How to test for good passivation/phosphating?

[ndsram]

HI,

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

BR
N D Senthil Ram

 

[TVP]

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.

 

[swall]

ndsram--see my answer re copper sulfate test in the Corrosion Forum.

 

[ndsram]

Dear swall
I thank you for your reply
Dear TVP
My product would be NdFeB magnet. It is a pretreatment and just phosphating on the magnet surface.its mainly for good adhesion and its our requirement. Please let me know whether if there is any standard for testing passivation. For our passivation supplier does not recommend salt spray test and if tested in salt spray, the corrosion are with in minutes

 

[IRstuff]

Depends on what the objective requirement of the coating is. Generally, a coating is required to be pinhole free, so a test that reveals the locations of pinholes might be sufficient.

TTFN
faq731-376

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[ndsram]

THank you IRStuff

I finally has to comply with A967 standard for passivation testing on metal surface

 

[TomDOT]

Okay, if ASTM A967 is your spec, then go to ASTM A967 to determine which tests to use. It has 6 different tests listed, including a 2h salt spray to ASTM B117, which should show no corrosion. If there is corrosion "within minutes" - perhaps you passivation supplier is not fully passivating the parts.

Of course, A967 is for passivation of STAINLESS STEEL parts, not NdFeB parts. YMMV.

 

[ndsram]

Yes I agree that the A967 is for testing passivation on Stainless Steel, However, with No standard for testing passivation on NdFeB magnet is available, I thought I can use this standard, provided that a few test like, Salt Spray Test, Salth Water Immersion test & Humidity Test may be carried out and result may be standardized with the magnet supplier. By this method we can atleast know some standardized value to arrive for good passivation

Hope you do agree with me

Regs
N D Senthil Ram