Study of hot-dip galvanised zinc and zinc-copper alloy coatings in chloride and chloride containing carboxylic acids media

Abstract

The purpose of the present paper is to have a comparative study on the response of hot dipped galvanised commercial zinc and zinc-copper alloy coating on mild steel towards chloride and chloride containing different carboxylic acids media. Response of Hot-dip galvanised Zinc & Zinc-Copper alloy coating on mild steel sheets were assessed in 3.5% NaCl solution and natural sea water obtained from Bay of Bengal. Weight loss was measured. Electrochemical test of the galvanised coatings was carried out in 2% & 3.5% NaCl solution and sea water. It was also carried out in 3.5% NaCl solution containing citric, formic and acetic acid respectively. OCP, Ecorr and icorr were obtained by using PARC 273 EG&G Potentiostat/Galvanostat. Minor alloying additions of copper in hot dip galvanised bath improves corrosion resistance of zinc coating on mild steel in chloride media. Aggressiveness of carboxylic acids in chloride medium on hot dip galvanised zinc-copper alloy and zinc coating can be arranged in the following order: Zinc-copper alloy-Formic acid < Citric acid < Acetic acid Zinc coating - Citric acid < Formic acid < Acetic acid