Fundamental aspects of corrosion and delamination behaviour of novel zinc alloy coatings and Zn-intermetallic phasesFunded under: ECSC-COAL-STEEL-RTD C
This project addressed one of the most innovative topics in current steel research. Improved corrosion protection and perhaps thus enabling the use of much thinner coating thickness and particularly the potential compatibility for direct painting - i.e. painting without prior conversion treatment - makes zinc alloy coatings very attractive. Two main approaches for sample preparation were followed: PVD application of the alloying element and subsequent diffusion alloying and hot-dipped galvanised (HDG)-based coating preparation from an alloy melt. The detailed characterisation of the prepared samples, in combination with fundamental mechanistic studies, electrochemical investigations, and corrosion and delamination studies, provided very important information for the design of improved zinc alloys. For the HDG-based zinc alloy coatings, however, their structure turned out to be too complex to give definite instructions at this stage. The microstructure of the hot-dip galvanised Zn-Al-Mg based samples is of critical importance: with same composition, completely different behaviour was observed. It certainly can be said that the galfan-based high Mg content coatings perform best and this seems also to be correlated to the very thin eutectic structure Zn/Al/Mg, which also showed promising effects during delamination of directly painted samples. For the diffusion coupled coatings, a significantly improved performance requires the combination of the good delamination-inhibiting properties of Mg (Zn-Mg compatible with direct painting) with the good corrosion performance of alloying components such as Al or Ti. For the case Zn-Mg-Ti this was demonstrated. However, Ti at the surface is not compatible with direct painting.
Bibliographic Reference: EUR 23178 EN (2009), 141 pp. Euro: 20
Availability: Katalogue Number: KI-NA-23178-EN-S The paper version can be ordered online at: http://bookshop.europa.eu
ISBN: ISBN: 978-92-79-07649-7
Record Number: 201010008 / Last updated on: 2010-01-07
Original language: en
Available languages: en