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GB/T 9799-2024: Metallic and other inorganic coatings - Electroplated coatings of zinc with supplementary treatments on iron or steel
GB/T 9799-2024
GB
NATIONAL STANDARD OF THE
PEOPLE'S REPUBLIC OF CHINA
ICS 25.220.40
CCS A 29
Replacing GB/T 9799-2011
Metallic and other inorganic coatings - Electroplated
coatings of zinc with supplementary treatments on iron or
steel
(ISO 2081.2018, MOD)
ISSUED ON. JUNE 29, 2024
IMPLEMENTED ON. JANUARY 1, 2025
Issued by. State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword... 3
Introduction... 5
1 Scope... 6
2 Normative references... 6
3 Terms and definitions, abbreviations and symbols... 8
3.1 Terms and definitions... 8
3.2 Abbreviations... 8
3.3 Symbols... 8
4 Information that the buyer shall provide to the supplier... 8
4.1 Necessary information... 8
4.2 Additional information... 9
5 Marking... 9
5.1 General rules... 9
5.2 Marking rules... 10
5.3 Marking of base materials... 11
5.4 Marking of heat treatment requirements... 11
6 Requirements... 12
6.1 Appearance... 12
6.2 Thickness... 12
6.3 Trivalent chromium conversion coating and other post-treatment... 13
6.4 Bonding strength of the zinc electroplated coating and the trivalent chromium
conversion coating... 13
6.5 Accelerated corrosion test... 13
6.6 Stress relief heat treatment before electroplating... 14
6.7 Hydrogen embrittlement relief heat treatment... 15
7 Sampling... 15
Appendix A (normative) Marking of chromate conversion coatings and other auxiliary
treatments... 16
Appendix B (normative) Measurement of average coating thickness on small
workpieces... 18
References... 20
Metallic and other inorganic coatings - Electroplated
coatings of zinc with supplementary treatments on iron or
steel
WARNING. Some of the substances and processes required by this document may
cause health hazards if appropriate measures are not taken. This document does
not discuss any matters and regulations that may endanger health, safety or the
environment during the use of this document. Users of this document are
responsible for establishing appropriate and feasible health, safety and
environmental regulations and taking appropriate measures to comply with
relevant national regulations. Compliance with this document does not mean
exemption from legal obligations.
1 Scope
This document specifies the requirements for treated zinc electroplated coatings on steel,
including the information to be provided by the purchaser to the supplier and the
requirements for heat treatment before and after electroplating.
This document does not specify the surface condition of the base metal before zinc
electroplating, but defects on the base metal surface will have an adverse effect on the
appearance and performance of the coating.
This document applies to treated zinc electroplated coatings on iron or steel.
This document does not apply to.
-- zinc electroplated coatings on unformed steel sheets, strips and wires;
-- zinc electroplated coatings for tightly wound springs;
-- zinc electroplated coatings for non-protective decorative purposes.
The thickness of the electroplating coating on threaded parts can be limited by thread
grade or assembly size requirements.
2 Normative references
The provisions of the following documents constitute the essential clauses of this
document through normative references in this text. Among them, for referenced
ISO 15724 Metallic and other inorganic coatings - Electrochemical measurement
of diffusible hydrogen in steels - Barnacle electrode method
3 Terms and definitions, abbreviations and symbols
3.1 Terms and definitions
The terms and definitions defined in GB/T 3138 and GB/T 12334 apply to this
document.
3.2 Abbreviations
The following abbreviations apply to this document.
ER. hydrogen embrittlement relief heat treatment
SR. stress relief heat treatment
T2.organic sealant
3.3 Symbols
The following symbols apply to this document.
Fe. The chemical symbol for iron.
Zn. The chemical symbol for zinc.
4 Information that the buyer shall provide to the supplier
4.1 Necessary information
When ordering electroplated parts according to this document, the purchaser shall
provide the following information in the contract or ordering agreement, or in writing
on the engineering drawing.
a) this document number GB/T 9799 and coating identification (see Chapter 5);
b) the specified principal surfaces, e.g., by marking them on drawings or by
providing samples with appropriate markings;
c) the nature of the base metal, its surface condition and the type of finish (when
these factors may affect the suitability and/or appearance of the electroplated
coating) (see Chapter 1);
d) the locations on the surface where insurmountable defects (hanger marks) are
permitted (see 6.1);
e) the type of finish, e.g., bright, matte or other finish, preferably together with
an approved sample of the finish (see 6.1);
f) the types of chromate conversion coating and other auxiliary treatments (see
6.3 and Appendix A); when the purchaser has special requirements, the
chromate conversion coating shall be canceled, and non-traditional conversion
coating and/or other auxiliary treatments, or paint-like coating treatments may
be applied on the chromate conversion coating;
g) the requirements for thickness and bonding strength tests (see 6.2, 6.4 and
Appendix B);
h) the tensile strength of the workpiece and requirements for heat treatment
before and/or after electroplating (see 6.6 and 6.7);
i) the sampling methods, acceptance levels or other inspection requirements
(when inspection methods different from those specified in GB/T 12609 are
used) (see Chapter 7);
j) the requirements for accelerated corrosion testing (see 6.5) and rating (see
6.5.2).
4.2 Additional information
The purchaser shall provide the supplier with the following additional information.
a) special requirements or restrictions on the pretreatment of the workpiece to be
plated (see [10] and [11] in References);
b) other requirements, such as areas for testing and rating of workpieces of
special shapes.
5 Marking
5.1 General rules
The marking shall appear on the engineering drawing, purchase order, contract or
detailed product description. The marking shall clearly identify, in the following order,
where.
A -- represents bright conversion coating;
Y -- represents one of the other auxiliary treatment coating codes given in Table
A.2.
The chemical symbol of the base metal should be followed by the standard grade of the
special alloy. For example, the UNS number of the special alloy, or the equivalent
national or local number, can be indicated in the symbol < >.
For example, Fe< G43400> is the UNS grade of a high-strength steel (see [12] in
References).
The following are examples of marking.
EXAMPLE 1.The zinc electroplated coating of 12 μm thick on iron or steel (Fe), treated with bright
chemical conversion (A) is marked as.
Electroplated coating GB/T 9799-Fe/Zn12/A
EXAMPLE 2.Same as EXAMPLE 1, but the workpiece is subjected to stress relief heat treatment
before plating, with a minimum duration of 4 hours at 200 °C, marked as SR(200)≥4; for hydrogen
embrittlement relief, it is heat treated at 190 °C for 8 hours after plating (before passivation), marked as
ER(190)8; then, the coating is treated with bright chemical conversion (A) and sealed with an organic
sealant (T2), and it is marked as.
Electroplated coating GB/T 9799-Fe/SR(200)≥4/Zn12/ER(190)8/A/T2
5.3 Marking of base materials
The base material shall be indicated by its chemical symbol. If it is an alloy, the main
component shall be indicated, for example.
a) Fe represents iron or steel;
b) Zn represents zinc alloy;
c) Al represents aluminum and aluminum alloys.
5.4 Marking of heat treatment requirements
Heat treatment requirements shall be marked as follows.
a) The letters SR represent the stress relief heat treatment before electroplating,
and the letters ER represent the hydrogen embrittlement relief heat treatment
after electroplating;
b) The lowest temperature is indicated in degrees Celsius (°C) in parentheses;
c) the duration of heat treatment, in hours (h).
For example, SR(210)1 indicates that the stress relief heat treatment is carried out at
210 °C for 1 hour.
6 Requirements
6.1 Appearance
This document does not specify the condition, finish or roughness of the base material
prior to plating, but the appearance of the electroplated coating will depend on the
surface condition of the base material (see [10] and [11] in References for surface
preparation). The electroplated parts shall not have obvious coating defects such as
blisters, pores, roughness, cracks or local absence of coating on the major surfaces,
except for unavoidable coating defects caused by defects in the base metal. Contact
marks on the workpiece are unavoidable and their location shall be agreed upon by the
interested parties (see 4.1). The workpiece shall be clean and free from damage.
Unless otherwise specified by the purchaser, the appearance of the zinc electroplated
coating shall be bright. If necessary, the purchaser shall provide or confirm samples that
can demonstrate the coating appearance requirements [see 4.1 e)].
6.2 Thickness
The coating thickness indicated in the marking shall be the minimum local thickness.
Unless otherwise specified by the purchaser, the minimum local thickness shall be
measured at any part of the main surface that can be contacted by a ball with a diameter
of 20 mm (see 4.1 and 4.2).
The methods specified in GB/T 6462, GB/T 4955, GB/T 4956, GB/T 11378, GB/T
16921 and GB/T 20018 are applicable to measuring the thickness of various zinc
coatings on steel or iron.
When there is a dispute over the thickness measurement, if the main surface area of the
coating is greater than 100 mm2, it shall be measured according to the method specified
in GB/T 6462; if the main surface area of the coating is less than 100 mm2, the average
thickness of the coating shall be measured according to the method specified in
Appendix B, and the minimum value of the average thickness of the coating can be
regarded as the minimum local thickness of the coating.
Before the thickness is measured according to the method specified in GB/T 4955, a
soft abrasive, such as aluminum oxide grinding paste, shall be used to remove the
chromate conversion coating, other conversion coating or organic coating. When the
conversion coating is thick, the measurement result will be slightly lower.
When the coating is rough or matte, the results obtained by the microscope method (see
GB/T 6462) and the profile measurement method (see GB/T 11378) may be inaccurate.
When being measured by the magnetic method, the thickness value measured for the
rough or matte coating is larger than that for the smooth coating with the same mass per
unit area.
6.3 Trivalent chromium conversion coating and other post-treatment
When the purchaser specifically requests, the trivalent chromium conversion treatment
may be canceled or replaced by other conversion treatments, such as chromium-free or
phosphate conversion [see f) in 4.1]. The codes for trivalent chromium conversion and
all other auxiliary treatments shall comply with the provisions of Appendix A.
6.4 Bonding strength of the zinc electroplated coating and the trivalent chromium
conversion coating
When the friction polishing test is carried out in accordance with GB/T 5270, the zinc
electroplated coating shall continuously adhere to the base metal. The chromate
conversion coating shall be subjected to the bonding strength test in accordance with
the relevant provisions of GB/T 9791.
All tests except the thickness test shall be carried out 24 hours after chromate
conversion treatment.
6.5 Accelerated corrosion test
6.5.1 Neutral salt spray test
The neutral salt spray test (NSS) specified in GB/T 10125 shall be carried out for the
time specified in Table 1.The test surface shall be free of white rust and red rust when
observed with the naked eye or corrected vision. Slight staining shall not be a reason
for rejection.
Some coating marks in Table 1 give the minimum local thickness of the zinc
electroplated coating after chromate treatment under various service conditions. To
ensure corrosion resistance, the thickness requirement of the coating depends on the
severity of the service conditions. For example, the coating marked with Fe/Zn5 is only
of the heat treatment process shall be indicated in the mark in accordance with the
provisions of 5.2, 5.3 and 5.4.
Steel parts with scale or dirt shall be cleaned before electroplating. For high-strength
steel (tensile strength greater than or equal to 1000 MPa), chemical alkaline degreasing,
anodic electrolytic degreasing or mechanical degreasing shall be used to avoid
hydrogen embrittlement during the cleaning process (see [10] in References).
6.7 Hydrogen embrittlement relief heat treatment
Steel parts with a maximum tensile strength greater than or equal to 1000 MPa and
surface-hardened workpieces shall be heat treated to reduce hydrogen embrittlement.
The heat treatment process and grade shall be in accordance with GB/T 19350 or as
specified by the purchaser.
When heat treatment for stress relief before electroplating or for hydrogen
embrittlement relief after electroplating is specified (see 6.6), the time and temperature
of the heat treatment process shall be marked in the mark, as shown in 5.4.Unless
otherwise specified by the purchaser, the actual effect of the hydrogen embrittlement
relief heat treatment shall be measured as follows. the threaded parts shall be subjected
to residual hydrogen embrittlement test in accordance with GB/T 26107 or GB/T
3098.17; the relative dissolved hydrogen concentration in the steel shall be measured
in accordance with ISO 15724.
7 Sampling
The number of samples specified in GB/T 12609 shall be randomly selected from the
inspection batch. The wor...