Metallic and other inorganic coatings—Chromate-free chemical conversion coatings on allumion and its alloys
Some standard content:
ICS25.220.20
National Standard of the People's Republic of China
GB/T39495—2020
Metallic and other inorganic coatings
Chromate-free chemical conversion coatings onallumionanditsalloys2020-11-19 Issued
State Administration for Market Regulation
National Standardization Administration
Issued
2021-10-01Implementation
Foreword
This standard was drafted in accordance with the provisions given in GB/T1.1-2009. This standard was proposed by the China Machinery Industry Federation. This standard is under the jurisdiction of the National Technical Committee for Standardization of Metallic and Non-metallic Coatings (SAC/TC57). GB/T39495—2020
The drafting units of this standard are: Wuhan Institute of Material Protection Co., Ltd., Zhuhai Aomelun Fine Chemical Co., Ltd., Hefei Huaqing Fangxing Surface Technology Co., Ltd., Guangzhou Sanfu New Material Technology Co., Ltd., Wuhan Institute of Standardization, and the main drafters of this standard are: Zhang Dezhong, Mao Zuguo, Jia Jianxin, Ao Zhonghua, Liu Wanqing, He Yuan, Tian Zhibin, Zhan Yiteng, Huang Qing, Huang Yong, Yi Juan, Zhao Tao, Zhang Qi.
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GB/T39495—2020
Introduction
The chemical conversion of aluminum and aluminum alloys is divided into chromate chemical conversion (hexavalent chromium, trivalent chromium) and chromium-free chemical conversion. The chromate chemical conversion process is simple, the conversion film has excellent performance, and it is widely used. However, since the chromium ions (especially hexavalent chromium) in the conversion solution are carcinogenic, they affect the health of the workers and the waste liquid pollutes the environment. It has become a trend to find a chromium-free chemical conversion process to replace the chromate chemical conversion. According to the main components of the conversion solution, chromium-free conversions include: water oxidation, zirconium salt conversion, titanium salt conversion, rare earth metal salt conversion, permanganate conversion, molybdate conversion, silicate conversion, cobalt salt conversion, lithium salt conversion, phosphate conversion, silane conversion, etc. In order to improve the performance of the conversion film, a composite conversion system of two or more of the above components is introduced, such as titanium-zirconium system, titanium-cobalt system, and titanium-silane system. With the introduction of many new conversion liquid formulas and the development of engineering applications, it is urgent to formulate technical standards to specify the requirements of chromium-free chemical conversion films and test methods to verify whether the film layer meets the requirements. 1 Scope
Metal and other inorganic coatings
Aluminum and aluminum alloy chromium-free chemical conversion film
GB/T39495—2020
This standard specifies the classification, requirements and test methods of water-washable and no-wash chromium-free chemical conversion films for aluminum and aluminum alloys, as well as sampling inspection procedures. This standard applies to chromium-free chemical conversion films for extruded aluminum and aluminum alloy parts, profiles, coils, plates and cast aluminum alloy parts. Chromium-free chemical conversion films can be used as anti-corrosion layers alone or as the bottom layer of organic coatings (such as coatings, rubbers, adhesives). Normative references
The following documents are essential for the application of this document. For all dated references, only the dated version applies to this document. For any undated referenced document, the latest version (including all amendments) applies to this document. Terminology for surface treatment of metals and other inorganic coatings GB/T3138
GB/T6461 Rating of samples and test pieces of metals and other inorganic coatings on metal substrates after corrosion tests GB/T9286 Cross-cut test for paint and varnish films GB/T10125 Artificial atmosphere corrosion test Salt spray test 9 Sampling procedure for counting inspection of electrodeposited metal coatings and related finishes GB/T12609
GB/T20017
Determination of mass per unit area of ??metals and other inorganic coatings Review of gravimetric and chemical analysis methods QJ1827 Test method for contact resistance of low-resistance metal coatings and chemical conversion films 3 Terms and definitions
The terms and definitions defined in GB/T3138 and the following terms and definitions apply to this document. 3.1
Conversion coating
conversion coating
Surface coating containing base metal compounds formed by chemical or electrochemical processes. 3.2
chemical conversion coating
Chemical conversion coating
Surface coating containing base metal compounds formed by chemical reaction between base metal and conversion liquid. 3.3
Chromium-free chemical conversion coating Chemical conversion coating formed by conversion liquid that does not contain chromium (hexavalent or trivalent). 3.4
rinsed chromium-free chemical conversion coating Chromium-free chemical conversion coating After conversion treatment, it needs to be washed with water and then dried. Note: This type of conversion coating is generally used for extruded aluminum products and cast aluminum parts. 3.5
non-rinsed chromium-free chemical conversion coating
After conversion treatment, the chromium-free chemical conversion coating does not need to be washed and can be dried directly. Note 1: This special conversion coating is generally used for thin aluminum plates that are immediately painted or coated with adhesives. Note 2: Non-rinsed conversion coatings are being studied for more welded parts and castings. KaeerKAca-
GB/T39495—2020
4 Information that the purchaser should provide to the supplier
Necessary information
The purchaser should provide the supplier with the following written information on the order, contract or engineering drawing: a)
The main surface of the workpiece, for example, marked with size range on the drawing or providing samples with appropriate markings; the nature, state, finishing and surface roughness of aluminum and aluminum alloys (when they may affect the performance and/or appearance of the conversion film); the location of any unavoidable defects, such as hanger marks; the required surface color, such as colorless, light yellow or other types, it is best to provide samples confirmed by both parties; if different from the provisions of this standard, the sampling method, acceptance criteria and other inspection requirements should be specified; the requirements for unit area quality, the measurement location should be marked on the drawing: adhesion requirements and their test methods;
contact resistance requirements;
corrosion resistance requirements.
Additional information
When necessary, the purchaser may provide the following additional information in writing on the contract, order or engineering drawing: a)
Specific composition of the elemental composition and impurities of the conversion coating; b))
Special cleaning process required to be used;
5 Classification
Special requirements for the substrate;
Weldability requirements and test methods;
Abrasion resistance requirements and test methods;
Other requirements.
5.1 Overview
According to the application and performance requirements, chromium-free conversion coatings are classified. 2 Types
Table 1 shows the types of chromium-free chemical conversion coatings. Table 1 Types of chromium-free chemical conversion coatings
Types
6 Surface pretreatment
Purpose and corrosion resistance
As an anticorrosion layer alone, it provides the product with maximum corrosion protection performance Moderate corrosion protection performance, as a base for coatings, and also used in combination with rubber Decorative, low corrosion resistance, low contact resistance Although this standard does not specify the state, finish or surface roughness of the substrate before conversion treatment, the appearance and performance of the chromium-free conversion film depend on the state of the substrate. It is necessary for the purchaser to specify the finish and surface roughness of the substrate so that the performance of the conversion film meets the product requirements The parts of the aluminum and aluminum alloy surfaces that need to be prepared with conversion films should be cleaned, derusted, descaled, and metal chips, grinding powder, oil, grease, lubricating oil, fingerprints or other contaminants that affect the preparation of conversion films should be removed. Surface pretreatment should be done with a chrome-free cleaning agent. Parts of the aluminum and aluminum alloy surfaces that do not require conversion coating should be treated with protective treatment. 7 Chrome-free chemical conversion treatment
7.1 Conversion solution
The conversion solution does not contain chromium (including hexavalent chromium and trivalent chromium), is usually acidic, and may contain other different salts. These salts have different degrees of influence on the appearance and performance of the conversion film. The performance of the conversion film is determined by the composition of the conversion solution, pH value, temperature, conversion time, and the properties and surface state of the aluminum alloy. The conversion solution should not be turbid or produce insoluble matter, and should be maintained as required, and the aging tank solution should be replaced in time. 7.2 Treatment method
Usually, the immersion method is adopted, and spraying, brushing, roller coating or coating can also be adopted. When these treatment methods are adopted, they must be strictly followed in accordance with the process operation specifications.
7.3 Water washing
If the conversion film is used as the bottom layer of other covering layers, it should be washed with deionized water with a conductivity of less than 100μS/cm. If necessary, it can be washed with hot water
If it is directly dried after conversion treatment and used as the coating bottom layer without affecting the coating performance, it can be washed without water. If all or part of the conversion film is used as a corrosion-resistant coating or decorative layer, it should be fully washed with water after conversion treatment to remove any contaminants remaining on the surface.
7.4 Drying
Water-washed and no-clean conversion coatings should be dried. Drying temperature may affect the corrosion resistance of the conversion coating. Therefore, the drying of the conversion coating should meet the requirements of subsequent processes.
8 Requirements and test methods
8.1 Substitute specimens
When the conversion coating workpiece is not suitable for testing, or the number of conversion coating workpieces is small or the value is high and it cannot be submitted for destructive testing, substitute specimens can be used to measure adhesion, unit area mass, corrosion resistance and other properties. Substitute specimens should have the same alloy composition and surface state as the workpiece they represent, and should be converted together with the workpiece. The purchaser should clearly specify the method of using substitute specimens and the number, material, shape and size of substitute specimens used. 8.2 Appearance
The conversion coating on the main surface should be uniform and consistent, and no defects such as roughness, powdering, flow marks, bubbles, inclusions, depressions, dark spots, pinholes, scratches, scratches, etc. and any damage to the substrate are allowed. Chromium-free chemical conversion coatings are usually colorless to the naked eye or corrected vision. The specific appearance and color requirements can be determined by the supplier and the buyer through standard samples.
nKaeerKAca-
GB/T39495—2020
Defects caused by the surface state of the substrate or defects that still exist under normal operation shall not be rejected. The buyer shall specify the acceptance limit of substrate defects.
3 Unit area mass
The unit area mass of the conversion film shall be measured in accordance with GB/T20017. 8.4
Adhesion
The conversion film shall adhere to the surface of the substrate and be free of powder. At present, there is no effective method to directly measure the adhesion of chromium-free conversion films on aluminum and aluminum alloys. When the conversion film is used as a coating base, the practical method is to measure the adhesion of another layer of organic film coated on the conversion film to evaluate the adhesion of the conversion film. If there is no special provision, the adhesion of the paint film on the conversion film shall be measured in accordance with GB/T9286. 8.5
5 Contact resistance
If there is a requirement for contact resistance, the contact resistance of the conversion coating shall be measured in accordance with QJ1827. For the convenience of use of this standard, the measurement method of QJ1827 is shown in Appendix A. If required, the maximum resistance value and test frequency shall be agreed upon by the supplier and the buyer. 8.6
Corrosion resistance
Corrosion resistance shall be subjected to a neutral salt spray test (NSS test) in accordance with GB/T10125. The samples shall be rated in accordance with GB/T6461. 9 Sampling and inspection
Unless otherwise specified, samples shall be randomly selected from the inspection lot in accordance with the sample size specified in GB/T12609. The workpieces in the sample shall be checked to confirm whether they meet the requirements of this standard. The inspection lot shall be judged to meet or not meet each requirement in accordance with the sampling inspection procedure of GB/T12609.
Do not touch the surface of the sample within 24 hours after the conversion treatment, and any test shall be carried out after 24 hours. 4
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A.1 Overview
Appendix A
(Informative Appendix)
Contact resistance measurement method
GB/T39495—2020
When the aluminum material after chromium-free conversion is used for the surface protection of spacecraft, electronic appliances and some instruments, its contact resistance is a very important characteristic parameter, so it is necessary to measure the contact resistance of the chromium-free chemical conversion film. In addition to the unit area mass of the film layer and the structure of the film, the factors affecting the contact resistance value are also related to the cleanliness, flatness, and pressure applied to the contact electrode of the film surface and the electrode surface. There are generally two methods for measuring contact resistance: the bridge method and the voltammetric method. The former has high measurement accuracy but the measurement process is cumbersome and is suitable for laboratory applications. The latter is convenient to measure and the measurement results can meet the requirements. A.2 Measurement method (QJ1827)
A.2.1 Principle
Based on Ohm's law R=U/I, that is, under constant current, a constant pressure load is applied between two electrodes of a certain area, and the voltage drop between the electrodes is measured with a microvoltmeter, and the contact resistance is calculated according to Ohm's law. See Figure A.1 for the schematic diagram. +12V
Stable mains
220 V
A.2.2 Measuring instrument
Stable voltage source
Stable intermediate source
Figure A.1
Instrument model: FCE-1 contact resistance tester; Instrument resolution: ±0.0012;
Electrode: Gold-plated electrode with a tip of 5cm2. A.2.3 Sample
The sample should be the same material as the workpiece and processed at the same time. +ay
Micro-manipulator
Upper plate
Lower outlet
Test piecebzxz.net
Schematic diagram of contact resistance measurement principle
rKaeerKAca-
Work
Zero
Press digital pressure meter
GB/T39495—2020
The surface of the sample should be flat, without burrs, scratches and other defects, and the surface roughness should be less than 0.8um. ??The size is 250mm×76mm×1mm aluminum plate, divided into 10 squares (see Figure A.2). 30
A.2.4 Measurement
A.2.4.1
×38=190
Figure A.2 Sample grid division
Turn on the power of the measuring instrument.
Turn the button to the zeroing position, adjust the zeroing knob, and make the digital display read zero. A.2.4.2
Turn the button to the working position,
A.2.4.3
Unit is millimeter
A.2.4.4 Wipe the electrode contact surface with a cotton ball soaked in anhydrous ethanol. Move the electrode to make the upper and lower electrodes contact, and then pressurize until the pressure gauge reads 165×10*Pa. The contact resistance value between the two levels should be zero. If it is not zero, it indicates that there is dirt on the end surface of the electrode. The electrode should be cleaned again and its resistance value should be measured again.
A.2.4.5 After unloading, place the cleaned test piece flat on the lower electrode, put down the upper electrode, pressurize until the pressure gauge reads 165×101Pa, and measure the resistance value of each square in turn. During the test, the edge of the test piece cannot touch any part of the instrument. Calculation of results
A.2.5
The contact resistance value of the test piece is the arithmetic mean of the contact resistance values ??of 10 squares, and the calculation formula is: Ri
Where:
R.,R,R.
Ri+R+R,++R
The contact resistance value of the test piece, in ohm (2); -The contact resistance value measured by 10 squares, in ohm (2). rKaeerKAca-1 Substitute Specimens
When the conversion coated workpiece is not suitable for testing, or the number of conversion coated workpieces is small or the value is too high to be submitted for destructive testing, substitute specimens can be used to measure adhesion, mass per unit area, corrosion resistance and other properties. Substitute specimens should have the same alloy composition and surface state as the workpiece they represent, and should be converted together with the workpiece. The purchaser should clearly specify the method of using substitute specimens and the number, material, shape and size of substitute specimens used. 8.2 Appearance
The conversion film on the main surface should be uniform and consistent, and no defects such as roughness, powdering, flow marks, blistering, inclusions, depressions, dark spots, pinholes, and scratches, scratches, and any damage to the substrate are allowed. Chromium-free chemical conversion films are usually colorless under the naked eye or corrected vision. The specific appearance and color requirements can be determined by the supply and demand parties through standard samples.
nKaeerKAca-
GB/T39495—2020
Defects caused by the surface condition of the substrate or defects that still exist under normal operation shall not be rejected. The purchaser shall specify the acceptance limit of substrate defects.
3 Unit area mass
The unit area mass of the conversion film shall be measured in accordance with GB/T20017. 8.4
Adhesion
The conversion film shall adhere to the surface of the substrate and be free of powder. At present, there is no effective method to directly measure the adhesion of chromium-free conversion films on aluminum and aluminum alloys. When the conversion film is used as a coating base, the practical method is to measure the adhesion of another layer of organic film coated on the conversion film to evaluate the adhesion of the conversion film. If there is no special provision, the adhesion of the paint film on the conversion film shall be measured in accordance with GB/T9286. 8.5
5 Contact resistance
If there is a requirement for contact resistance, the contact resistance of the conversion film shall be measured according to QJ1827. For the convenience of using this standard, the measurement method of QJ1827 is shown in Appendix A. If required, the maximum resistance value and test frequency shall be agreed upon by the supplier and the buyer. 8.6
Corrosion resistance
Corrosion resistance shall be subjected to neutral salt spray test (NSS test) in accordance with GB/T10125. The samples shall be rated in accordance with GB/T6461. 9 Sampling and inspection
Unless otherwise specified, samples shall be randomly selected from the inspection batch according to the sample quantity specified in GB/T12609. Check the workpieces in the sample to confirm whether they meet the requirements of this standard. The inspection batch shall be judged to meet or not meet each requirement according to the sampling inspection procedure of GB/T12609.
Do not touch the surface of the sample within 24 hours after the conversion treatment, and any test shall be carried out after 24 hours. 4
rrKaerKAca-
A.1 Overview
Appendix A
(Informative Appendix)
Contact resistance measurement method
GB/T39495—2020
When the aluminum material after chromium-free conversion is used for the surface protection of spacecraft, electronic appliances and some instruments, its contact resistance is a very important characteristic parameter, so it is necessary to measure the contact resistance of the chromium-free chemical conversion film. In addition to the unit area mass of the film layer and the structure of the film, the factors affecting the contact resistance value are also related to the cleanliness, flatness, and pressure applied to the contact electrode of the film surface and the electrode surface. There are generally two methods for measuring contact resistance: the bridge method and the voltammetric method. The former has high measurement accuracy but the measurement process is cumbersome and is suitable for laboratory applications. The latter is convenient to measure and the measurement results can meet the requirements. A.2 Measurement method (QJ1827)
A.2.1 Principle
Based on Ohm's law R=U/I, that is, under constant current, a constant pressure load is applied between two electrodes of a certain area, and the voltage drop between the electrodes is measured with a microvoltmeter, and the contact resistance is calculated according to Ohm's law. See Figure A.1 for the schematic diagram. +12V
Stable mains
220 V
A.2.2 Measuring instrument
Stable voltage source
Stable intermediate source
Figure A.1
Instrument model: FCE-1 contact resistance tester; Instrument resolution: ±0.0012;
Electrode: Gold-plated electrode with a tip of 5cm2. A.2.3 Sample
The sample should be the same material as the workpiece and processed at the same time. +ay
Micro-manipulator
Upper plate
Lower outlet
Test piece
Schematic diagram of contact resistance measurement principle
rKaeerKAca-
Work
Zero
Press digital pressure meter
GB/T39495—2020
The surface of the sample should be flat, without burrs, scratches and other defects, and the surface roughness should be less than 0.8um. ??The size is 250mm×76mm×1mm aluminum plate, divided into 10 squares (see Figure A.2). 30
A.2.4 Measurement
A.2.4.1
×38=190
Figure A.2 Sample grid division
Turn on the power of the measuring instrument.
Turn the button to the zeroing position, adjust the zeroing knob, and make the digital display read zero. A.2.4.2
Turn the button to the working position,
A.2.4.3
Unit is millimeter
A.2.4.4 Wipe the electrode contact surface with a cotton ball soaked in anhydrous ethanol. Move the electrode to make the upper and lower electrodes contact, and then pressurize until the pressure gauge reads 165×10*Pa. The contact resistance between the two levels should be zero. If it is not zero, it indicates that there is dirt on the end surface of the electrode. The electrode should be cleaned again and its resistance value should be measured again.
A.2.4.5 After unloading, place the cleaned test piece flat on the lower electrode, put down the upper electrode, pressurize until the pressure gauge reads 165×101Pa, and measure the resistance value of each square in turn. During the test, the edge of the test piece cannot touch any part of the instrument. Calculation of results
A.2.5
The contact resistance value of the test piece is the arithmetic mean of the contact resistance values ??of 10 squares, and the calculation formula is: Ri
Where:
R.,R,R.
Ri+R+R,++R
The contact resistance value of the test piece, in ohm (2); -The contact resistance value measured by 10 squares, in ohm (2). rKaeerKAca-1 Substitute Specimens
When the conversion coated workpiece is not suitable for testing, or the number of conversion coated workpieces is small or the value is too high to be submitted for destructive testing, substitute specimens can be used to measure adhesion, mass per unit area, corrosion resistance and other properties. Substitute specimens should have the same alloy composition and surface state as the workpiece they represent, and should be converted together with the workpiece. The purchaser should clearly specify the method of using substitute specimens and the number, material, shape and size of substitute specimens used. 8.2 Appearance
The conversion film on the main surface should be uniform and consistent, and no defects such as roughness, powdering, flow marks, blistering, inclusions, depressions, dark spots, pinholes, and scratches, scratches, and any damage to the substrate are allowed. Chromium-free chemical conversion films are usually colorless under the naked eye or corrected vision. The specific appearance and color requirements can be determined by the supply and demand parties through standard samples.
nKaeerKAca-
GB/T39495—2020
Defects caused by the surface condition of the substrate or defects that still exist under normal operation shall not be rejected. The purchaser shall specify the acceptance limit of substrate defects.
3 Unit area mass
The unit area mass of the conversion film shall be measured in accordance with GB/T20017. 8.4
Adhesion
The conversion film shall adhere to the surface of the substrate and be free of powder. At present, there is no effective method to directly measure the adhesion of chromium-free conversion films on aluminum and aluminum alloys. When the conversion film is used as a coating base, the practical method is to measure the adhesion of another layer of organic film coated on the conversion film to evaluate the adhesion of the conversion film. If there is no special provision, the adhesion of the paint film on the conversion film shall be measured in accordance with GB/T9286. 8.5
5 Contact resistance
If there is a requirement for contact resistance, the contact resistance of the conversion film shall be measured according to QJ1827. For the convenience of using this standard, the measurement method of QJ1827 is shown in Appendix A. If required, the maximum resistance value and test frequency shall be agreed upon by the supplier and the buyer. 8.6
Corrosion resistance
Corrosion resistance shall be subjected to neutral salt spray test (NSS test) in accordance with GB/T10125. The samples shall be rated in accordance with GB/T6461. 9 Sampling and inspection
Unless otherwise specified, samples shall be randomly selected from the inspection batch according to the sample quantity specified in GB/T12609. Check the workpieces in the sample to confirm whether they meet the requirements of this standard. The inspection batch shall be judged to meet or not meet each requirement according to the sampling inspection procedure of GB/T12609.
Do not touch the surface of the sample within 24 hours after the conversion treatment, and any test shall be carried out after 24 hours. 4
rrKaerKAca-
A.1 Overview
Appendix A
(Informative Appendix)
Contact resistance measurement method
GB/T39495—2020
When the aluminum material after chromium-free conversion is used for the surface protection of spacecraft, electronic appliances and some instruments, its contact resistance is a very important characteristic parameter, so it is necessary to measure the contact resistance of the chromium-free chemical conversion film. In addition to the unit area mass of the film layer and the structure of the film, the factors affecting the contact resistance value are also related to the cleanliness, flatness, and pressure applied to the contact electrode of the film surface and the electrode surface. There are generally two methods for measuring contact resistance: the bridge method and the voltammetric method. The former has high measurement accuracy but the measurement process is cumbersome and is suitable for laboratory applications. The latter is convenient to measure and the measurement results can meet the requirements. A.2 Measurement method (QJ1827)
A.2.1 Principle
Based on Ohm's law R=U/I, that is, under constant current, a constant pressure load is applied between two electrodes of a certain area, and the voltage drop between the electrodes is measured with a microvoltmeter, and the contact resistance is calculated according to Ohm's law. See Figure A.1 for the schematic diagram. +12V
Stable mains
220 V
A.2.2 Measuring instrument
Stable voltage source
Stable intermediate source
Figure A.1
Instrument model: FCE-1 contact resistance tester; Instrument resolution: ±0.0012;
Electrode: Gold-plated electrode with a tip of 5cm2. A.2.3 Sample
The sample should be the same material as the workpiece and processed at the same time. +ay
Micro-manipulator
Upper plate
Lower outlet
Test piece
Schematic diagram of contact resistance measurement principle
rKaeerKAca-
Work
Zero
Press digital pressure meter
GB/T39495—2020
The surface of the sample should be flat, without burrs, scratches and other defects, and the surface roughness should be less than 0.8um. ??The size is 250mm×76mm×1mm aluminum plate, divided into 10 squares (see Figure A.2). 30
A.2.4 Measurement
A.2.4.1
×38=190
Figure A.2 Sample grid division
Turn on the power of the measuring instrument.
Turn the button to the zeroing position, adjust the zeroing knob, and make the digital display read zero. A.2.4.2
Turn the button to the working position,
A.2.4.3
Unit is millimeter
A.2.4.4 Wipe the electrode contact surface with a cotton ball soaked in anhydrous ethanol. Move the electrode to make the upper and lower electrodes contact, and then pressurize until the pressure gauge reads 165×10*Pa. The contact resistance value between the two levels should be zero. If it is not zero, it indicates that there is dirt on the end surface of the electrode. The electrode should be cleaned again and its resistance value should be measured again.
A.2.4.5 After unloading, place the cleaned test piece flat on the lower electrode, put down the upper electrode, pressurize until the pressure gauge reads 165×101Pa, and measure the resistance value of each square in turn. During the test, the edge of the test piece cannot touch any part of the instrument. Calculation of results
A.2.5
The contact resistance value of the test piece is the arithmetic mean of the contact resistance values ??of 10 squares, and the calculation formula is: Ri
Where:
R.,R,R.
Ri+R+R,++R
The contact resistance value of the test piece, in ohm (2); -The contact resistance value measured by 10 squares, in ohm (2). rKaeerKAca-1 Overview
Appendix A
(Informative Appendix)
Method for measuring contact resistance
GB/T39495—2020
When aluminum materials after chromium-free conversion are used for surface protection of spacecraft, electronic appliances and certain instruments, their contact resistance is a very important characteristic parameter, so it is necessary to measure the contact resistance of chromium-free chemical conversion film. In addition to the unit area mass of the film layer and the structure of the film, the factors affecting the contact resistance value are also related to the cleanliness, flatness, and pressure applied to the contact electrode of the film surface and the electrode surface. There are generally two methods for measuring contact resistance: the bridge method and the voltammetry method. The former has high measurement accuracy but the measurement process is cumbersome and is suitable for laboratory applications. The latter is convenient to measure and the measurement results can meet the requirements. A.2 Measurement method (QJ1827)
A.2.1 Principle
Based on Ohm's law R=U/I, that is, under constant current, a constant pressure load is applied between two electrodes of a certain area, and the voltage drop between the electrodes is measured with a microvoltmeter, and the contact resistance is calculated according to Ohm's law. See Figure A.1 for the schematic diagram. +12V
Stable mains
220 V
A.2.2 Measuring instrument
Stable voltage source
Stable intermediate source
Figure A.1
Instrument model: FCE-1 contact resistance tester; Instrument resolution: ±0.0012;
Electrode: Gold-plated electrode with a tip of 5cm2. A.2.3 Sample
The sample should be the same material as the workpiece and processed at the same time. +ay
Micro-manipulator
Upper plate
Lower outlet
Test piece
Contact resistance measurement principle diagram
rKaeerKAca-
Work
Zero
Press digital pressure meter
GB/T39495—2020
The surface of the sample should be flat, without burrs, scratches and other defects, and the surface roughness should be less than 0.8um. ??The size is 250mm×76mm×1mm aluminum plate, divided into 10 squares (see Figure A.2). 30
A.2.4 Measurement
A.2.4.1
×38=190
Figure A.2 Sample grid division
Turn on the power of the measuring instrument.
Turn the button to the zeroing position, adjust the zeroing knob, and make the digital display read zero. A.2.4.2
Turn the button to the working position,
A.2.4.3
Unit is millimeter
A.2.4.4 Wipe the electrode contact surface with a cotton ball soaked in anhydrous ethanol. Move the electrode to make the upper and lower electrodes contact, and then pressurize until the pressure gauge reads 165×10*Pa. The contact resistance between the two levels should be zero. If it is not zero, it indicates that there is dirt on the end surface of the electrode. The electrode should be cleaned again and its resistance value should be remeasured.
A.2.4.5 After unloading, place the cleaned test piece flat on the lower electrode, put down the upper electrode, pressurize until the pressure gauge reads 165×101Pa, and measure the resistance value of each square in turn. During the test, the edge of the test piece cannot contact any part of the instrument. Calculation of results
A.2.5
The contact resistance value of the test piece is the arithmetic mean of the contact resistance values ??of 10 squares, and the calculation formula is: Ri
Where:
R.,R,R.
Ri+R+R,++R
The contact resistance value of the test piece, in ohm (2); -The contact resistance value measured by 10 squares, in ohm (2). rKaeerKAca-1 Overview
Appendix A
(Informative Appendix)
Method for measuring contact resistance
GB/T39495—2020
When aluminum materials after chromium-free conversion are used for surface protection of spacecraft, electronic appliances and certain instruments, their contact resistance is a very important characteristic parameter, so it is necessary to measure the contact resistance of chromium-free chemical conversion film. In addition to the unit area mass of the film layer and the structure of the film, the factors affecting the contact resistance value are also related to the cleanliness, flatness, and pressure applied to the contact electrode of the film surface and the electrode surface. There are generally two methods for measuring contact resistance: the bridge method and the voltammetry method. The former has high measurement accuracy but the measurement process is cumbersome and is suitable for laboratory applications. The latter is convenient to measure and the measurement results can meet the requirements. A.2 Measurement method (QJ1827)
A.2.1 Principle
Based on Ohm's law R=U/I, that is, under constant current, a constant pressure load is applied between two electrodes of a certain area, and the voltage drop between the electrodes is measured with a microvoltmeter, and the contact resistance is calculated according to Ohm's law. See Figure A.1 for the schematic diagram. +12V
Stable mains
220 V
A.2.2 Measuring instrument
Stable voltage source
Stable intermediate source
Figure A.1
Instrument model: FCE-1 contact resistance tester; Instrument resolution: ±0.0012;
Electrode: Gold-plated electrode with a tip of 5cm2. A.2.3 Sample
The sample should be the same material as the workpiece and processed at the same time. +ay
Micro-manipulator
Upper plate
Lower outlet
Test piece
Schematic diagram of contact resistance measurement principle
rKaeerKAca-
Work
Zero
Press digital pressure meter
GB/T39495—2020
The surface of the sample should be flat, without burrs, scratches and other defects, and the surface roughness should be less than 0.8um. ??The size is 250mm×76mm×1mm aluminum plate, divided into 10 squares (see Figure A.2). 30
A.2.4 Measurement
A.2.4.1
×38=190
Figure A.2 Sample grid division
Turn on the power of the measuring instrument.
Turn the button to the zeroing position, adjust the zeroing knob, and make the digital display read zero. A.2.4.2
Turn the button to the working position,
A.2.4.3
Unit is millimeter
A.2.4.4 Wipe the electrode contact surface with a cotton ball soaked in anhydrous ethanol. Move the electrode to make the upper and lower electrodes contact, and then pressurize until the pressure gauge reads 165×10*Pa. The contact resistance value between the two levels should be zero. If it is not zero, it indicates that there is dirt on the end surface of the electrode. The electrode should be cleaned again and its resistance value should be measured again.
A.2.4.5 After unloading, place the cleaned test piece flat on the lower electrode, put down the upper electrode, pressurize until the pressure gauge reads 165×101Pa, and measure the resistance value of each square in turn. During the test, the edge of the test piece cannot touch any part of the instrument. Calculation of results
A.2.5
The contact resistance value of the test piece is the arithmetic mean of the contact resistance values ??of 10 squares, and the calculation formula is: Ri
Where:
R.,R,R.
Ri+R+R,++R
The contact resistance value of the test piece, in ohm (2); -The contact resistance value measured by 10 squares, in ohm (2). rKaeerKAca-
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