ASTM B766-23

Standard Specification for Electrodeposited Coatings of Cadmium

ABSTRACT
This specification covers the requirements for electrodeposited cadmium coatings on products of iron, steel, and other metals. 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.Electrodeposited cadmium coatings shall be classified on the basis of thickness as Class 25, 12, 8, and 5. The coating shall be essentially pure cadmium produced by electrodeposition usually from an alkaline cyanide solution. The basis metal shall be subjected to such cleaning procedures as necessary to ensure a surface satisfactory for subsequent electroplating. Cadmium shall be deposited directly on the basis metal part without an undercoat of another metal except when the part is either stainless steel or aluminum and its alloys. The plating shall be applied after all basis metal heat treatments and mechanical operations. The thickness of the coating everywhere on the significant surface shall conform to the requirements of the specified class. The cadmium coating shall be sufficiently adherent to the basis metal to pass the tests. The supplementary Type II chromate film shall be adherent, nonpowdery, and abrasion resistant. The thickness of electrodeposited cadmium coatings shall be determined by the applicable test methods.
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 μm 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.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and R...

General Information

• Status: Published
• Publication Date: 30-Apr-2023
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.06 - Soft Metals

Relations

• Refers: ASTM F519-23 - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Dec-2023
• Refers: ASTM B571-23 - Standard Practice for Qualitative Adhesion Testing of Metallic Coatings
• Effective Date: 01-Nov-2023
• Refers: ASTM B849-02(2023) - Standard Specification for Pre-Treatments of Iron or Steel for Reducing Risk of Hydrogen Embrittlement
• Effective Date: 01-Nov-2023
• Refers: ASTM B201-80(2019) - Standard Practice for Testing Chromate Coatings on Zinc and Cadmium Surfaces
• Effective Date: 01-Apr-2019
• Refers: ASTM B849-02(2019) - Standard Specification for Pre-Treatments of Iron or Steel for Reducing Risk of Hydrogen Embrittlement
• Effective Date: 01-Apr-2019
• Refers: ASTM B281-88(2019)e1 - Standard Practice for Preparation of Copper and Copper-Base Alloys for Electroplating and Conversion Coatings
• Effective Date: 01-Apr-2019
• Refers: ASTM B558-79(2019) - Standard Practice for Preparation of Nickel Alloys for Electroplating
• Effective Date: 01-Apr-2019
• Refers: ASTM B320-60(2019) - Standard Practice for Preparation of Iron Castings for Electroplating
• Effective Date: 01-Apr-2019
• Refers: ASTM F519-18 - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Nov-2018
• Refers: ASTM B571-18 - Standard Practice for Qualitative Adhesion Testing of Metallic Coatings
• Effective Date: 01-Aug-2018
• Refers: ASTM F519-17a - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Dec-2017
• Refers: ASTM F519-17 - Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
• Effective Date: 01-Mar-2017
• Refers: ASTM B183-79(2014) - Standard Practice for Preparation of Low-Carbon Steel for Electroplating
• Effective Date: 01-Nov-2014
• Refers: ASTM B242-99(2014) - Standard Guide for Preparation of High-Carbon Steel for Electroplating
• Effective Date: 01-Nov-2014
• Refers: ASTM B201-80(2014) - Standard Practice for Testing Chromate Coatings on Zinc and Cadmium Surfaces
• Effective Date: 01-Nov-2014

Overview

ASTM B766-23: Standard Specification for Electrodeposited Coatings of Cadmium establishes comprehensive requirements for cadmium coatings applied to iron, steel, and various other metal products via electrodeposition. Cadmium coatings serve as a critical means of corrosion protection, delivering reliable performance in both mild and more aggressive environments. The standard outlines coating classes by thickness and designates types based on optional chromate treatment, ensuring optimized corrosion resistance and functional properties for diverse industrial needs.

Key Topics

• Scope: Covers electrodeposited cadmium coatings up to 25 μm in thickness for iron, steel, aluminum, brass, copper, nickel, and beryllium copper substrates.
• Coating Types:
  • Type I: As-deposited, for cost-effective protection in mild environments.
  • Type II: Supplementary colored chromate finish for increased corrosion resistance.
  • Type III: Supplementary colorless chromate finish, also for enhanced corrosion defense.
• Classes (by Coating Thickness):
  • Class 25 (25 μm)
  • Class 12 (12 μm)
  • Class 8 (8 μm)
  • Class 5 (5 μm)
• Corrosion Resistance: Supplementary chromate films significantly increase the time-to-failure in salt spray tests, ensuring longer service life.
• Preparation and Application: The substrate must be properly cleaned and pretreated to promote adhesion and minimize risks such as hydrogen embrittlement. For high-tensile steel, specified pre-baking and post-plating heat treatments are critical.
• Quality and Inspection: Includes detailed sampling procedures, coating thickness measurement methods, and acceptance criteria to ensure compliance and consistent product performance.

Applications

• Corrosion Protection: Widely utilized in industries where corrosion prevention of iron, steel, and other metals is critical, particularly where atmospheric or marine exposure is expected.
• Aerospace: Cadmium coating is essential for components such as high-strength steel fasteners mated with aluminum, reducing the risk of galvanic (bi-metallic) corrosion.
• Electronics: The coatings provide low electrical contact resistance, improved solderability without corrosive fluxes, and surface conductivity for sensitive equipment.
• Mechanical Components: Used for springs, latches, valves, and threaded assemblies due to cadmium's lubricity and the formation of tightly-adherent corrosion products that do not jam moving parts.
• Manufacturing Flexibility: The low coefficient of friction allows reduced tightening torque on fasteners and supports repetitive disassembly.
• Performance Under Stress: Type II and III chromate finishes allow components to withstand harsh conditions such as high humidity and condensation cycles, delaying both white corrosion of cadmium and rust of the base metal.

Related Standards

• ASTM B117: Salt Spray (Fog) Apparatus Practice - for corrosion resistance testing.
• ASTM B183, B242, B253, B254, B281, B320, B322: Methods and guides for substrate preparation and cleaning prior to electroplating.
• ASTM B487, B499, B504, B567, B568: Test methods for measuring metallic coating thickness.
• ASTM B571: Practice for Qualitative Adhesion Testing.
• ASTM B849, B850: Procedures to reduce and evaluate the risk of hydrogen embrittlement in plated steel.
• ISO 2082: International standard for electroplated cadmium coatings on iron and steel.
• Federal QQ-P-416: Specification for electrodeposited cadmium plating.
• MIL-STD-1312: Fasteners test methods, relevant for embrittlement testing and validation.

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ASTM B766-23 provides a robust framework for specifying, applying, and verifying electrodeposited cadmium coatings, meeting the rigorous requirements of industries where corrosion resistance, reliability, and mechanical performance are paramount. Proper adherence to this standard ensures product longevity, safety, and compliance with international best practices in metal finishing and protection.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B766 − 23
Standard Specification for
Electrodeposited Coatings of Cadmium
This standard is issued under the fixed designation B766; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope products on the surface. This allows for proper functioning
during corrosive exposure of moving parts, threaded
1.1 This specification covers the requirements for electrode-
assemblies, valves, and delicate mechanisms without jamming
posited cadmium coatings on products of iron, steel, and other
with debris.
metals.
1.6 This international standard was developed in accor-
NOTE 1—Cadmium is deposited as a coating principally on iron and
dance with internationally recognized principles on standard-
steel products. It can also be electrodeposited on aluminum, brass,
ization established in the Decision on Principles for the
beryllium copper, copper, nickel, and powder metallurgy parts.
Development of International Standards, Guides and Recom-
1.2 The coating is provided in various thicknesses up to and
mendations issued by the World Trade Organization Technical
including 25 μm either as electrodeposited or with supplemen-
Barriers to Trade (TBT) Committee.
tary finishes.
2. Referenced Documents
1.3 Cadmium coatings are used for corrosion resistance and
for corrosion prevention of the basis metal part. The as-
2.1 The following standards form a part of this document to
deposited coating (Type I) is useful for the lowest cost
the extent referenced herein.
protection in a mild or noncorrosive environment where early
2.2 ASTM Standards:
formation of white corrosion products is not detrimental or
A165 Specification for Electrodeposited Coatings of Cad-
harmful to the function of a component. The prime purpose of
mium on Steel (Withdrawn 1987)
the supplementary chromate finishes (Types II and III) on the
B117 Practice for Operating Salt Spray (Fog) Apparatus
electroplated cadmium is to increase corrosion resistance.
B183 Practice for Preparation of Low-Carbon Steel for
Chromating will retard or prevent the formation of white
Electroplating
corrosion products on surfaces exposed to various environmen-
B201 Practice for Testing Chromate Coatings on Zinc and
tal conditions as well as delay the appearance of corrosion from
Cadmium Surfaces
the basis metal.
B242 Guide for Preparation of High-Carbon Steel for Elec-
1.4 Cadmium plating is used to minimize bi-metallic corro-
troplating
sion between high-strength steel fasteners and aluminum in the
B253 Guide for Preparation of Aluminum Alloys for Elec-
aerospace industry. Undercutting of threads on fastener parts is
troplating
not necessary as the cadmium coating has a low coefficient of
B254 Practice for Preparation of and Electroplating on
friction that reduces the tightening torque required and allows
Stainless Steel
repetitive dismantling.
B281 Practice for Preparation of Copper and Copper-Base
1.5 Cadmium-coated parts can easily be soldered without Alloys for Electroplating and Conversion Coatings
B320 Practice for Preparation of Iron Castings for Electro-
the use of corrosive fluxes. Cadmium-coated steel parts have a
lower electrical contact resistance than zinc-coated steel. The plating
B322 Guide for Cleaning Metals Prior to Electroplating
lubricity of cadmium plating is used on springs for doors and
B343 Practice for Preparation of Nickel for Electroplating
latches and for weaving machinery operating in high humidity.
with Nickel
Corrosion products formed on cadmium are tightly adherent.
B374 Terminology Relating to Electroplating
Unlike zinc, cadmium does not build up voluminous corrosion
1 2
This specification is under the jurisdiction of ASTM Committee B08 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
B08.06 on Soft Metals. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved May 1, 2023. Published May 2023. Originally the ASTM website.
approved in 1986. Last previous edition approved in 2015 as B766 – 86 (2015). The last approved version of this historical standard is referenced on
DOI: 10.1520/B0766-23. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B766 − 23
B487 Test Method for Measurement of Metal and Oxide 4.2 Types—Electrodeposited cadmium coatings shall be
Coating Thickness by Microscopical Examination of identified by types on the basis of supplementary treatment
Cross Section required as follows:
B499 Test Method for Measurement of Coating Thicknesses 4.2.1 Type I—As electrodeposited without supplementary
by the Magnetic Method: Nonmagnetic Coatings on treatment.
Magnetic Basis Metals 4.2.2 Type II—With supplementary colored chromate treat-
B504 Test Method for Measurement of Thickness of Metal- ment.
lic Coatings by the Coulometric Method 4.2.3 Type III—With supplementary colorless chromate
B507 Practice for Design of Articles to Be Electroplated on treatment.
Racks
NOTE 3—It is strongly recommended that production items be pro-
B558 Practice for Preparation of Nickel Alloys for Electro-
cessed as either Type II or Type III.
plating
5. Ordering Information
B567 Test Method for Measurement of Coating Thickness
by the Beta Backscatter Method
5.1 In order to make the application of this specification
B568 Test Method for Measurement of Coating Thickness
complete, the purchaser needs to supply the following infor-
by X-Ray Spectrometry
mation to the seller in the purchase order or other governing
B571 Practice for Qualitative Adhesion Testing of Metallic
document:
Coatings
5.1.1 The name, designation, and date of issue of this
B602 Guide for Attribute Sampling of Metallic and Inor-
specification.
ganic Coatings
5.1.2 Deposit by class and type (4.1 and 4.2).
B697 Guide for Selection of Sampling Plans for Inspection
5.1.3 Composition, metallurgical condition, and tensile
of Electrodeposited Metallic and Inorganic Coatings
strength of the substrate to be coated. Application to high-
B849 Specification for Pre-Treatments of Iron or Steel for
strength steel parts (6.2), pretreatment (6.3) and post treatment
Reducing Risk of Hydrogen Embrittlement
(6.7).
B850 Guide for Post-Coating Treatments of Steel for Reduc-
5.1.4 Heat treatment for stress relief, whether it has been
ing the Risk of Hydrogen Embrittlement
performed or is required (6.3).
E8 Test Methods for Tension Testing of Metallic Materials
5.1.5 Additional undercoat, if required (6.5).
[Metric] E0008_E0008M
5.1.6 Plating process variation, if required (6.6).
F519 Test Method for Mechanical Hydrogen Embrittlement
5.1.7 Exception to stress relief heat treatment prior to
Evaluation of Plating/Coating Processes and Service En-
plating (6.3).
vironments
5.1.8 Baking requirements after plating, if any (6.7).
2.3 Federal Standard:
5.1.9 Desired color of the Type II film (6.8.2).
QQ-P-416 Plating, Cadmium (Electrodeposited)
5.1.10 Location of significant surfaces (7.1.2).
2.4 International Standard:
5.1.11 Coating luster (7.5).
ISO 2082 Metallic Coatings—Electroplated Coatings of
5.1.12 Whether non-destructive or destructive tests are to be
Cadmium on Iron or Steel
used in cases of choice (Note 14).
2.5 Military Standard: 5.1.13 Configuration, procedures, and tensile load for hy-
MIL-STD-1312 Fasteners, Test Methods
drogen embrittlement relief test (9.4, 10.6, Supplementary
Requirements S2, and S3).
3. Terminology
5.1.14 Whether certification is required (Section 12).
3.1 Definitions—Definitions of terms used in this specifica- 5.1.15 Whether supplementary requirements are applicable.
tion are in accordance with Terminology B374.
6. Materials and Manufacture
4. Classification
6.1 Nature of Coating—The coating shall be essentially pure
cadmium produced by electrodeposition usually from an alka-
4.1 Classes—Electrodeposited cadmium coatings shall be
line cyanide solution.
classified on the basis of thickness as follows:
Class Minimum Thickness, μm
6.2 High Tensile Strength Steel Parts—Steel parts having an
ultimate tensile strength greater than 1650 MPa (approximately
25 25
50 HRC) shall not be plated by electrodeposition unless
12 12
8 8
authorized by the purchaser.
5 5
6.3 Pretreatment of Iron or Steel for the Purpose of Reduc-
NOTE 2—Cadmium coatings thicker than 12 μm are normally not
ing the Risk of Hydrogen Embrittlement—Steel parts having an
economical.
ultimate tensile strength greater than 1000 MPa (31 HRC) that
contain tensile stresses caused by cold forming or cold straight-
Available from U.S. Government Printing Office, Washington DC 20402.
ening which have not been heat treated after the cold forming
Available from American National Standards Institute, 25 W. 43rd St., 4th
process, shall be heat treated for stress relief to reduce the risk
Floor, New York, NY 10036.
of hydrogen embrittlement in the part before clean and
Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS. electroplate processes. If these heat treatments are not required,
B766 − 23
acid (sp gr 1.83) by volume added to 99 parts of water. If the chromating
the purchaser shall specify in the ordering information their
solution contains hydrochloric acid, then the reactivating solution should
exception. If the purchaser does not specify an exception to
be 1 part of hydrochloric acid (sp gr 1.16) by volume added to 99 parts of
heat treatment, then the plater shall use Table 1 in Specification
water. Duration of immersion should be as brief as is consistent with the
B849 to determine the appropriate heat treatment for the steel
nature of the work. Separately racked items can be reactivated in
based on its tensile strength.
approximately 5 s, whereas a perforated container of barrel-plated parts
requires approximately 15 s.
6.4 Preparatory Procedures—The basis metal shall be sub-
6.8 Chromate Treatment:
jected to such cleaning procedures as necessary to ensure a
6.8.1 Chromate treatments for Types II and III shall be done
surface satisfactory for subsequent electroplating. Materials
in or with special aqueous acidic solutions composed of
used for cleaning shall have no damaging effects on the basis
hexavalent chromium along with certain anions that act as
metal resulting in pits, intergranular attack, stress corrosion
catalyst or film-forming compounds to produce a continuous
cracking, or hydrogen embrittlement. If necessary, cleaning
smooth protective film. Chromic acid and nitric acid bright
materials for steel parts should be evaluated in accordance with
dips shall not be used for treatment to produce chromate
Method F519.
coatings. When proprietary materials are used for this
NOTE 4—For basis metal preparation, the following standards should be
treatment, the instructions of the supplier should be followed.
employed depending upon the metallurgical composition: Practices B183,
6.8.2 The Type II film color shall range from an iridescent
B242, B253, B254, B281, B320, B322, B343, and B558.
yellow or a thicker, more protective iridescent bronze or brown
6.5 Substrate—Cadmium shall be deposited directly on the
to the heavier olive drab. It may also be dyed to a desired color.
basis metal part without an undercoat of another metal except
When necessary, the color of the film shall be indicated by the
when the part is either stainless steel or aluminum and its
purchaser and specified by the provision of a suitably colored
alloys. An undercoat of nickel is permissible on stainless steel.
sample or indicated on the drawing for the part.
With aluminum and aluminum alloys, the oxide layer shall be
6.8.3 The absence of color shall not be considered as
removed and replaced by a metallic zinc layer in accordance
evidence of lack of Type III film or as a basis for rejection.
with Guide B253. For better adherence, a copper strike or a
Presence of clear Type III film shall be determined by a spot
nickel coating may be applied to the zinc layer before
test as specified in 10.4.
electroplating with the cadmium.
6.8.4 Waxes, lacquers, or other organic coatings shall not be
6.6 Plating Process—The plating shall be applied after all used as a substitute for, nor may they be used in conjunction
basis metal heat treatments and mechanical operations, such as
with, supplementary treatments when the purpose is to ensure
machining, brazing, welding, forming, and perforating of the conformance to the salt spray requirements. Waxes and the
article, have been completed.
like, may be used to improve lubricity.
6.7 Hydrogen Embrittlement Relief—Electroplated steel
7. Coating Requirements
parts having a tensile strength greater than 1200 MPa
7.1 Thickness:
(39 HRC) as well as surface hardened parts, shall be baked to
7.1.1 The thickness of the coating everywhere on the
reduce the risk of hydrogen embrittlement. Baking of electro-
significant surfaces shall conform to the requirements of the
plated steel parts with tensile strength 1200 MPa (39 HRC) or
specified class, as defined in 4.1.
less is not mandatory.
7.1.2 Significant surfaces are those normally visible (di-
6.7.1 Steel parts having a tensile strength greater than
rectly or by reflection) that are essential to the appearance or
1200 MPa (39 HRC) as well as surface hardened parts, shall be
serviceability of the article when assembled in normal position;
baked to reduce the risk of hydrogen embrittlement. For such
or that can be the source of corrosion products that will deface
parts, purchasers shall specify the baking requirements in the
visible surfaces on the assembled article. When necessary, the
ordering information. Purchasers are directed to the appropri-
significant surfaces shall be indicated by the purchaser on
ate ER Class in Guide B850 Table 1.
applicable drawing of the article, or by the provision of
6.7.2 A purchaser wishing to specify baking requirements,
suitably marked samples.
irrespective of tensile strength, shall specify such requirements
in the ordering information. Purchasers are directed to Guide
NOTE 7—As heavier coatings are required for satisfactory corrosion
resistance than Class 5, allowance should be made in the fabrication of
B850 Table 1.
most threaded articles, such as nuts, bolts, and similar fasteners with
6.7.3 Any baking treatment done under this section shall
complementary threads for dimensional tolerances to obtain necessary
begin within 4 h of removal from the electroplating process.
coating build-up. Flat surfaces and certain shielded or recessed areas, such
6.7.4 Electroplated springs and other parts subject to flexure
as root-diameter of threads, have a tendency to exhibit lack of build-up
shall not be flexed before the hydrogen embrittlement relief and to be heavier at exposed edges and sharp projections with electrode-
posited coatings. This trend is also found with vacuum-deposited cad-
treatment.
mium coatings and is in direct contrast with mechanically deposited
NOTE 5—For high-strength steels, greater than 1300 MPa or approxi-
coatings.
mately 40 HRC, it is strongly recommended that the baking time be NOTE 8—The coating thickness requirements of this specification is a
extended to 23 h or more to ensure hydrogen embrittlement relief.
minimum requirement. Variation in thickness from point to point on an
NOTE 6—Electroplated steel parts, passivated by the baking operation article is inherent in electroplating. Therefore, the thickness will have to
for hydrogen embrittlement relief, require reactivation before the chro- exceed the specified value at some points on the significant surfaces to
mate treatment. This application, immersion in a dilute acid solution, ensure that it equals or exceeds the specified value at all points. Hence, in
should be done as soon as practical. If the chromating solution contains most cases, the average coating thickness of an article will be greater than
sulfuric acid, then the reactivating solution should be 1 part of sulfuric the specified value; how much greater is largely determined by the shape
B766 − 23
of the article (see Practice B507) and the characteristics of the electro-
deposit, such as excessively powdery or darkened coatings.
plating process. In addition, the average coating thickness on articles will
Superficial staining and variations in color or luster shall not be
vary from article to article within a production lot. Therefore, if all of the
cause for rejection. Defects and variations in appearance of the
articles in a production lot are to meet the thickness requirement, the
coating that arise from surface conditions of the substrate
average coating thickness for the production lot as a whole will be greater
(pores, scratches, roll marks, inclusions, and the like) and that
than the average necessary to assure that a single article meets the
requirement.
persist in the finish despite the observance of good application
techniques shall not be cause for rejection.
7.1.3 For nonsignificant visible surfaces, the minimum
thickness for Classes 25 and 12 shall be Class 8 (8 μm); for
NOTE 12—Coatings generally perform better in service when the
Class 8 it shall be Class 5 (5 μm); and for Class 5 it shall be 4
substrate over which they are applied is smooth and free from torn metal,
μm. inclusions, pores, and other defects. The specifications covering the
unfinished product should provide limits for these defects. A metal finisher
7.2 Adhesion—The cadmium coating shall be sufficiently
can often remove defects through special treatments such as grinding,
adherent to the basis metal to pass the tests detailed in 10.2. polishing, electropolishing, and chemical treatments. However these are
not normal in the treatment steps preceding the application of the coating.
7.3 Abrasion Resistant—The supplementary Type II chro-
When desired, they are subject of a special agreement between the
mate film shall be adherent, nonpowdery, and abrasion resistant
purchaser and supplier.
(10.3).
8. Sampling
7.4 Corrosion Resistance—Cadmium coatings with supple-
8.1 Inspection Lot—An inspection lot shall be a collection
mentary chromate films on iron and steel basis metals shall
of coated articles that are of the same kind, that have been
show neither white corrosion products of cadmium nor basis
produced to the same specifications, that have been coated by
metal corrosion products at the end of 96 h for Type II film or
a single supplier at one time or at approximately the same time
12 h for Type III film when tested by continuous exposure to
under essentially identical conditions, and that are submitted
salt spray. The appearance of corrosion products visible to the
for acceptance or rejection as a group.
unaided eye at normal reading distance shall be cause for
rejection, except white corrosion products at the edges of
8.2 Selection—A random sample of the size required by Test
specimens shall not constitute failure.
Method B602 shall be selected from the inspection lot. The
articles in the lot shall be inspected for conformance to the
NOTE 9—The hours given are the minimum required to guarantee
requirements of this specification and the lot shall be classified
satisfactory performance. Longer periods before the appearance of white
corrosion and basis metal corrosion (rust from iron and steel products) are as conforming to or nonconforming to each requirement in
possible. Salt spray resistance does not vary in exact proportion with
accordance with the criteria of the sampling plan in Test
increased plating thicknesses of Types II and III coatings. Although
Method B602.
specified hours to failure (red rust for iron and steel articles) for Type I
coating is not stated, the hours given for Types II and III reflect the added
NOTE 13—Test Method B602 contains four sampling plans, three of
protection of the chromate treatment without requiring impractical testing.
which are to be used with nondestructive test methods, the fourth is to be
NOTE 10—In many instances, there is no direct relation between the
used with destructive test methods. The three methods for nondestructive
results of an accelerated corrosion test and the resistance to corrosion in
tests differ in the quality level they require of the product. Test Method
other media. Factors such as the formation of protective films, basis
B602 requires u
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B766 − 86 (Reapproved 2015) B766 − 23
Standard Specification for
Electrodeposited Coatings of Cadmium
This standard is issued under the fixed designation B766; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. 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 μm 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.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 The following standards form a part of this document to the extent referenced herein.
This specification is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.06 on Soft
Metals.
Current edition approved March 1, 2015May 1, 2023. Published April 2015May 2023. Originally approved in 1986. Last previous edition approved in 20082015 as B766 –
86 (2008). DOI: 10.1520/B0766-86R15.(2015). DOI: 10.1520/B0766-23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B766 − 23
2.2 ASTM Standards:
A165 Specification for Electrodeposited Coatings of Cadmium on Steel (Withdrawn 1987)
B117 Practice for Operating Salt Spray (Fog) Apparatus
B183 Practice for Preparation of Low-Carbon Steel for Electroplating
B201 Practice for Testing Chromate Coatings on Zinc and Cadmium Surfaces
B242 Guide for Preparation of High-Carbon Steel for Electroplating
B253 Guide for Preparation of Aluminum Alloys for Electroplating
B254 Practice for Preparation of and Electroplating on Stainless Steel
B281 Practice for Preparation of Copper and Copper-Base Alloys for Electroplating and Conversion Coatings
B320 Practice for Preparation of Iron Castings for Electroplating
B322 Guide for Cleaning Metals Prior to Electroplating
B343 Practice for Preparation of Nickel for Electroplating with Nickel
B374 Terminology Relating to Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
B499 Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis
Metals
B504 Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
B507 Practice for Design of Articles to Be Electroplated on Racks
B558 Practice for Preparation of Nickel Alloys for Electroplating
B567 Test Method for Measurement of Coating Thickness by the Beta Backscatter Method
B568 Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
B571 Practice for Qualitative Adhesion Testing of Metallic Coatings
B602 Guide for Attribute Sampling of Metallic and Inorganic Coatings
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B849 Specification for Pre-Treatments of Iron or Steel for Reducing Risk of Hydrogen Embrittlement
B850 Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement
E8 Test Methods for Tension Testing of Metallic Materials [Metric] E0008_E0008M
F519 Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments
2.3 Federal Standard:
QQ-P-416 Plating, Cadmium (Electrodeposited)
2.4 International Standard:
ISO 2082 Metallic Coatings—Electroplated Coatings of Cadmium on Iron or Steel
2.5 Military Standard:
MIL-STD-1312 Fasteners, Test Methods
3. Terminology
3.1 Definitions—Definitions of terms used in this specification are in accordance with Terminology B374.
4. Classification
4.1 Classes—Electrodeposited cadmium coatings shall be classified on the basis of thickness as follows:
Class Minimum Thickness, μm
25 25
12 12
8 8
5 5
NOTE 2—Cadmium coatings thicker than 12 μm are normally not economical.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from U.S. Government Printing Office, Washington DC 20402.
Available from American National Standards Institute, 25 W. 43rd St., 4th Floor, New York, NY 10036.
Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
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4.2 Types—Electrodeposited cadmium coatings shall be identified by types on the basis of supplementary treatment required as
follows:
4.2.1 Type I—As electrodeposited without supplementary treatment.
4.2.2 Type II—With supplementary colored chromate treatment.
4.2.3 Type III—With supplementary colorless chromate treatment.
NOTE 3—It is strongly recommended that production items be processed as either Type II or Type III.
5. Ordering Information
5.1 In order to make the application of this specification complete, the purchaser needs to supply the following information to the
seller in the purchase order or other governing document:
5.1.1 The name, designation, and date of issue of this specification.
5.1.2 Deposit by class and type (4.1 and 4.2).
5.1.3 Composition and metallurgical conditionComposition, metallurgical condition, and tensile strength of the substrate to be
coated. Application to high-strength steel parts (6.2). ), pretreatment (6.3) and post treatment (6.7).
5.1.4 Heat treatment for stress relief, whether it has been performed or is required (6.3).
5.1.5 Additional undercoat, if required (6.5).
5.1.6 Plating process variation, if required (6.6).
5.1.7 Exception to stress relief heat treatment prior to plating (6.3).
5.1.8 Hydrogen embrittlement relief, if requiredBaking requirements after plating, if any (6.7).
5.1.9 Desired color of the Type II film (6.8.2).
5.1.10 Location of significant surfaces (7.1.2).
5.1.11 Coating luster (7.5).
5.1.12 Whether non-destructive or destructive tests are to be used in cases of choice (Note 14).
5.1.13 Configuration, procedures, and tensile load for hydrogen embrittlement relief test (9.4, 10.6, Supplementary Requirements
S2, and S3).
5.1.14 Whether certification is required (Section 12).
5.1.15 Whether supplementary requirements are applicable.
6. Materials and Manufacture
6.1 Nature of Coating—The coating shall be essentially pure cadmium produced by electrodeposition usually from an alkaline
cyanide solution.
6.2 High Tensile Strength Steel Parts—Steel parts having an ultimate tensile strength greater than 1650 MPa (approximately 50
HRC) shall not be plated by electrodeposition unless authorized by the purchaser.
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6.3 Stress Relief—Pretreatment of Iron or Steel for the Purpose of Reducing the Risk of Hydrogen Embrittlement—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-straightened shall be heat-treated at 190 6 15°C for 5 h or more greater than 1000 MPa (31 HRC) that contain
tensile stresses caused by cold forming or cold straightening which have not been heat treated after the cold forming process, shall
be heat treated for stress relief before cleaning and coating.to reduce the risk of hydrogen embrittlement in the part before clean
and electroplate processes. If these heat treatments are not required, the purchaser shall specify in the ordering information their
exception. If the purchaser does not specify an exception to heat treatment, then the plater shall use Table 1 in Specification B849
to determine the appropriate heat treatment for the steel based on its tensile strength.
6.4 Preparatory Procedures—The basis metal shall be subjected to such cleaning procedures as necessary to ensure a surface
satisfactory for subsequent electroplating. Materials used for cleaning shall have no damaging effects on the basis metal resulting
in pits, intergranular attack, stress corrosion cracking, or hydrogen embrittlement. If necessary, cleaning materials for steel parts
should be evaluated in accordance with Method F519.
NOTE 4—For basis metal preparation, the following standards should be employed depending upon the metallurgical composition: Practices B183, B242,
B253, B254, B281, B320, B322, B343, and B558.
6.5 Substrate—Cadmium shall be deposited directly on the basis metal part without an undercoat of another metal except when
the part is either stainless steel or aluminum and its alloys. An undercoat of nickel is permissible on stainless steel. With aluminum
and aluminum alloys, the oxide layer shall be removed and replaced by a metallic zinc layer in accordance with Guide B253. For
better adherence, a copper strike or a nickel coating may be applied to the zinc layer before electroplating with the cadmium.
6.6 Plating Process—The plating shall be applied after all basis metal heat treatments and mechanical operations, such as
machining, brazing, welding, forming, and perforating of the article, have been completed.
6.7 Hydrogen Embrittlement Relief—Steel Electroplated steel parts having a tensile strength of 1200 MPa (approximately 38
HRC) and higher greater than 1200 MPa (39 HRC) as well as surface hardened parts, shall be baked at 190 6 15°C for 8 h or
more within 4 h after electroplating to provide hydrogen embrittlement relief. Electroplated springs and other parts subject to
flexure shall not be flexed, loaded, or used before the hydrogen embrittlement relief treatment. The baking treatment for hydrogen
embrittlement relief shall be done before the application of any supplementary chromate treatment. When specified, freedom from
embrittlement shall be determined.to reduce the risk of hydrogen embrittlement. Baking of electroplated steel parts with tensile
strength 1200 MPa (39 HRC) or less is not mandatory.
6.7.1 Steel parts having a tensile strength greater than 1200 MPa (39 HRC) as well as surface hardened parts, shall be baked to
reduce the risk of hydrogen embrittlement. For such parts, purchasers shall specify the baking requirements in the ordering
information. Purchasers are directed to the appropriate ER Class in Guide B850 Table 1.
6.7.2 A purchaser wishing to specify baking requirements, irrespective of tensile strength, shall specify such requirements in the
ordering information. Purchasers are directed to Guide B850 Table 1.
6.7.3 Any baking treatment done under this section shall begin within 4 h of removal from the electroplating process.
6.7.4 Electroplated springs and other parts subject to flexure shall not be flexed before the hydrogen embrittlement relief treatment.
NOTE 5—For high-strength steels, greater than 1300 MPa or approximately 40 HRC, it is strongly recommended that the baking time be extended to 23
h or more to ensure hydrogen embrittlement relief.
NOTE 6—Electroplated steel parts, passivated by the baking operation for hydrogen embrittlement relief, require reactivation before the chromate
treatment. This application, immersion in a dilute acid solution, should be done as soon as practical. If the chromating solution contains sulfuric acid,
then the reactivating solution should be 1 part of sulfuric acid (sp gr 1.83) by volume added to 99 parts of water. If the chromating solution contains
hydrochloric acid, then the reactivating solution should be 1 part of hydrochloric acid (sp gr 1.16) by volume added to 99 parts of water. Duration of
immersion should be as brief as is consistent with the nature of the work. Separately racked items can be reactivated in approximately 5 s, whereas a
perforated container of barrel-plated parts requires approximately 15 s.
6.8 Chromate Treatment:
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6.8.1 Chromate treatments for Types II and III shall be done in or with special aqueous acidic solutions composed of hexavalent
chromium along with certain anions that act as catalyst or film-forming compounds to produce a continuous smooth protective film.
Chromic acid and nitric acid bright dips shall not be used for treatment to produce chromate coatings. When proprietary materials
are used for this treatment, the instructions of the supplier should be followed.
6.8.2 The Type II film color shall range from an iridescent yellow or a thicker, more protective iridescent bronze or brown to the
heavier olive drab. It may also be dyed to a desired color. When necessary, the color of the film shall be indicated by the purchaser
and specified by the provision of a suitably colored sample or indicated on the drawing for the part.
6.8.3 The absence of color shall not be considered as evidence of lack of Type III film or as a basis for rejection. Presence of clear
Type III film shall be determined by a spot test as specified in 10.4.
6.8.4 Waxes, lacquers, or other organic coatings shall not be used as a substitute for, nor may they be used in conjunction with,
supplementary treatments when the purpose is to ensure conformance to the salt spray requirements. Waxes and the like, may be
used to improve lubricity.
7. Coating Requirements
7.1 Thickness:
7.1.1 The thickness of the coating everywhere on the significant surfaces shall conform to the requirements of the specified class,
as defined in 4.1.
7.1.2 Significant surfaces are those normally visible (directly or by reflection) that are essential to the appearance or serviceability
of the article when assembled in normal position; or that can be the source of corrosion products that will deface visible surfaces
on the assembled article. When necessary, the significant surfaces shall be indicated by the purchaser on applicable drawing of the
article, or by the provision of suitably marked samples.
NOTE 7—As heavier coatings are required for satisfactory corrosion resistance than Class 5, allowance should be made in the fabrication of most threaded
articles, such as nuts, bolts, and similar fasteners with complementary threads for dimensional tolerances to obtain necessary coating build-up. Flat
surfaces and certain shielded or recessed areas, such as root-diameter of threads, have a tendency to exhibit lack of build-up and to be heavier at exposed
edges and sharp projections with electrodeposited coatings. This trend is also found with vacuum-deposited cadmium coatings and is in direct contrast
with mechanically deposited coatings.
NOTE 8—The coating thickness requirements of this specification is a minimum requirement. Variation in thickness from point to point on an article is
inherent in electroplating. Therefore, the thickness will have to exceed the specified value at some points on the significant surfaces to ensure that it equals
or exceeds the specified value at all points. Hence, in most cases, the average coating thickness of an article will be greater than the specified value; how
much greater is largely determined by the shape of the article (see Practice B507) and the characteristics of the electroplating process. In addition, the
average coating thickness on articles will vary from article to article within a production lot. Therefore, if all of the articles in a production lot are to meet
the thickness requirement, the average coating thickness for the production lot as a whole will be greater than the average necessary to assure that a single
article meets the requirement.
7.1.3 For nonsignificant visible surfaces, the minimum thickness for Classes 25 and 12 shall be Class 8 (8 μm); for Class 8 it shall
be Class 5 (5 μm); and for Class 5 it shall be 4 μm.
7.2 Adhesion—The cadmium coating shall be sufficiently adherent to the basis metal to pass the tests detailed in 10.2.
7.3 Abrasion Resistant—The supplementary Type II chromate film shall be adherent, nonpowdery, and abrasion resistant (10.3).
7.4 Corrosion Resistance—Cadmium coatings with supplementary chromate films on iron and steel basis metals shall show
neither white corrosion products of cadmium nor basis metal corrosion products at the end of 96 h for Type II film or 12 h for Type
III film when tested by continuous exposure to salt spray. The appearance of corrosion products visible to the unaided eye at normal
reading distance shall be cause for rejection, except white corrosion products at the edges of specimens shall not constitute failure.
NOTE 9—The hours given are the minimum required to guarantee satisfactory performance. Longer periods before the appearance of white corrosion and
basis metal corrosion (rust from iron and steel products) are possible. Salt spray resistance does not vary in exact proportion with increased plating
thicknesses of Types II and III coatings. Although specified hours to failure (red rust for iron and steel articles) for Type I coating is not stated, the hours
given for Types II and III reflect the added protection of the chromate treatment without requiring impractical testing.
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NOTE 10—In many instances, there is no direct relation between the results of an accelerated corrosion test and the resistance to corrosion in other media.
Factors such as the formation of protective films, basis materials, and temperature can influence the progress of corrosion greatly, depending upon the
conditions encountered in service. The results obtained in the test should, therefore, not be regarded as a direct guide to the corrosion resistance of the
tested materials in all environments where these materials may be used. Also, performance of different materials in the test cannot always be taken as
a direct guide to the relative corrosion of these materials in service.
7.5 Luster—Either a bright or dull luster shall be acceptable; however, for steel parts that are heat treated to 40 HRC
(approximately 1300 MPa) and harder, they shall have a dull luster or finish.
NOTE 11—High-strength steel parts that are cadmium plated from baths without brighteners are much more permeable to hydrogen than those bright
cadmium plated. Bright cadmium is a very good hydrogen barrier that “seals in” the hydrogen. As embrittlement is a surface or subsurface phenomenon,
even a 24 h baking is not sufficient to provide embrittlement relief of high-strength steels plated with a Class 12 deposit from a bright cyanide plating
bath.
7.6 Workmanship and Finish—The coating shall be smooth, adherent, uniform in appearance, and free from blisters, pits, nodules,
flaking, and other defects that may affect the function of the coating. The coating shall cover all surfaces as stated in 7.1, including
thread roots, thread peaks, corners, holes, recesses, and edges. There shall be no indication of contamination or improper operation
of equipment used to produce the deposit, such as excessively powdery or darkened coatings. Superficial staining and variations
in color or luster shall not be cause for r
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