Salt spray testing is widely used in many manufacturing industries. For example, in automobile industry, power battery, automobile assembly and parts must resist salt spray corrosion. Therefore, factories producing those products must do the salt spray test to make sure that the product reach the qualification.   The salt spray test is normally done by a test machine. There are many kinds of machines can do the salt spray test. One of them is called alternating salt spray laboratory. It can simulate marine climate and assess the salt spray corrosion resistance of specimen and their protective layer. The alternating salt spray laboratory is complied with ISO12405-3:2014.   There will be three stages of the testing process: A. It will spray salt spray at 15℃ to + 35℃ for 2 hours. B. Then when the temperature reaches (40 ± 2) ℃ and relative humidity reaches (93 ± 3)%, placed the specimen for 20 to 22 h. C. After that, when the temperature reaches (23 ± 2) ℃ and the relative humidity is 45% to 55%, placed the specimen for 3 days. Stage A and stage B are one cycle, repeating 4 cycles and then proceed stage C to form a test cycle and completing 4 test cycles at the test.