[求助] How to test for good passivation/phosphating?

I wondering whether there is any test for testing the passivation on the surface of the metal. Normally Salt Spray Test has been carried out for testing coating on the surface of the metal, however when I asked my supplier who carry out passivation for our product, they replied that salt spray test is not the correct test to perform for passivated surface. So may I request you whether can you recommend any test for passivated metal surafce

Is this zinc phosphate applied over a ferrous substrate? What is the purpose of the phosphate, corrosion protection or as a pretreatment for something else (paint, adhesive, etc.)? What did your supplier recommend?

Phosphate coatings are often tested using neutral salt spray tests, with the number of hours depending on thickness/coating weight, use of oil or topcoat, etc. Usually in the range of 2 to 96 hours.

Do you want to test for stainless steel or carbon steel? Please tell me details.

Hello
You can have a try:Blue point method /Copper surface contact test method/The anodic polarization curve

采用硫酸铜测试是一个比较好的选择！