GB/T 13913-2008Metallic coatings -- Autocatalytic (Electroless) nickel-phosphorus alloy coatings -- Specification and test methods (English PDF)

4.1 Necessary information

When the ordered workpiece needs to be plated in accordance with the requirements of this standard, the purchaser shall use the contract as a written form in the engineering drawing, purchaser's purchase order and details.

The detailed production schedule provides the following information for all important items.

a) Coating name (see Chapter 5).

b) Tensile strength of the part and any heat treatment requirements before and after coating deposition (see 6.2, 6.9, 6.10, 6.11, 6.12 and the appendix A).

c) Detailing of the major surfaces with appropriate markings on drawings or specimens.

d) The nature, condition and surface roughness of the base metal, if any of these factors will affect the serviceability or Appearance (see 6.2).

e) The location, type and size of defects, such as creases, allowed defects (see 6.2).

f) Surface roughness requirements, such as bright, dull, glossy or other surface roughness requirements, and provide the expected surface roughness as much as possible sample. Remember that samples that have been tested for surface roughness will lose their effectiveness over time and will therefore need to be replaced regularly sample.

g) any requirements for the underlying layer (see 6.17).

h) Sampling methods, acceptance criteria or other inspection requirements. If it differs from the requirements already given in GB/T 12609 (see Chapter 7).

i) Standard methods for testing thickness, hardness, bonding strength, porosity, corrosion resistance, wear resistance and weldability (see 6.4, 6.5, 6.6, 6.7, 6.8, 6.13, 6.14 and Appendix B) and special test conditions (see 6.1).

j) Any special requirements for treatments that produce compressive stress, such as shot peening before plating (see 6.16).

k) Special requirements for pretreatment or limited pretreatment.

1) Special requirements for heat treatment or restrictions on heat treatment.

m) Special requirements for maximum coating thickness, especially for parts that are worn or over-processed. Whether before parts are plated or the thickness is measured after plating, and these requirements must be strictly followed.

n) Special requirements for coating (plating) layers on electroless nickel-phosphorus plating.

4.2 Supplementary information

The following supplementary information shall be specified by the purchaser.

a) Steel parts should be demagnetized (demagnetized) before plating to minimize the entry of magnetic particles or iron filings into the coating;

b) Final surface roughness of the coating (see 6.3);

c) Any special requirements for the chemical composition of the coating (see 6.15);

d) Any special requirements for the repair of non-conforming products;

e) Any other special requirements.

5.1 Overview

Base metal, coating and heat treatment conditions should be noted on engineering drawings, purchase orders, contracts or product schedules. The identification should be in the following order Conduct. base metal, special alloy (optional), internal stress relief requirements, thickness and type of bottom layer, phosphorus content in electroless nickel-phosphorus plating and coating thickness, the type and thickness of the coating (plating) layer applied on the electroless nickel-phosphorus plating layer and post-treatment (including heat treatment). Double slash (//) Will be used to indicate that a step or operation is not listed or omitted.

The logo includes the following.

a) The term "electroless nickel-phosphorus plating";

b) National standard number, namely. GB/T 13913;

c) hyphen;

d) Chemical symbol of the base metal (see 5.2);

e) Slash separator (/);

f) Symbols for electroless nickel-phosphorus plating (see 5.4), and symbols for coatings before and after electroless nickel-phosphorus plating (see 5.4), plating sequence each level in is separated by delimiters in order of operations. The marking of the coating should include the thickness of the coating (µm) and heat treatment requirements (See 5.3).

5.2 Identification of base metal

The base metal should be identified by its chemical symbol or, in the case of an alloy, by its main composition.

For special alloys, it is recommended to identify them by their standard names. For example. fill in the steel number or corresponding national standard in the symbol. like Fe<16Mn>is the national standard naming for low alloy high strength steel.

NOTE. In order to ensure proper surface preparation and therefore bonding between coating and substrate, it is extremely important to determine the specific alloy and its metallurgical state.

important.

5.3 Identification of heat treatment requirements

Heat treatment requirements shall be marked in square brackets as follows.

a) SR means stress-relieving heat treatment;

HT means heat treatment to increase the hardness of the coating or the bonding force between the coating and the base metal;

ER stands for heat treatment to eliminate hydrogen embrittlement.

b) Indicate the minimum temperature during heat treatment (°C) in parentheses.

c) Mark the duration of heat treatment (h).

Example. Stress-relieving heat treatment is performed at 210°C for 1 hour, and its mark is. [SR (210) 1]

5.4 Identification of coating type and thickness

Electroless nickel-phosphorus plating should be identified with the symbol NiP, and fill in the value of the phosphorus content of the coating in the parentheses immediately following it, and then Subsequently, the minimum local thickness of the electroless nickel-phosphorus plating layer is marked, in µm.

The bottom layer should be identified by the chemical symbol of the deposited metal, followed by the minimum local thickness of the coating in µm (see 6.17). For example, the symbol Ni represents nickel plating.

Other coatings, such as chromium, deposited over electroless nickel-phosphorus plating. The identification method is the chemical symbol of the electroplating layer plus the minimum size of the plating layer.

Partial thickness, unit is µm (see 6.17).

5.5 Examples of identification

a) Electroless plating of a nickel-phosphorus coating with a phosphorus content of 10% (mass fraction) and a thickness of 15 µm on a 16Mn steel substrate requires a temperature of 210°C.

A stress-relieving heat treatment was performed for 22 hours at high temperature, and then 0.5 µm thick chromium was electroplated on the surface. After chromium plating, then heat it at 210°C Heat treatment to eliminate hydrogen embrittlement is carried out for 22 hours at high temperature. The specific identification is as follows.

Electroless nickel-phosphorus plating GB/T 13913-Fe<16Mn>[SR(210)22]/NiP(10)15/Cr0.5[ER(210)22]

b) The same coating as a) is plated on the aluminum alloy substrate without heat treatment requirements. The specific markings are as follows.

Electroless nickel-phosphorus plating GB/T 13913-Al<2B12>//NiP(10)15/Cr0.5//

c) The same coating as a) is plated on the copper alloy substrate without heat treatment requirements. The specific markings are as follows.

Electroless nickel-phosphorus plating GB/T 13913-Cu<H68>//NiP(10)15/Cr0.5//Due to the order, the product details include not only the contents of the logo, but also the clarity of other important requirements listed in Chapter 4.

illustrate.

6.1 Alternative specimens

When the size, shape or material of the plated workpiece is not suitable for testing, or when the plated workpiece is not available due to too few quantities or high price.

When destructive testing is suitable, surrogate specimens can be used to measure the bonding strength, thickness, porosity, corrosion resistance, hardness and other properties of the coating.

nature. The metallurgical condition and surface quality of the material selected for the replacement sample should be consistent with that of the plated workpiece. And should also take and plated work the same processing technology.

Substitute test specimens may be used to determine whether plated workpieces meet the requirements of this standard. The number, material, shape and the size should be specified by the buyer.

6.2 Appearance

The appearance of important surfaces of electroless nickel-phosphorus plating shall be bright, semi-bright or matte as specified by the purchaser. and inspect with the naked eye the surface shall be free of pits, blisters, flaking, ball growths, cracks and other defects that would compromise the final finish (unless otherwise required). combine Specimens of the grid will be used for comparative testing.

Plating defects and variations caused by base metal surface defects (such as scratches, pores, rolling marks, inclusions), and in strict compliance with Defects that remain in the final finish after complying with the prescribed metal finishing operations are not causes of scrap. The purchaser should specify the added Limits of defects tolerable on the surface of workmanship and unprocessed products. However, damaged base metal cannot be used for plating.

Blisters or cracks visible to the naked eye, as well as defects caused by heat treatment, should be considered rejects.

Note. Defects that already exist on the base metal before plating, including hidden defects, will be reappeared after plating. In addition, post-plating heat treatment will produce stains and Colored oxides. However, the production of colored oxides should not be considered a cause of scrap unless heat treatment is carried out in a specified special atmosphere. right the purchaser without objection may consider accepting such defects.

6.3 Surface roughness

If the purchaser specifies final surface roughness requirements, the measurement method shall comply with the provisions of GB/T 10610.

Note. The final surface roughness of the electroless nickel-phosphorus plating is not necessarily better than the surface roughness of the substrate before plating. Unless the bottom layer of the coating is particularly smooth and polished.

6.4 Thickness

The coating thickness specified in the marking section refers to its minimum local thickness. Unless otherwise specified by the purchaser, the minimum thickness of the coating the internal thickness should be measured at any point on the important surface of the workpiece (which can be tangent to a ball with a diameter of 20mm).

See Appendix C for requirements on anti-corrosion coating thickness under different conditions of use. The thickness measurement method is selected from Appendix B.

6.5 Hardness

If a hardness value is specified, it should be measured according to the method specified in GB/T 9790.The hardness of the coating should be within the hardness value specified by the purchaser.

Within ±10%.

6.6 Bonding force

Electroless nickel-phosphorus plating can be attached to both plated and unplated metals. According to the purchaser's specifications, the coating shall be able to pass One or more binding force tests specified in GB/T 5270.

6.7 Porosity

If required, the maximum porosity of the electroless nickel-phosphorus coating shall be determined based on the purchaser's specifications and the porosity test method.

6.8 Corrosion resistance of coating

If required, the corrosion resistance of the coating and its test method shall be specified by the purchaser in accordance with standards consistent with GB/T 6461.

Methods such as GB/T 10125, acetate salt spray test and copper accelerated salt spray test can be specified as tests to evaluate the resistance of coatings to pitting corrosion.

method.

Note. Corrosion resistance testing in artificial environments does not involve the service life of the workpiece or the performance of the workpiece.

6.9 Heat treatment to eliminate internal stress before plating

When specifically specified by the purchaser [see 4.1b)], the tensile strength is greater than or equal to 1000MPa, and the tensile strength is Steel parts that produce tensile stress due to processing require heat treatment to eliminate internal stress before cleaning and metal deposition. Heat to eliminate internal stress the processing procedures and types should be specifically specified by the purchaser. Or the purchaser can choose the appropriate process and type in accordance with GB/T 19349.Eliminate internal stress the heat treatment step should be performed before any acidic or cathodic electrolysis.

Note. Oxide or scale on steel must be removed before plating. For high-strength steel, in order to avoid hydrogen embrittlement, priority should be given to selecting Non-electrolytic alkaline and anodic alkaline cleaning methods as well as mechanical cleaning methods.

6.10 Heat treatment to eliminate hydrogen embrittlement after plating

Steel parts with a tensile strength greater than or equal to 1000MPa, like workpieces that have been surface hardened, need to be treated according to the requirements after plating.

GB/T 19350 or relevant processes specified by the purchaser, and heat treatment to eliminate hydrogen embrittlement [see 4.1b)].

All heat treatments to eliminate hydrogen embrittlement after plating should be carried out promptly, preferably after surface finishing and before grinding and other machining.

Complete within 1 hour, no more than 3 hours.

The effectiveness of hydrogen embrittlement elimination treatments shall be determined by test methods specified by the purchaser or by test methods described in relevant standards. like ISO 10587 describes a method for testing residual stress hydrogen embrittlement in threaded parts, while ISO 15724 describes the concentration of diffusible hydrogen in steel.

a testing method.

Note. Heat treatment according to the procedures specified in GB/T 19350 cannot completely eliminate hydrogen embrittlement. Whenever possible, the test test for residual hydrogen embrittlement should be specifically pointed out.

test. Eliminating hydrogen embrittlement of the test sample can illustrate the effectiveness of the heat treatment process for eliminating hydrogen embrittlement. But these all depend on the number of test samples taken.

6.11 Heat treatment to increase hardness

The regulations for using heat treatment methods to improve the hardness and wear resistance of electroless nickel-phosphorus plating are shown in Table A. 1 (see 6.13).

If necessary, heat treatment to improve the hardness and wear resistance of the electroless nickel-phosphorus coating should be completed within 1 hour after plating, and should be performed before machining.

carried out before. The duration of heat treatment shall be at least 1 h after the parts reach the specified heat treatment temperature.

If the heat treatment process to increase the hardness of the coating meets the requirements specified in GB/T 19350, then there is no need to separately Perform heat treatment to eliminate hydrogen embrittlement.

6.12 Heat treatment to improve bonding strength

The heat treatment process to improve the bonding strength of electroless nickel-phosphorus plating on a certain metal substrate should refer to Table A. 1, unless the buyer specifically Additional process requirements are specified.

6.13 Wear resistance

If required, the purchaser shall specify the requirements for the coating's wear resistance and specify the test used to detect whether the coating's wear resistance meets the requirements.

method.

Note. The wear resistance of electroless nickel-phosphorus plating will be affected by heat treatment (see 6.11 and Appendix A).

6.14 Solderability

If required, the purchaser shall specify the solderability of the coating and specify the test used to detect whether the solderability of the coating meets the requirements.

method.

Note. In order to minimize the possibility of corrosion during welding (especially electronic products), phosphorus plating with more than 10% (mass fraction) is sometimes used.

It is more common to use plating layers with less phosphorus content (1% to 3% mass fraction) for welding.

6.15 Chemical composition

The phosphorus content in electroless nickel-phosphorus coatings shall be specified in the marking (see 5.4 and Table C.2). When carried out according to the method provided in Appendix D when measuring, the error between the measured phosphorus content and the required phosphorus content should not exceed ±0.5%. If the phosphorus content is not specified, then the phosphorus content will be in the range of 1% to 14% (mass fraction) (unless there are other requirements) [see 4.2c)].

6.16 Shot peening of metal parts

If the purchaser requires shot peening prior to plating, the shot peening procedure shall be preceded by any acidic or alkaline electrolytic treatment in accordance with in accordance with the requirements of GB/T 20015.The standard also specifies methods for measuring shot peening intensity.

Note. Shot peening before plating can minimize the reduction in fatigue strength and bonding strength after electroless nickel-phosphorus plating is applied to high-strength steel. for that it is recommended that some workpieces that are often used in repetitive and complex load-bearing patterns be shot peened before plating. Other factors that affect fatigue strength include plating layer thickness. The coating should be as thin as possible while meeting the intended use conditions. The compressive stress produced by controlled shot peening can not only improve it has high corrosion resistance and stress corrosion crack propagation resistance, and is also beneficial for improving the bonding strength of the coating.

6.17 Bottom layer and surface layer

The bottom layer of electroplated nickel should comply with the relevant regulations in GB/T 12332 [see 4.1g)]. Chromium plating used over electroless nickel-phosphorus plating should Comply with relevant regulations in GB/T 11379.

Note. Electroplating a 2µm~5µm thick nickel bottom layer can be used for base metals containing antimony, arsenic, bismuth, copper, lead or tin (except brass and bronze).

Electroplating a 2µm~5µm thick nickel or copper bottom layer can be used for base metals containing trace amounts of magnesium and zinc.

A nickel layer can be flash-plated between the copper base layer and the electroless nickel-phosphorus plating.

Electroplating a 1µm~2µm thick nickel bottom layer can be used for base metals containing trace amounts of chromium, lead, molybdenum, nickel, tin, titanium or tungsten.

The purpose of electroplating the bottom layer is to reduce the fouling hazard of elements that will reduce the deposition efficiency during the deposition process. In addition, electroplated metal the bottom layer prevents the diffusion of impurities from the base metal into the electroless nickel-phosphorus plating layer and helps improve bonding strength.