White Spots When Salt Spray Testing Zinc With Yellow Passivation Parts

Hello, I am Bahadur Singh working in electronic company. We are using many components made out of deep drawn steel. My question is about plating on this component.

1) If parts are Tin plated(3-4 microns) over nickel (2-3 microns), are tin plated parts tested for salt spray test? If Yes than which salt is used to test?

2) Why do white spots appear on zinc plated (with yellow passivation) parts?

3) What is a suitable method to do zinc plating with yellow passivation on hollow pipe (Material-Mild steel) of I.D 1 inch and length 100 mm.

Salt spray testing is done when the specification requires it or when you want quality data.

When you ask what salt, it would indicate that you have not yet read ASTM B117 or an equivalent test method. It is by definition a very strict process using sodium chloride of a specified purity.

The white spot is the corrosion or "rust" of zinc. It might indicate a poor passivation, but you have not given conditions of how it occurred. Since this is probably a high volume item, the normal method would be barrel plating using either a cyanide or an alkaline zinc process.

Dear Mr Singh. Closer to home you may want to refer to IS 1573 and IS 9844 which are Indian Standards for Zinc plating and SST. regards,