The authoritative public forum
  for Metal Finishing since 1989
-----

Acid Zinc Cobalt v/s Alkaline Zinc Plating

2007

Kindly suggest whether Acid Zinc Cobalt will give better corrosion protection than Alkaline Zinc Plating on sheet metal components with trivalent passivations.

Also which is a easy bath to maintain.

Thanks for the reply.

HEMAL NAGDA
PLATING SHOP - MUMBAI, MAHARASHTRA, INDIA

---

Dear Mr Nagda,

In India there are limited choices in Trivalents. The acid zinc cobalts impart a welcome hardness in the deposit leading to better corrosion protection where red rust is concerned, but shows little or no improvement of the white rust performance. However Cobalt as an alloy is not generally welcome.

The current trivalent passivation products available in India work better on alkaline zinc plated surfaces, but do not substantially improve the red rust performance.

I personally would choose the chemistry after considering the better process where plate-abilty of the article is concerned in the first place.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2007

---

2007

Hi Hemal,
Your one line question prompt us to give many line answers!
1. As Mr. Vahanwala said, you have to choose the chemistry which is suited to your customer requirement.
2.Though plating is mainly responsible for Red Rust capability, I found about 10-15% increase in RR by using Alkaline Cyanide Free baths.
3.I have seen Alkaline Zinc iron with trivalent black passivation with top coat giving over 1200hrs Red rust.
4.If you are looking for Red rust of 400 hrs+,u may opt for Acid Chloride Cobalt Zinc bath with trivalent passivations.
5.There are Trivalent passivations available with out top coats which will give enhanced WR and that means automatically will give you enhanced Red Rust.
6.And finally it comes back to Vahanwala's suggestion of choosing the chemistry as per your customer need.but some how cannot agree with Mr. Vahanwala that in India there is only limited choice in Trivalent passivations.The whole world is now looking at India and apart from all the small and big supply houses having wide range of trivalent passivations,there are more than equal nos. of overseas suppliers actively associated with many of them.
regards.

T.K. Mohan
plating process supplier - Mumbai, India