Effects of inorganic additions on the performance of manganese-based conversion treatments I. Danilidis a , J. Hunter b , G.M. Scamans c , J.M. Sykes a, * a Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK b Novelis Global Technology Centre, 945 Princess Street, Kingston, Ont., Canada K7L 5L9 c Innoval Technology Ltd., Banbury, Oxon OX16 1TQ, UK Received 10 July 2006; accepted 3 August 2006 Available online 28 September 2006 Abstract The electrochemical behaviour of permanganate-based no-rinse conversion coatings on AA3003- H14 aluminium alloy shows that they have promise as an alternative to toxic chromate-based coat- ings. A selection of inorganic additions has been made here to a simple 0.1 M KMnO 4 formulation investigated previously. The performance of the different coatings has been evaluated from poten- tial–time and polarisation measurements in 0.5 wt % (0.085 M) NaCl solution for periods up to 3 days. The addition of fluoride ions produced no benefit, whereas Al(NO 3 ) 3 shows an improvement when added in small amounts. Tests with the individual ions reveal that it is Al 3+ cations, rather than NO À 3 anions, which produce the greatest benefit. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: A. Aluminium; A. Permanganate; B. Polarisation; C. Pitting corrosion; C. Oxide coating 1. Introduction The environmental hazards of conventional chromium-based, conversion coatings [1–4] have led to a worldwide search for an alternative. Manganese has been chosen here due to its chemical similarities to chromium (structural and electronic) [5]. It has previously been shown that permanganate-based conversion pre-treatments can perform well [6]. 0010-938X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2006.08.007 * Corresponding author. Tel.: +44 1865 273726; fax: +44 1865 273789. E-mail address: john.sykes@materials.ox.ac.uk (J.M. Sykes). Corrosion Science 49 (2007) 1559–1569 www.elsevier.com/locate/corsci