Testing

Metal corrosion is a spontaneous oxidation process. In the salt spray environment, because the salt spray liquid exists as an electrolyte, it increases the chance of forming a micro battery inside the metal, accelerates the electrochemical corrosion process, causes the metal or coating to corrode, rust, and blisters. Thereby it appears situations like corrosion destruction of components and fasteners , blockage or adhesion of the moving parts of mechanical parts and components, jam or fail of the moving parts, open or short circuit of fine wire and printed circuit board, and breakage of component legs, etc. At the same time, the conductivity of the salt solution greatly reduces the surface resistance and volume resistance of the insulator, and the resistance between the salt spray corrosion product and the dry crystal (salt grains) of the salt solution will be higher than that of the original metal, which will increase the resistance and voltage drop of the part, affect the electric shock action, and seriously affect the electrical properties of products. Therefore, the salt spray test for electrical and electronic products is an important method to investigate the corrosion resistance of products.

The salt spray test has three types: neutral salt spray test (N SS), acetic acid salt spray test (AA SS) and copper accelerated acetic acid salt spray test (CA SS) which also known as copper chloride acetic acid salt spray test. Among them, the most widely used is the neutral salt spray test. The neutral salt spray test is mainly used to inspect metal materials and metal coatings or non-metallic inorganic coatings on metals, as well as to inspect coating systems. In contrast, acetic acid salt spray and copper accelerated acetic acid salt spray are generally only used for the inspection of metal coatings and not for the inspection of organic coatings.

The purpose of the salt spray test is to assess the salt spray corrosion resistance of the product or metal material, and the determination of the salt spray test result is the main evaluation factor for the product quality. Whether the judgment result is correct and reasonable is the key to correctly measure the salt spray corrosion resistance performance of a product or coating. The results of the test include blistering, rust, reduction in adhesion, and the spread of corrosion from scratches, etc. As the relevant standards for the evaluation of salt spray test results are not universal, the determination method is also under discussion. In various standard systems, the evaluation of salt spray result is recommended to use: "GB/T 1766-2008 Rating Method for Paint and Varnish Coating Aging" and "GB/T 6461-2002 Rating of Specimens After Corrosion Test of Metal and Other Inorganic Coatings on Metal Substrates".

Common salt spray corrosion types:

1. General surface corrosion

The material is uniformly removed from the entire material-erosion medium contact surface. This is a very common type of corrosion. The common types are flaky corrosion and surface corrosion.

2. Pitting corrosion (hole corrosion)

The corrosive medium corrodes a limited area. It penetrates into the material to form holes or pits, the depth of which is almost always greater than its diameter. In fact, no metal is removed on the surface outside the pitting area. Pitting corrosion is often caused by halide ions.

3. Crevice corrosion

Corrosion occurs mainly in narrow gaps, which is caused by the concentration difference in the corrosive medium, such as the result of long oxygen diffusion channels. This type of corrosion creates a potential difference between the two ends of the gap, leading to increased corrosion in poorly ventilated areas.

4. Dezincification

Zinc is selectively dissolved from brass, leaving behind a porous red copper structure. The process of denickeling and dealuminization is similar to that.

5. Rust

Formation of ferrous oxide and hydroxide corrosion products on iron and steel.

6. Loss of light

The gloss of the surface of the object is reduced.