Test method and standard for coating thickness

The thickness of the coating is an important index to measure the quality of the coating, which directly affects the corrosion resistance and electrical conductivity of the workpiece, and then has a significant impact on the reliability and service life of the product. Therefore, the method of accurately measuring the thickness of the coating is very important. Various methods of measuring coating thickness are introduced in this paper.

1. Destruction method

Failure methods are a set of methods characterized by the destruction or damage of the coating under test during testing. These methods include:

Dissolution method: This method determines the average thickness of the entire coating by soaking the sample in an appropriate solution to dissolve the coating or base metal, and then comparing the weight of the sample before and after dissolution or using chemical analysis to determine the quality of the coating.

Coulomb method: The Coulomb method uses a constant direct current flow through the electrolytic solution to dissolve the metal anode of the coating, and calculates the thickness of the coating according to the amount of electricity consumed. This applies to local thicknesses of single or multi-layer single metal coatings.

Timing liquid flow method: The local coating of the sample is dissolved under the action of liquid flow, and then the time required for dissolution is recorded to calculate the coating thickness.

Test method for coating thickness

2. Non-destructive method

Lossless methods are a group of methods that are characterized by not destroying the coating under test during testing. These methods include:

Magnetic method: Suitable for measuring the thickness of non-magnetic coating on magnetic metal substrates. The measurement error of this method is usually small, but may be slightly less accurate for thinner coatings.

Eddy current method: The high-frequency magnetic field generated by the high-frequency coil is used to generate eddy current in the sample to be tested, and the thickness of the coating is determined according to the amplitude and phase of the eddy current. This method is suitable for thickness measurement of non-conductive coating on non-magnetic metal substrate.

β-ray reflection method: The thickness of the coating is determined according to the intensity of the β-ray reflected by the coating. Suitable for thin precious metal coating.

X-ray fluorescence method: By measuring the secondary X-rays generated on the metal surface, the thickness of the metal coating on the metal or non-metal substrate can be measured, and the composition of the alloy coating can also be determined.

Test method for coating thickness

3. Other methods

In addition to the above destructive and non-destructive methods, there are some other methods used to measure the thickness of the coating, such as metallographic microscopy, profilometer, interference microscopy, double beam microscopy and so on. These methods have their own advantages and applicability in specific situations, and the appropriate method can be selected for testing according to the needs.

Summary and suggestion

The accurate measurement of the thickness of the coating is essential to ensure the quality of the product. The choice of the appropriate test method depends on the type of coating being tested, the thickness range and the test accuracy requirements. In addition, international and industry standards provide detailed test procedures and requirements to ensure the accuracy and repeatability of tests. Therefore, when testing the thickness of the coating, it is recommended to refer to the relevant standards and select the appropriate test method to ensure the quality and performance of the product.