what’s salt spray test?
corrosion is the destruction or deterioration of a material or its properties under the action of the environment. most corrosion occurs in the atmospheric environment, which contains corrosive components and factors such as oxygen, humidity, temperature changes and pollutants. salt spray corrosion is a common and most destructive atmospheric corrosion. the corrosion of salt spray on the surface of metal materials is caused by the electrochemical reaction of the chloride ions contained in the metal surface through the oxide layer and protective layer of the metal surface and the internal metal. at the same time, chloride ions contain a certain amount of hydration energy, and are easily absorbed by pores and cracks on the metal surface to displace and replace oxygen in the chlorinated layer, turning insoluble oxides into soluble chlorides, and turning the passivated surface into an active surface, resulting in a very bad adverse reaction to the product. 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.
application scenarios of salt spray test
the purpose of the salt spray test is to evaluate the salt spray corrosion resistance quality of products or metal materials. the test object may have permanent or temporary corrosion resistance, or may not have permanent or temporary corrosion resistance.
salt spray test can be used as a method to check whether the tested material has anti-corrosion performance, can be used as a test method to quickly evaluate the discontinuity, porosity and breakage of organic and inorganic coatings, and can also be used as comparison of the workmanship quality of the samples with similar coatings.
salt spray test type | applicable product range |
neutral salt spray test (nss) | metals and their alloys, metal coatings (anodic or cathodic), conversion coatings, anodic oxide coatings, organic coatings on metal substrates |
acetic acid salt spray test (aass) | copper nickel chromium or nickel chromium decorative coatings, also suitable for anodized coatings of aluminu |
copper accelerated acetic acid salt spray test (cass) | copper nickel chromium or nickel chromium decorative coatings, also suitable for anodized coatings of aluminum |
evaluation of test results
there are various methods for judging and expressing the results of the salt spray test, for example, expressing according to the characteristics of corrosion, rating according to the percentage of the corrosion area, expressing according to the corrosion rate, expressing according to the weight loss and so on.
according to gb/t 6461 "methods for corrosion testing of metallic and other inorganic coatings on metallic substrates-rating of test specimens and manufactured articles subjected to corrosion tests", the results of rating according to corrosion area are as follows:
protection rating | appearance rating classification of overlay damage types | performance rating examples of evaluation results | |
defect area a (%) | rating rp | ||
flawless | 10 | a spotting and/or color change due to damage to the overlay (different from the color of apparent base metal corrosion products) b is hard to see, even invisible darkening caused by corrosion of the cover layer c corrosion products of anode cover d corrosion products of cathode coating e surface pitting (corrosion pits may not extend to the base metal) f chipping, peeling, peeling g bubbling h cracking i crack j chicken claw or stellate defect | a: the specimen exhibits base metal corrosion over 0.1% of the total area and the remaining surface of the specimen exhibits moderate spotting over 20% of the area: 9/2ma b: there is no base metal corrosion on the sample, but mild corrosion of the anodic coating of less than 1.0% of the total area: 10/6sc c: 0.3% of the area of the sample shows base metal corrosion, and the corrosion products of the anodic coating cover 0.15% of the total area. and the uppermost electrodeposited layer has a slight bubbling area exceeding 0.75% of the total area: 7/8vsc, 6mc |
0 | 9 | ||
0.1 | 8 | ||
0.25 | 7 | ||
0.5 | 6 | ||
1.0 | 5 | ||
2.5 | 4 | ||
5.0 | 3 | ||
10 | 2 | ||
25 | 1 | ||
50 | 0 | ||
testing requirements and quotations
test standards | judgement standards | sample size | test period |
gb/t 10125 | gb/t 6461 | complete samples of 4 pieces and above | the test period should be selected according to the relevant standards of the tested material or product. if there is no standard, it is admirable for the relevant parties to negotiate and decide. the recommended test cycle is 2h, 6h, 24h, 48h, 72h, 96h, 144h, 168h, 240h, 480h, 720h, 1000h |
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