Where the
world gathers for metal finishing
Q&As since 1989


-----

White spots on zinc plating

2004

It would be grateful if you could provide me some information on the following problem faced by us.

Problem: white spots are seen on Zinc Plated and Blue passivated (Clear Zinc) Cold rolled steel sheets. These spots are found to be of non corrosive when subjected to Salt spray test for 12 hours using 5% salt solution under 35 °C. The white spots are not normally seen when viewed straight but can be seen when looking at angles.

The Questions are

1) Is this white spots in any way lead to corrosion?
2) How this white appear/
3) Is there a way to avoid this white spots
4) Is there any chemical to remove this white spots when appeared?

Would appreciate if you could answer to the above questions.

Thanking you in advance.

MOOSA CK
'electronics mfgr - Trivandrum, Kerala, India

No response to my query was received. This is a follow-up letter.

MOOSA CK [returning]
Electronics Manfctr - Trivandrum, Kerala, India
2004

Are you talking about acid zinc barrel plating? If yes, than this problem is what we call "Barrel Marked ".

Chua
- Selangor, Malaysia
2004

Ed. note: full name please, Chua.

---

2004

Dear sir,

The white spot on your component is the white rust which normally occurs in zinc plating with blue chromate between 24 to 48 hour. If you wanted to eliminate this problem use better trivalent chromate with top coat sealant which will give you around 100 hours salt spray test to white rust. The processes are available in south India.

P. Gurumoorthi
electroplating process chemicals - Chennai, Tamilnadu, India