Effect of HCl pre-treatment on corrosion resistance of cerium-based conversion coatings on magnesium and magnesium alloys Katya Brunelli, Manuele Dabala ` * , Irene Calliari, Maurizio Magrini Department of Mechanical Innovation and Management, University of Padua, Via Marzolo 9, 35131 Padua, Italy Received 10 October 2003; accepted 21 June 2004 Available online 18 September 2004 Abstract The corrosion protection afforded by a cerium conversion coating, formed by immersion in a solution containing rare earth salt and hydrogen peroxide, on pure magnesium and two mag- nesium alloys, AZ91 and AM50, has been studied. The effect of HCl pre-treatments on the morphology and on the corrosion resistance of the cerium conversion layer was investigated. A thicker and more homogeneous distribution of the conversion coating was obtained when the sample surface was pre-treated with acid. Higher amounts of cerium on the surface of the pre-treated samples were detected. The cerium conversion coating increased the corrosion resistance of the alloys because it ennobled the corrosion potential and decreased both the anodic and cathodic current. The acid pre-treatment further increased the corrosion resistance of the coated alloys. After five days of immersion in chloride environment the untreated sam- ples showed localized corrosion while the chemical conversion coated samples appeared unaffected. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Magnesium alloys; Conversion coating; Cerium; Corrosion 0010-938X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2004.06.016 * Corresponding author. Tel.: +39 49 827 5499; fax: +39 49 827 5500. E-mail address: manuele.dabala@unipd.it (M. Dabala `). Corrosion Science 47 (2005) 989–1000 www.elsevier.com/locate/corsci