Corrosion Behaviour of Zinc and Zinc Alloy Coated Steel in Preservative Treated Timber

SUMMARYThe corrosion behaviour of a wide range of zinc and zinc alloy coated steels, in wood preservative solutions and timber environments, has been investigated using electrochemical measurements. For rapid evaluation of corrosion performance, the corrosion tests were carried out on specimens immersed in copper/chromium (simulated CCA) ‘salt’ and ‘oxide’ formulated solutions. To more closely simulate service conditions, an experimental cell was developed in which coated steels were in contact with CCA treated timber. The corrosion behaviour was evaluated by determining corrosion potential and corrosion current, and examination using scanning electron microscopy. The experimental cells demonstrated that the humidity of the environment was important, significant corrosion of coatings occurring when the moisture content exceeded 18–20%.‘Salt’ formulated solution and ‘salt’ impregnated timber resulted in more corrosive environments than their ‘oxide’ formulated equivalents. The Zn-55% Al (hot-dip galvanized) and Zn-12.5% Ni (electrodeposited) coated steels were found to give significantly better corrosion performance than pure zinc or the other alloy coatings investigated.