Accession Number : AD0778277

Title :   The Initiation of Corrosion of Chromated Zinc Electroplate on Steel,

Corporate Author : DEFENCE STANDARDS LABS MARIBYRNONG (AUSTRALIA)

Personal Author(s) : Williams,L. F. G.

Report Date : 13 MAR 1973

Pagination or Media Count : 8

Abstract : The first visible sign of corrosion of chromated zinc electroplate is usually the appearance of small dark spots on the surface. These areas, which are produced during exposure to the ASTM B117 Salt Spray Test, have been examined by electron probe micro-analysis (EPMA) and scanning electron microscopy (SEM). The initial step seems to be the breakdown of the chromate film followed by corrosion of the zinc plate. Surprisingly, the chromate layer remains over the corrosion product (basic zinc chloride) and the apparent dark colour originates from the change in optical properties of the film and the underlying zinc. Copper-encriched deposits have also been examined. Minor corrosion of the steel under the zinc was evidenced by analysis of the corrosion product by EPMA and by examination of the steel surface by SEM. (Author)

Descriptors :   *Corrosion, *Zinc, *Steel, *Chromates, Salts, Coatings, Electron microscopy, Electron probes, Discoloration, Australia

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE