The salt spray test is an environmental test that uses the artificial simulated salt spray environmental conditions created by the salt spray test equipment to evaluate the corrosion resistance of products or metal materials.
Laboratory simulated salt spray tests can be divided into four categories:
Neutral salt spray test, acetate spray test, copper salt accelerated acetate spray test, alternating salt spray test.
(1) Neutral salt spray test (NSS test) is one of the earliest applications in the field of accelerated corrosion test. It uses a 5% aqueous solution of sodium chloride solution, and the pH of the solution is adjusted to a neutral range (6-7) as a solution for spraying. The test temperature is taken at 35 ° C, and the sedimentation rate of the salt spray is required to be between 1 and 2 ml / 80 cm 2 · h.
(2) The acetate spray test (ASS test) was developed on the basis of a neutral salt spray test. It is to add some glacial acetic acid to the 5% sodium chloride solution, the pH value of the solution is reduced to about 3, the solution becomes acidic, and the salt mist formed finally changes from neutral salt fog to acid. Its corrosion rate is about 3 times faster than the NSS test.
(3) Copper salt accelerated acetate spray test (CASS test) is a rapid salt spray corrosion test developed recently in foreign countries. The test temperature is 50 ° C, and a small amount of copper salt – copper chloride is added to the salt solution to strongly induce corrosion. . Its corrosion rate is about 8 times that of the NSS test.
(4) The alternating salt spray test is a comprehensive salt spray test, which is actually a neutral salt spray test plus a constant damp heat test. It is mainly used in cavity-type machine products. Through the penetration of the tidal environment, salt spray corrosion is generated not only on the surface of the product but also inside the product. It is to alternate the product under the salt water and hot and humid environment conditions, and finally check whether the electrical and mechanical properties of the whole product are changed.
Salt spray test method:
Generally, the corrosion resistance of the product with the lighter degree of corrosion is determined by visual inspection or low-power optical microscopy before and after the test. During the test, the temperature, salt spray concentration, humidity/salt mist cycle, and length of test time are used as the severity level.
