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This post was last edited by Wang Wei2 on 2025-10-19 at 10:54. The atmospheric exposure corrosion test involves conducting actual corrosion tests on coated samples on sample stands, either outdoors or indoors, under natural atmospheric conditions. The protective lifespan of these coatings is determined by regularly observing and measuring the characteristics of their corrosion process as well as the rate of corrosion. Atmospheric exposure testing is an important method for accurately assessing the corrosion resistance of coatings, and its results are typically used as a basis for establishing standards for coating thickness. The specific test methods can be referred to the **standard GB 6464-1986 \"General rules for corrosion testing by static outdoor exposure of metals and other inorganic coatings\". The selection of corrosion test conditions for atmospheric exposure should be the same as or similar to the actual conditions in which the workpiece is used. Generally, based on the environmental conditions of the area where the exposure site is located, atmospheric conditions are divided into four categories (including indoor and outdoor): industrial atmosphere, marine atmosphere, rural atmosphere, and suburban atmosphere. The exposure site should be located in a completely open area, where it is fully exposed to the elements of the atmosphere (air, sunlight, rain, dew, fog, frost, snow, etc.). There should be a certain distance between the surrounding buildings, trees, and sample holders, to ensure that the shadows cast by these buildings and trees do not fall on the samples being tested at any time. There are three methods for exposing samples to the atmosphere: 1) Outdoor exposure, which involves placing the samples directly on a frame outside. The frame is made of materials resistant to corrosion, with the specimen facing south on it. The height of plants near the framework should not exceed 0.2m ； 2) Semi-enclosed exposure: The sample is exposed under a covered structure to prevent direct exposure to solar radiation and atmospheric precipitation, or it is exposed in a partially enclosed space such as a Stevenson box ； 3) “Fully enclosed” exposure to sunlight, during which external factors have a very limited impact on the sample. The specimens used for atmospheric exposure testing must have an area of at least 50 cm2 (5 cm × 10 cm). The specially prepared specimens should be flat in shape, with the length of one side preferably being an integer multiple of 50 mm, and a thickness of 1–3 mm. The number of specimens of the same type must be no less than three. The sample should be thoroughly cleaned before exposure to direct sunlight in order to remove contaminants from the surface of the coating. Each specimen should have a permanent identifier, such as a stamp or a plastic tag with engraved markings. Before the test begins, the sample should be recorded using a dedicated test record sheet, detailing information such as the sample number, coating structure, thickness, and surface finish. A test outline should also be prepared (including the purpose of the test, test requirements, inspection intervals, etc.). For each sample, 1 to 3 pieces should be kept in a desiccator for comparison and observation during testing. It is best to introduce the test samples before the wet and rainy seasons each year; it is recommended to do this in April–May or September–October of each year. Since the rate of atmospheric corrosion is very slow, the test duration should preferably be 1 to 20 years. After the sample begins to be exposed, inspections should be carried out frequently during the first 3 months, generally 2 to 3 times per month. When conducting inspections, attention should be paid to the time when corrosion spots first appear, and detailed records should be kept. Check once a month after 3 months, and once every 3 months after 1 year. For samples exposed outdoors in winter, in areas where snow falls (that is, during winter), the snow accumulated on their surface should be wiped off regularly. When taking samples, do not let your hands make direct contact with the main surface. It is not allowed for the two specimens to come into contact or rub against each other, in order to prevent artificial mechanical damage or electrochemical corrosion that could lead to errors in the test results. The evaluation of test results can be based not only on the salt spray testing method but also on the corrosion rate on the surface of the specimen to determine the corrosion grade.