuum-deposited cad-
NOTE 5—For high-strength steels, greater than 1300 MPa or approxi- mium coatings and is in direct contrast with mechanically deposited
mately 40 HRC, it is strongly recommended that the baking time be coatings.
extended to 23 h or more to ensure hydrogen embrittlement relief.
NOTE 8—The coating thickness requirements of this specification is a
NOTE 6—Electroplated steel parts, passivated by the baking operation
minimum requirement. Variation in thickness from point to point on an
for hydrogen embrittlement relief, require reactivation before the chro-
article is inherent in electroplating. Therefore, the thickness will have to
mate treatment. This application, immersion in a dilute acid solution,
exceed the specified value at some points on the significant surfaces to
should be done as soon as practical. If the chromating solution contains
ensure that it equals or exceeds the specified value at all points. Hence, in
sulfuric acid, then the reactivating solution should be 1 part of sulfuric
most cases, the average coating thickness of an article will be greater than
acid (sp gr 1.83) by volume added to 99 parts of water. If the chromating
the specified value; how much greater is largely determined by the shape
solution contains hydrochloric acid, then the reactivating solution should
of the article (see Practice B 507) and the characteristics of the electro-
be 1 part of hydrochloric acid (sp gr 1.16) by volume added to 99 parts of
plating process. In addition, the average coating thickness on articles will
water. Duration of immersion should be as brief as is consistent with the
vary from article to article within a production lot. Therefore, if all of the
nature of the work. Separately racked items can be reactivated in
articles in a production lot are to meet the thickness requirement, the
approximately 5 s, whereas a perforated container of barrel-plated parts
average coating thickness for the production lot as a whole will be greater
requires approximately 15 s.
than the average necessary to assure that a single article meets the
requirement.
6.8 Chromate Treatment:
6.8.1 Chromate treatments for Types II and III shall be done
7.1.3 For nonsignificant visible surfaces, the minimum
in or with special aqueous acidic solutions composed of
thickness for Classes 25 and 12 shall be Class 8 (8 μm); for
hexavalent chromium along with certain anions that act as
Class 8 it shall be Class 5 (5 μm); and for Class 5 it shall be 4
catalyst or fi
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