ASTM B605-22

Standard Specification for Electrodeposited Coatings of Tin-Nickel Alloy

ABSTRACT
This specification establishes the requirements for electrodeposited tin-nickel alloy coatings from aqueous solutions intended for the corrosion protection of fabricated articles of iron, steel, zinc-base alloys, copper, and copper alloys. This specification does not apply to sheets, strips, or wires in the fabricated form. It also may not be applicable to finely threaded articles, but the decision to use the coating on such components may be made by the purchaser. Coating grades shall be designated by a service condition number, which indicates the severity of exposure for which the coating is intended, and a coating thickness notation. Iron and steel specimens shall undergo pre- and post-coating treatments for reducing the risk of hydrogen embrittlement. Coatings shall be sampled, tested, and conform to specified requirements as to appearance (visible defects), composition, thickness (assessed either by microscopical, magnetic, coulometric, beta backscatter, or X-ray spectrometry), adhesion (determined either by burnishing, or heat-quench test), and integrity (including gross defects, mechanical damage, and porosity).
SCOPE
1.1 This specification covers the requirements for electrodeposited tin-nickel alloy coatings from aqueous solutions intended for the corrosion protection of fabricated articles of iron, steel, zinc-base alloys, copper, and copper alloys. The composition of the alloy remains constant at 65/35 tin-nickel in spite of wide fluctuations in both composition and operating conditions. The composition corresponds quite closely to an equiatomic ratio, and the process favors the co-deposition of tin and nickel atoms at identical rates.  
1.2 This specification does not apply to sheet, strip, or wire in the fabricated form. It also may not be applicable to threaded articles having basic major diameters up to and including 19 mm because of the nonuniformity of thickness that can be expected on fine threads. However, a decision to use the coating on such components may be made by the purchaser.  
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 14-Nov-2022
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.06 - Soft Metals

Relations

• 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 B571-23 - Standard Practice for Qualitative Adhesion Testing of Metallic Coatings
• Effective Date: 01-Nov-2023
• Refers: ASTM B765-03(2023) - Standard Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
• Effective Date: 01-Nov-2023
• Refers: ASTM D3951-18(2023) - Standard Practice for Commercial Packaging
• Effective Date: 01-Oct-2023
• 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 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 B809-95(2018) - Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor (“Flowers-of-Sulfur”)
• Effective Date: 01-Aug-2018
• Refers: ASTM B571-18 - Standard Practice for Qualitative Adhesion Testing of Metallic Coatings
• Effective Date: 01-Aug-2018
• Refers: ASTM B765-03(2018) - Standard Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
• Effective Date: 01-Aug-2018
• Refers: ASTM D3951-18 - Standard Practice for Commercial Packaging
• Effective Date: 01-May-2018
• Refers: ASTM D3951-15 - Standard Practice for Commercial Packaging
• Effective Date: 01-Dec-2015
• 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 B634-14 - Standard Specification for Electrodeposited Coatings of Rhodium for Engineering Use
• Effective Date: 01-Sep-2014
• Refers: ASTM B765-03(2013) - Standard Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
• Effective Date: 01-Dec-2013

Overview

ASTM B605-22: Standard Specification for Electrodeposited Coatings of Tin-Nickel Alloy provides comprehensive requirements for tin-nickel alloy coatings applied via electrodeposition from aqueous solutions. These coatings are engineered primarily for corrosion protection of fabricated articles made from iron, steel, zinc-base alloys, copper, and copper alloys. The standard specifies a consistent alloy composition of 65% tin and 35% nickel, aiming for maximum corrosion resistance and durability.

The standard is widely referenced in industries where effective and robust metallic coatings are required, particularly for components exposed to harsh environments. ASTM B605-22 addresses coating appearance, adhesion, thickness, integrity, and necessary pre- and post-coating treatments-especially for preventing hydrogen embrittlement in high-strength steels.

Key Topics

Scope and Limitations

• Applies to electrodeposited tin-nickel coatings on fabricated articles, excluding sheet, strip, and wire forms.
• May not be suitable for finely threaded articles, though final applicability rests with the purchaser.
• Coating grades are specified by service condition numbers, indicating exposure severity, and by minimum thickness.

Coating Composition and Process

• The tin-nickel ratio remains at 65/35, ensuring consistent co-deposition rates.
• The alloy deposit is typically single-phase, providing high corrosion resistance and hardness, but is somewhat brittle.
• Copper undercoating may be required based on substrate type and service condition for improved adhesion and diffusion barrier.

Coating Performance and Inspection

• Clear criteria for assessment: coatings must be smooth, continuous, adherent, and free from visible defects.
• Minimum thickness requirements vary with substrate and intended service conditions, ensuring sufficient protection.
• Coatings undergo regular sampling and testing for:
  • Appearance and freedom from defects
  • Thickness by several recognized test methods (including X-ray, magnetic, and coulometric)
  • Adhesion using burnishing or heat-quench tests
  • Integrity, including gross defects, mechanical damage, and porosity

Safety and Regulatory Compliance

• Users are responsible for establishing safety, health, and environmental practices aligned with regulatory requirements.

Applications

Industrial and Engineering Uses

• Extended Severe Service: Used on equipment exposed to continuous abrasion or aggressive chemicals, such as pumps, valves, and flow control devices.
• Severe/Very Severe Service: Suitable for cooking utensils, analytical weights, and surgical instruments where resistance to damp, industrial atmospheres is critical.
• Moderate/Mild Service: Applied to electronic components, watch parts, and as an etch resist in printed circuit boards. Also used as a final finish enhanced by additional coatings for improved solderability.

Key Benefits

• Provides superior corrosion resistance, especially in harsh and industrial environments
• Ensures long-term integrity for critical components
• Reduces risks such as hydrogen embrittlement through specified pre- and post-coating treatments

Related Standards

ASTM B605-22 references and works in tandem with several other ASTM standards, including:

• ASTM B183: Preparation of Low-Carbon Steel for Electroplating
• ASTM B242: Preparation of High-Carbon Steel for Electroplating
• ASTM B252: Preparation of Zinc Alloy Die Castings for Electroplating
• ASTM B281: Preparation of Copper and Copper Alloys for Electroplating
• ASTM B322: Cleaning Metals Prior to Electroplating
• ASTM B487, B499, B504, B567, B568: Thickness measurement methods
• ASTM B571: Adhesion testing of metallic coatings
• ASTM B849, B850: Pre- and post-coating treatments for hydrogen embrittlement
• ASTM D3951: Commercial packaging practices

These related standards support the implementation, testing, and quality control provisions defined in ASTM B605-22, making them essential references for manufacturing, quality assurance, and supply chain professionals working with electrodeposited tin-nickel alloy coatings.

Keywords: ASTM B605-22, tin-nickel alloy, electrodeposited coatings, corrosion protection, coating thickness, hydrogen embrittlement, industrial coatings, copper undercoating, metallic coatings, ASTM standards.

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: B605 −22
Standard Specification for
Electrodeposited Coatings of Tin-Nickel Alloy
This standard is issued under the fixed designation B605; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* B183Practice for Preparation of Low-Carbon Steel for
Electroplating
1.1 Thisspecificationcoverstherequirementsforelectrode-
B242Guide for Preparation of High-Carbon Steel for Elec-
posited tin-nickel alloy coatings from aqueous solutions in-
troplating
tended for the corrosion protection of fabricated articles of
B246Specification for Tinned Hard-Drawn and Medium-
iron, steel, zinc-base alloys, copper, and copper alloys. The
Hard-Drawn Copper Wire for Electrical Purposes
compositionofthealloyremainsconstantat65/35tin-nickelin
B252Guide for Preparation of Zinc Alloy Die Castings for
spite of wide fluctuations in both composition and operating
Electroplating and Conversion Coatings
conditions. The composition corresponds quite closely to an
B281Practice for Preparation of Copper and Copper-Base
equiatomic ratio, and the process favors the co-deposition of
Alloys for Electroplating and Conversion Coatings
tin and nickel atoms at identical rates.
B322Guide for Cleaning Metals Prior to Electroplating
1.2 This specification does not apply to sheet, strip, or wire
B374Terminology Relating to Electroplating
inthefabricatedform.Italsomaynotbeapplicabletothreaded
B487Test Method for Measurement of Metal and Oxide
articles having basic major diameters up to and including
Coating Thickness by Microscopical Examination of
19mm because of the nonuniformity of thickness that can be
Cross Section
expected on fine threads. However, a decision to use the
B499Test Method for Measurement of CoatingThicknesses
coating on such components may be made by the purchaser.
by the Magnetic Method: Nonmagnetic Coatings on
1.3 Units—The values stated in SI units are to be regarded
Magnetic Basis Metals
asstandard.Nootherunitsofmeasurementareincludedinthis
B504Test Method for Measurement of Thickness of Metal-
standard.
lic Coatings by the Coulometric Method
B507Practice for Design ofArticles to Be Electroplated on
1.4 This standard does not purport to address all of the
Racks
safety concerns, if any, associated with its use. It is the
B567Test Method for Measurement of Coating Thickness
responsibility of the user of this standard to establish appro-
by the Beta Backscatter Method
priate safety, health, and environmental practices and deter-
B568Test Method for Measurement of Coating Thickness
mine the applicability of regulatory limitations prior to use.
by X-Ray Spectrometry
1.5 This international standard was developed in accor-
B571Practice for Qualitative Adhesion Testing of Metallic
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the Coatings
B602Guide for Attribute Sampling of Metallic and Inor-
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical ganic Coatings
B634Specification for Electrodeposited Coatings of Rho-
Barriers to Trade (TBT) Committee.
dium for Engineering Use
2. Referenced Documents
B697Guide for Selection of Sampling Plans for Inspection
of Electrodeposited Metallic and Inorganic Coatings
2.1 ASTM Standards:
B762GuideofVariablesSamplingofMetallicandInorganic
Coatings
This specification is under the jurisdiction of ASTM Committee B08 on
B765GuideforSelectionofPorosityandGrossDefectTests
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
for Electrodeposits and Related Metallic Coatings
B08.06 on Soft Metals.
B809Test Method for Porosity in Metallic Coatings by
Current edition approved Nov. 15, 2022. Published December 2022. Originally
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
approved in 1975. Last previous edition approved in 2015 as B605–95a(2015).
DOI: 10.1520/B0605-22.
B849Specification for Pre-Treatments of Iron or Steel for
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Reducing Risk of Hydrogen Embrittlement
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
B850GuideforPost-CoatingTreatmentsofSteelforReduc-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. ing the Risk of Hydrogen Embrittlement
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B605 − 22
TABLE 2 Tin-Nickel Coatings on Copper or Copper Alloys
D3951Practice for Commercial Packaging
Service Minimum
Thickness
Condition Thickness,
3. Terminology
Notation
Number µm
3.1 Definitions:
A B B
5 Cu/Sn-Ni as specified as specified
3.1.1 Many terms used in this standard are defined in
(above 45) (above 45)
A
4 Cu/Sn-Ni 45 45
Terminology B374.
A
3 Cu/Sn-Ni 25 25
3.1.2 significant surface, n—that portion of a coated arti-
A
2 Cu/Sn-Ni 15 15
A
cle’s surface where the coating is required to meet all the 0 Cu/Sn-Ni 44
A
requirements of the coating specification for that article.
An undercoating of copper 4.0 µm thick shall be applied on copper-zinc alloys to
serve as a zinc diffusion barrier.
Significant surfaces are those that are essential to the service-
B
Thickness of Sn-Ni shall be stated in a Thickness Notation. A statement of
ability or function of the article, or which can be a source of
Service Condition 5 is not sufficient.
corrosion products or tarnish films that interfere with the
function or desirable appearance of the article. Significant
surfaces are those surfaces that are identified by the purchaser
TABLE 3 Tin-Nickel Coatings on Zinc Alloys
by, for example, indicating them on an engineering drawing of
Service Minimum
Thickness
Condition Thickness,
the product or marking a sample item of the product.
Notation
Number µm
3.1.3 undercoating, n—a metallic coating layer between the
A
4 Zn/Cu /Sn-Ni 45 45
A
basis metal or substrate and the topmost metallic coating. The
3 Zn/Cu /Sn-Ni 25 25
A
thickness of an undercoating is usually greater than 0.8µm. 2 Zn/Cu /Sn-Ni 15 15
A
1 Zn/Cu /Sn-Ni 8 8
This is in contrast to strikes or flashes, whose thicknesses are
A
An undercoating of copper 4.0 µm thick shall be applied to prevent zinc from
generally lower.
contaminating the Sn-Ni plating bath and to serve as a diffusion barrier.
4. Classifications
4.1 Coating Grades—Six grades of coatings, designated by
service condition numbers, are covered by this specification.
For each coating grade a coating thickness grade is specified
5. Ordering Information
(see Tables 1-3).
5.1 To make the application of this standard complete, the
4.2 Service Condition Number—Theserviceconditionnum-
purchaser needs to supply the following information to the
ber indicates the severity of exposure for which the grade of
seller in the purchase order or other government documents.
coating is intended.
5.1.1 The name, designation, and date of issue of this
SC5—extended severe service
standard,
SC4—very severe service
5.1.2 Location of significant surface(s) (see section 3.1.2),
SC3—severe service
SC2—moderate service
5.1.3 The service number or coating thickness notation (see
SC1—mild service
4.2 and 4.3),
SC0—mild service (copper and copper alloys only)
5.1.4 Undercoating, if required (see 6.2 and Tables 1-3),
NOTE 1—Typical service conditions for which the service condition
5.1.5 Any requirement for submission of sample coated
numbers are appropriate are given in Appendix X1.
articles (see 7.2.1),
4.3 Coating Thickness Notation—The coating thickness is
5.1.6 Whether or not location of rack marks is to be defined
specified for each service condition in the following manner:
(see 7.2.1),
Basis metal/Undercoating (thickness)/Sn-Ni (thickness). For
5.1.7 Any requirement for porosity testing and the criteria
example, Fe/Cu4/Sn-Ni25 would indicate a 25 µm tin-nickel
for acceptance (see 7.5.2),
coating over an iron or steel article with a 4µm thick copper
5.1.8 Basis metal alloy designation and ultimate tensile
undercoating. All thickness notations are minimum thick-
strength of the steel,
nesses.
5.1.9 Whether the part underwent cold forming or cold
straightening subsequent to heat treatment (see Note 2),
5.1.10 Exception to heat treatment for stress relief prior to
TABLE 1 Tin-Nickel Coatings on Steel
plating (see 7.6),
Service Minimum
Thickness
Condition Thickness,
5.1.11 Baking requirements after electroplating, if required
Notation
Number µm
(see 7.7),
A B B
5 Fe/Cu /Sn-Ni as specified as specified
5.1.12 Any packaging requirement (see section 7.8),
(above 45) (above 45)
A
4 Fe/Cu /Sn-Ni 45 45
5.1.13 Inspection procedure to be used (see Section 9),
A
3 Fe/Cu /Sn-Ni 25 25
5.1.14 Any requirement for certification (see Section 11),
2 Fe/Sn-Ni 15 15
and
1 Fe/Sn-Ni 8 8
A
5.1.15 Any requirement for test specimens (see 8.1.1).
Copper undercoat shall be at least 4.0 µm.
B
Thickness of Sn-Ni shall be stated in a Thickness Notation. A statement of
NOTE 2—Information in 5.1.8 and 5.1.9 is necessary for proper
Service Condition 5 is not sufficient.
pretreatment (7.6) and post coating treatment (7.7) if applicable.
B605 − 22
substrate over which they are applied is smooth and free of torn metal,
6. Material and Process
inclusions, pores, and other defects. The specifications covering the
6.1 Composition of Coating—Electrolytes that have been
unfinishedproductshouldprovidelimitsforthesedefects.Ametalfinisher
investigated for producing Sn-Ni alloy deposits include
can often remove defects through special treatments, such as grinding,
polishing, abrasive blasting, chemical etches, and electropolishing.
cyanide, fluoborate, pyrophosphate, and acetate, but the only
However, these are not normal in the treatment steps preceding the
one in general commercial use is the fluoride-chloride formu-
application of the coating. When they are desired, they are the subject of
lation. Thedepositcontains35 65%nickelwiththeremain-
special agreement between the purchaser and the seller.
der tin (see Note 3).
NOTE 6—Proper preparatory procedures and thorough cleaning are
essential to ensure satisfactory adhesion and corrosion resistance perfor-
NOTE 3—The electrodeposited tin-nickel coating is a single-phase,
mance of the coating. Materials used for cleaning should not damage the
metastable compound, corresponding approximately to the formula SnNi.
basis metal, for example, by causing defects such as pits, intergranular
It is stable at ordinary temperatures but starts to recrystallize at elevated
attack, stress corrosion cracking, and unwarranted hydrogen embrittle-
temperatures. The safe working temperature of the coating is 300°C,
ment. It is recommended that the following Practices, where appropriate
althoughactualmeltingdoesnotcommencebelow800°C.Thecoatingis
for cleaning, be used: B183, B242, B252, B281, and B322.
hard (700HV100). Like many such compounds, it is inherently somewhat
brittle, but if it is free of internal stresses, the brittleness is not sufficient
7.3 Thickness:
to impair its serviceability or to cause the coating to flake under impact.
7.3.1 The thickness of the coating everywhere on the
Because of the brittleness of the tin-nickel, however, it is not possible to
significantsurfacesshallconformtotherequirementsinTables
fabricate parts by bending coated sheet material, because the compressive
1-3 as to minimum thickness.
stresses in the coating on the inside of the bend usually cause some of the
coating to flake off. To provide serviceability, the coating must be
NOTE 7—The thickness of electrodeposited coatings varies from point
depositedinastress-freecondition.Inaddition,itisgenerallyinadvisable
to point on the surface of the product. (See Practice B507.)The thickness
to specify tin-nickel finish for parts subject to deformation in service.
is less in interior corners and holes. Such surfaces are often exempt from
6.2 Basis Metal—Tin-nickel can be deposited directly on
thickness requirements. If the full thickness is required in those locations,
the electroplater will have to use special techniques that will probably
steel, copper, and copper-base alloys. However, an undercoat-
raise the cost of the process.
ing of copper can improve performance in some systems and
NOTE 8—The coating thickness requirement of this specification is a
shall be used under the following conditions:
minimum. Variation in the thickness from point to point on an article and
6.2.1 On steel, a copper undercoating with a minimum
from article to article in a production lot is inherent in electroplating.
thickness of 4 µm, shall be used for Service Conditions 3, 4,
Therefore, if all of the articles in a production are to meet the thickness
and 5. requirement, the average coating thickness for the production lot as a
whole will be greater than the specified minimum.
6.2.2 On copper-zinc alloys, a copper undercoating with a
minimum thickness of 4 µm shall be used for all service
7.4 Adhesion—The coatings shall be adherent to the basis
conditions to prevent diffusion of the zinc.
metal when subject to either test, in accordance with 8.5.2 and
6.2.3 Zinc-base alloys shall have an undercoating of a
8.5.3. There shall be no separation of the coating from the
minimum of 4µm of copper to prevent diffusion of the zinc
substrate.
intothedepositandtopreventcontaminationoftheelectrolyte
7.5 Integrity of the Coating:
with zinc.
7.5.1 Gross Defects/Mechanical Damage—The coatings
NOTE 4—Tin-nickel-coated zinc-alloy diecastings shall never be re-
shall be free of mechanical damage, large pores, and similar
turned for remelting to prevent contamination of the zinc alloy with tin.
gross defects. For some applications, this requirement may be
relaxed to allow for a small number of such defects (per unit
7. Coating Requirements
area), especially if they are outside the significant surfaces.
7.1 Composition of Coating—The deposit shall contain
7.5.2 Porosity—Almostallas-platedelectrodepositscontain
65 65% tin, the balance nickel.
some porosity. The amount of porosity that may be tolerable
depends on the severity of the environment that the article is
7.2 Appearance:
likely to encounter during service or storage. If the pores are
7.2.1 The coating on all readily visible surfaces shall be
few in number or away from significant surfaces, their pres-
smooth, fine grained, continuous, adherent, free of visible
ence can often be tolerated. Such acceptance (or pass-fail)
blisters, pits, nodules, indications of burning, excessive
criteria shall be part of the product specification for the
buildup, staining, and other defects. All tin-nickel coated
particular article or coating requiring the porosity test (see 8.6
articles shall be clean and undamaged. When necessary,
for porosity test methods).
preliminary samples showing the finish shall be supplied for
approval. Where a rack contact mark is unavoidable, its
7.6 Pre-Treatments of Iron and Steel for Reducing the Risk
location shall be indicated on the article or its drawing.
of Hydrogen Embrittlement—Steel parts having an ultimate
7.2.2 Defects and variations in appearance in the coating
tensile strength greater than 1000MPa (31HRC) that contain
that arise from surface conditions of the substrate (scratches,
tensile stresses caused by cold forming or cold straightening
pores, roll marks, inclusions, and the like) and that persist in
which have not been heat treated after the cold forming
the coating despite the observance of good metal finishing
process, shall be heat treated for stress relief to reduce the risk
practices shall not be cause for rejection.
of hydrogen embrittlement in the part before clean and
electroplateprocesses.Iftheseheattreatmentsarenotrequired,
NOTE 5—Coatings generally perform better in service when the
the purchaser shall specify in the ordering information their
exception. If the purchaser does not specify an exception to
Lowenheim, F. A., Electroplating, McGra
...

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: B605 − 95a (Reapproved 2015) B605 − 22
Standard Specification for
Electrodeposited Coatings of Tin-Nickel Alloy
This standard is issued under the fixed designation B605; 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.
1. Scope Scope*
1.1 This specification covers the requirements for electrodeposited tin-nickel alloy coatings from aqueous solutions intended for
the corrosion protection of fabricated articles of iron, steel, zinc-base alloys, copper, and copper alloys. The composition of the
alloy remains constant at 65/35 tin-nickel in spite of wide fluctuations in both composition and operating conditions. The
composition corresponds quite closely to an equiatomic ratio, and the process favors the co-deposition of tin and nickel atoms at
identical rates.
1.2 This specification does not apply to sheet, strip, or wire in the fabricated form. It also may not be applicable to threaded articles
having basic major diameters up to and including 19 mm 19 mm because of the nonuniformity of thickness that can be expected
on fine threads. However, a decision to use the coating on such components may be made by the purchaser.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.4 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 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 ASTM Standards:
B183 Practice for Preparation of Low-Carbon Steel for Electroplating
B242 Guide for Preparation of High-Carbon Steel for Electroplating
B246 Specification for Tinned Hard-Drawn and Medium-Hard-Drawn Copper Wire for Electrical Purposes
B252 Guide for Preparation of Zinc Alloy Die Castings for Electroplating and Conversion Coatings
B281 Practice for Preparation of Copper and Copper-Base Alloys for Electroplating and Conversion Coatings
B322 Guide for Cleaning Metals Prior to Electroplating
B374 Terminology Relating to Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
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, 2015Nov. 15, 2022. Published April 2015December 2022. Originally approved in 1975. Last previous edition approved in 20092015
as B605 – 95a (2009).(2015). DOI: 10.1520/B0605-95AR15.10.1520/B0605-22.
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.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B605 − 22
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
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
B634 Specification for Electrodeposited Coatings of Rhodium for Engineering Use
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B762 Guide of Variables Sampling of Metallic and Inorganic Coatings
B765 Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
B809 Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor (“Flowers-of-Sulfur”)
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
D3951 Practice for Commercial Packaging
3. Terminology
3.1 Definitions:
3.1.1 Many terms used in this standard are defined in Terminology B374.
3.1.2 significant surface—surface, n—that portion of a coated article’s surface where the coating is required to meet all the
requirements of the coating specification for that article. Significant surfaces are those that are essential to the serviceability or
function of the article, or which can be a source of corrosion products or tarnish films that interfere with the function or desirable
appearance of the article. Significant surfaces are those surfaces that are identified by the purchaser by, for example, indicating
them on an engineering drawing of the product or marking a sample item of the product.
3.1.3 undercoating—undercoating, n—a metallic coating layer between the basis metal or substrate and the topmost metallic
coating. The thickness of an undercoating is usually greater than 0.8 μm. 0.8 μm. This is in contrast to strikes or flashes, whose
thicknesses are generally lower.
4. Classifications
4.1 Coating Grades—Six grades of coatings, designated by service condition numbers, are covered by this specification. For each
coating grade a coating thickness grade is specified (see Tables 1-3).
4.2 Service Condition Number—The service condition number indicates the severity of exposure for which the grade of coating
is intended.
SC5—extended severe service
SC4—very severe service
SC3—severe service
SC2—moderate service
SC1—mild service
SC0—mild service (copper and copper alloys only)
TABLE 1 Tin-Nickel Coatings on Steel
Service Minimum
Thickness
Condition Thickness,
Notation
Number μm
A B B
5 Fe/Cu /Sn-Ni as specified as specified
(above 45) (above 45)
A
4 Fe/Cu /Sn-Ni 45 45
A
3 Fe/Cu /Sn-Ni 25 25
2 Fe/Sn-Ni 15 15
1 Fe/Sn-Ni 8 8
A
Copper undercoat shall be at least 4.0 μm.
B
Thickness of Sn-Ni shall be stated in a Thickness Notation. A statement of
Service Condition 5 is not sufficient.
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TABLE 2 Tin-Nickel Coatings on Copper or Copper Alloys
Service Minimum
Thickness
Condition Thickness,
Notation
Number μm
A B B
5 Cu/Sn-Ni as specified as specified
(above 45) (above 45)
A
4 Cu/Sn-Ni 45 45
A
3 Cu/Sn-Ni 25 25
A
2 Cu/Sn-Ni 15 15
A
0 Cu/Sn-Ni 4 4
A
An undercoating of copper 4.0 μm thick shall be applied on copper-zinc alloys to
serve as a zinc diffusion barrier.
B
Thickness of Sn-Ni shall be stated in a Thickness Notation. A statement of
Service Condition 5 is not sufficient.
TABLE 3 Tin-Nickel Coatings on Zinc Alloys
Service Minimum
Thickness
Condition Thickness,
Notation
Number μm
A
4 Zn/Cu /Sn-Ni 45 45
A
3 Zn/Cu /Sn-Ni 25 25
A
2 Zn/Cu /Sn-Ni 15 15
A
1 Zn/Cu /Sn-Ni 8 8
A
An undercoating of copper 4.0 μm thick shall be applied to prevent zinc from
contaminating the Sn-Ni plating bath and to serve as a diffusion barrier.
NOTE 1—Typical service conditions for which the service condition numbers are appropriate are given in Appendix X1.
4.3 Coating Thickness Notation—The coating thickness is specified for each service condition in the following manner: Basis
metal/Undercoating (thickness)/Sn-Ni (thickness). For example, Fe/Cu4/Sn-Ni25 would indicate a 25 μm tin-nickel coating over
an iron or steel article with a 4-μm4 μm thick copper undercoating. All thickness notations are minimum thicknesses.
5. Ordering Information
5.1 To make the application of this standard complete, the purchaser needs to supply the following information to the seller in the
purchase order or other government documents.
5.1.1 The name, designation, and date of issue of this standard,
5.1.2 Location of significant surface(s) (see section 3.1.2),
5.1.3 The service number or coating thickness notation (see 4.2 and 4.3),
5.1.4 Undercoating, if required (see 6.2 and Tables 1-3),
5.1.5 Any requirement for submission of sample coated articles (see 7.2.1),
5.1.6 Whether or not location of rack marks is to be defined (see 7.2.1),
5.1.7 Any requirement for porosity testing and the criteria for acceptance (see 7.5.2),
5.1.8 Basis metal alloy designation and ultimate tensile strength of the steel,
5.1.9 Whether the part underwent cold forming or cold straightening subsequent to heat treatment (see Note 2),
5.1.10 Heat Exception to heat treatment for stress relief, whether it has been performed by the purchaser, or is required relief prior
to plating (see 7.6),
5.1.11 Heat treatmentBaking requirements after electroplating, if required (see 7.7),
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5.1.12 Any packaging requirement (see section 7.8),
5.1.13 Inspection procedure to be used (see Section 9),
5.1.14 Any requirement for certification (see Section 11), and
5.1.15 Any requirement for test specimens (see 8.1.1).
NOTE 2—Information in 5.1.8 and 5.1.9 is necessary for proper pretreatment (7.6) and post coating treatment (7.7) if applicable.
6. Material and Process
6.1 Composition of Coating—Electrolytes that have been investigated for producing Sn-Ni alloy deposits include cyanide,
fluoborate, pyrophosphate, and acetate, but the only one in general commercial use is the fluoride-chloride formulation. The
deposit contains 35 6 5 % nickel with the remainder tin (see Note 23).
NOTE 3—The electrodeposited tin-nickel coating is a single-phase, metastable compound, corresponding approximately to the formula SnNi. It is stable
at ordinary temperatures but starts to recrystallize at elevated temperatures. The safe working temperature of the coating is 300°C,300 °C, although actual
melting does not commence below 800°C.800 °C. The coating is hard (700HV100). Like many such compounds, it is inherently somewhat brittle, but
if it is free of internal stresses, the brittleness is not sufficient to impair its serviceability or to cause the coating to flake under impact. Because of the
brittleness of the tin-nickel, however, it is not possible to fabricate parts by bending coated sheet material, because the compressive stresses in the coating
on the inside of the bend usually cause some of the coating to flake off. To provide serviceability, the coating must be deposited in a stress-free condition.
In addition, it is generally inadvisable to specify tin-nickel finish for parts subject to deformation in service.
6.2 Basis Metal—Tin-nickel can be deposited directly on steel, copper, and copper-base alloys. However, an undercoating of
copper can improve performance in some systems and shall be used under the following conditions:
6.2.1 On steel, a copper undercoating with a minimum thickness of 4 μm, shall be used for Service Conditions 3, 4, and 5.
6.2.2 On copper-zinc alloys, a copper undercoating with a minimum thickness of 4 μm shall be used for all service conditions to
prevent diffusion of the zinc.
6.2.3 Zinc-base alloys shall have an undercoating of a minimum of 4 μm 4 μm of copper to prevent diffusion of the zinc into the
deposit and to prevent contamination of the electrolyte with zinc.
NOTE 4—Tin-nickel-coated zinc-alloy diecastings shall never be returned for remelting to prevent contamination of the zinc alloy with tin.
7. Coating Requirements
7.1 Composition of Coating—The deposit shall contain 65 6 5 % tin, the balance nickel.
7.2 Appearance:
7.2.1 The coating on all readily visible surfaces shall be smooth, fine grained, continuous, adherent, free of visible blisters, pits,
nodules, indications of burning, excessive buildup, staining, and other defects. All tin-nickel coated articles shall be clean and
undamaged. When necessary, preliminary samples showing the finish shall be supplied for approval. Where a rack contact mark
is unavoidable, its location shall be indicated on the article or its drawing.
7.2.2 Defects and variations in appearance in the coating that arise from surface conditions of the substrate (scratches, pores, roll
marks, inclusions, and the like) and that persist in the coating despite the observance of good metal finishing practices shall not
be cause for rejection.
NOTE 5—Coatings generally perform better in service when the substrate over which they are applied is smooth and free of torn metal, inclusions, pores,
and other defects. The specifications covering the unfinished product should provide limits for these defects. A metal finisher can often remove defects
through special treatments, such as grinding, polishing, abrasive blasting, chemical etches, and electropolishing. However, these are not normal in the
Lowenheim, F. A., Electroplating, McGraw-Hill Inc., 1978.
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treatment steps preceding the application of the coating. When they are desired, they are the subject of special agreement between the purchaser and the
seller.
NOTE 6—Proper preparatory procedures and thorough cleaning are essential to ensure satisfactory adhesion and corrosion resistance performance of the
coating. Materials used for cleaning should not damage the basis metal, for example, by causing defects such as pits, intergranular attack, stress corrosion
cracking, and unwarranted hydrogen embrittlement. It is recommended that the following Practices, where appropriate for cleaning, be used: B183, B242,
B252, B281, and B322.
7.3 Thickness:
7.3.1 The thickness of the coating everywhere on the significant surfaces shall conform to the requirements in Tables 1-3 as to
minimum thickness.
NOTE 7—The thickness of electrodeposited coatings varies from point to point on the surface of the product. (See Practice B507.) The thickness is less
in interior corners and holes. Such surfaces are often exempt from thickness requirements. If the full thickness is required in those locations, the
electroplater will have to use special techniques that will probably raise the cost of the process.
NOTE 8—The coating thickness requirement of this specification is a minimum. Variation in the thickness from point to point on an article and from article
to article in a production lot is inherent in electroplating. Therefore, if all of the articles in a production are to meet the thickness requirement, the average
coating thickness for the production lot as a whole will be greater than the specified minimum.
7.4 Adhesion—The coatings shall be adherent to the basis metal when subject to either test, in accordance with 8.5.2 and 8.5.3.
There shall be no separation of the coating from the substrate.
7.5 Integrity of the Coating:
7.5.1 Gross Defects/Mechanical Damage—The coatings shall be free of mechanical damage, large pores, and similar gross
defects. For some applications, this requirement may be relaxed to allow for a small number of such defects (per unit area),
especially if they are outside the significant surfaces.
7.5.2 Porosity—Almost all as-plated electrodeposits contain some porosity. The amount of porosity that may be tolerable depends
on the severity of the environment that the article is likely to encounter during service or storage. If the pores are few in number
or away from significant surfaces, their presence can often be tolerated. Such acceptance (or pass-fail) criteria shall be part of the
product specification for the particular article or coating requiring the porosity test (see 8.6 for porosity test methods).
7.6 Pre-Treatments of Iron and Steel for Reducing the Risk of Hydrogen Embrittlement—Parts that are made of steels with ultimate
tensile strengths of 1000 MPa (hardness of 31 HRC) or greater that have been machined, ground, cold formed, or cold straightened
subsequent to heat treatmentSteel parts having an ultimate tensile strength greater than 1000 MPa (31H RC) 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 prior to processing according to for stress relief 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 pla
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