Progress in Organic Coatings 46 (2003) 84–90 Influence of prephosphating on painted electrogalvanized steel G. Bustamante a , F.J. Fabri-Miranda a , I.C.P. Margarit b,c,∗ , O.R. Mattos b a USIMINAS, Ipatinga, MG, Brazil b “Professor Manoel de Castro” Corrosion Laboratory, PEMM/COPPE/UFRJ, PO Box 68505, CEP 21945-970, Rio de Janeiro, RJ, Brazil c Inorg. Proc. Dep., EQ/UFRJ, Rio de Janeiro, RJ, Brazil Abstract The role of phosphate layers as lubricant and painting adhesion promoters is well known. Nowadays, in the automotive industry phosphating treatments are used twice, before and after the forming process of car panels. The effects of a double phosphating on the anticorrosive performance of the whole material are not well established. The present study evaluates the corrosion behavior of electrogalvanized steel with and without a phosphating treatment before mechanical deformation (prephosphating) which simulates the forming process in automotive industries. The samples are formed in a hydraulic press, rephosphated and painted. The composition, weight and morphology of the zinc and phosphate layers are characterized by X-ray diffraction, plasma spectrometry, weight-loss measurements and scanning electron microscopy (SEM). The analysis is complemented with electrochemical impedance taken before and after the forming processes. Results suggest a beneficial role for prephosphating, which is confirmed by cyclic corrosion tests of painted samples. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Phosphating; Electrogalvanized steel; Coatings; Impedance 1. Introduction Zinc and zinc-alloys coated steels are very used in the automotive industries. However, these coatings are sensitive to abrasion and during the forming process cold-weld oc- curs with the tools. Therefore, not only the tools are injured, but also the anticorrosive resistance of the whole material is lessened [1]. In order to avoid such problems, steel-makers have introduced a phosphating pretreatment (prephosphat- ing) of the sheets [1–5]. Indeed, the so-formed phosphate layer better absorbs the lubricant oil, improving the material formability [2]. Once the forming is finished, the car body is rephosphated (postphosphated) and painted. Steps on the phosphating treatment, such as: surface cleaning, activation, phosphating itself and finish washing, involve partial dissolution of the zinc coating [6]. Although nowadays widely employed, the effects of a double phos- phating (pre + post) on the adhesion properties of the phosphate layer and on the anticorrosive performance of the whole material are not well known. The main purpose of this paper is to study the influence of prephosphating on the performance of electrogalvanized ∗ Corresponding author. E-mail addresses: margarit@metalmat.ufrj.br (I.C.P. Margarit), omattos@metalmat.ufrj.br (O.R. Mattos). steel. Prephosphated samples are submitted to forming pro- cesses and to subsequent steps of phosphating (postphos- phating) and painting. Samples are withdrawn from each step for characterization and the results are compared with samples without prephosphating. Plan samples (without me- chanical work) are also studied to verify the influence of the forming processes. The adhesion properties of the final phosphate layer are investigated on painted samples submit- ted to cyclic corrosion test. 2. Experimental A steel coil with extra-deep formability properties (inter- stitial free), commonly employed in the automotive indus- try, is electrogalvanized in an industrial process (Gravitel ® ). After electrogalvanization, the coil is divided into two parts. One part is withdrawn from the continuous process and the other part follows into a phosphating spray line (prephos- phating). The solutions are Fixodine ZL ® for the activation and Granodine 5854 ® for the phosphating itself. Panels of 40 cm × 40 cm, with and without the prephosphate treat- ment are oiled (0.8 g m -2 ) and submitted to mechanical forming using a square hydraulic tool (20 cm × 20 cm) Roell–Korthaus KG as shown in Fig. 1a. Similar procedure had already been employed before [4,7]. 0300-9440/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0300-9440(02)00214-X