Steps and characteristics of cyclic salt spray corrosion test

Date：2021-10-19 13:37:00Views：1263

Cyclic corrosion test (CCT) has been developed in the automotive industry in recent years. It is a method to accelerate the corrosion failure in the real world under the condition of laboratory control. As the name suggests, the test includes different climates, which will cycle automatically, so the tested samples will experience the same changing environment as nature. The purpose is to cause naturally occurring fault types, but faster, i.e. acceleration. By doing so, manufacturers and suppliers can more accurately predict the expected service life of their products. The lack of correlation between the results obtained by the traditional salt spray test and the "real-world" atmospheric corrosion of vehicles makes the automotive industry lack a reliable test method to predict the expected service life of its products.

The test phase is based on the results mainly from the "real world" exposure site. Initially, the automobile company led by the Japanese automobile industry developed its own cyclic corrosion test. For different automobile manufacturers, these tests develop in different ways, and such tests are still industry-specific to a large extent, and there is no real international CCT standard. However, they usually need to create most of the following conditions in a repeating order or "loop", although it is not necessary to follow the following order.

Salt fog "pollution" stage

Although in some cases direct impact by this can be similar to the traditional salt spray test, complete immersion of salt solution in the test sample or even in salt water is necessary. However, the duration of this "pollution" phase is usually shorter than the traditional salt spray test.

Air drying stage

Depending on the test, this can be carried out at ambient temperature or elevated temperature, and the relative humidity can be controlled or not. It can often be achieved by continuously introducing relatively fresh air around the test sample at the same time. It is generally required that the tested sample should be significantly "dry" at the end of this test phase. Condensation humidity "wet" phase, which is usually carried out at high temperature and high humidity of 95% - 100% RH. The purpose of this stage is to promote the formation of condensation on the surface of the tested sample.

Controlled humidity / humidity cycle phase

This requires that the test sample be exposed to an environment of controlled temperature and controlled humidity, which can be constant or circulated between different levels. You can also specify the rate of change when cycling between different levels.

The above only represents the more common requirements and is not exhaustive. What are the characteristics of cyclic salt spray corrosion test? The acceleration of accelerated cyclic salt spray corrosion test is mainly reflected in three aspects:

1）Salt spray is continuously sprayed to ensure continuous surface corrosion.In the process of cyclic salt spray corrosion, a quantitative salt spray will be sprayed out, and a series of changes will occur to the tested piece, including rust, bubbles, etc. the salt spray is continuously supplied in this process, which can continuously corrode the tested piece.

2）Salt fog accumulation will diffuse to the inside of the tested part in the hot and humid stage.After the tested piece enters the damp heat stage, although no salt mist is sprayed on the surface, the originally accumulated salt mist will still adhere to the surface of the tested piece, penetrate internally in the damp heat environment and deeply corrode the tested piece.

3）The drying stage accelerates the surface corrosion rate.After the tested piece enters the drying stage, the relative humidity will gradually decrease, which will increase the concentration of salt solution, make it more corrosive and accelerate the corrosion of the tested piece. In the process of cyclic corrosion salt spray test, the tested piece is always in the state of cyclic alternation. The traditional salt spray test method is too simple. There is only serious corrosion on the surface of the tested piece. Although it will penetrate into the interior, the corrosion simulation will deviate from the actual situation. Cyclic alternation corrosion will alternate the three states of drying, damp heat and salt spray, and the simulated environment is closer to the reality, Accelerate the test speed and make the test results more accurate and true.

The environment simulated by the complex cyclic salt spray experiment is closer to the atmospheric environment, and there are many cyclic components. It can be reasonably selected in combination with the actual test requirements, close to the use environment as much as possible, and the complexity of the test is higher. Due to the need to switch multiple cycle combinations for cyclic salt spray corrosion, special operators need to be arranged. In recent years, with the continuous improvement of scientific and technological level, a single test chamber can be used to complete all test tasks. However, at present, domestic test chambers can not support all tests, and some imported products can be completed.

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