Structural investigation of the zirconium-titanium based amino trimethylene phosphonate hybrid coating on aluminum alloy

Transcription

1 Acta Metall. Sin.(Engl. Lett.)Vol.22 No.3 pp June 2009 Structural investigation of the zirconium-titanium based amino trimethylene phosphonate hybrid coating on aluminum alloy Shuanghong WANG 1), Changsheng LIU 1) and Fengjun SHAN 1,2) 1) Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 14, China 2) Material & Chemical Engineering College, Liaoning University of Technology, Jinzhou , China Manuscript received 8 January 2008; in revised form 16 May 2008 A zirconium-titanium based amino trimethylene phosphonate hybrid coating on AA6061 aluminum alloys was formed by dipping in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid (ATMP) solution for improving the lacquer adhesion and corrosion resistance as a substitute of chromate coatings. The morphology and structure of the hybrid coating were studied by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface composition and structure characteristics were also investigated by means of X-ray photoelectron spectroscopy (XPS) and Fourier transformation infra-red spectroscopy (FTIR). The results of SEM and AFM show that the hybrid coating present piece particle distribution which is much denser than that of the zirconium-titanium coating. The results of XPS and FTIR indicate that the hybrid coating is a hybrid composite structure composed of both the zirconium-titanium and amino trimethylene phosphonate coatings. KEY WORDS Fluorotitanate/fluorozirconate; Amino trimethylene phosphonic acid; Hybrid coating; Aluminum alloys; Corrosion resistance 1 Introduction Chromium conversion coatings have been applied successfully to aluminum and aluminum alloys to improve corrosion resistance and adhesion to the lacquer for a long time. However, the need for nontoxic and environmentally friendly processes has led to the development of various chromate-free alternatives during the metal pretreatment. The majority of chromate-free alternatives currently in use are Ti and/or Zr oxide based and sometimes also incorporates a polymer to promote adhesion [1 5]. Recently, the alkylphosphonic acid, as inhibitors, is applied extensively in several areas of technology, such as chemical water treatment for deposit prevention and control [6]. The alkylphosphonic acid can react chemically and/or physically with the metal surface and simultaneously form a covalent phosphorous-oxygen-carbon (P-O-C) linkage with the polymer resin, improv- Corresponding author. PhD; Tel.: address: w.shuanghong@163.com (Shuanghong WANG) DOI: /S (08)84-8

2 162 ing coating adhesion and corrosion resistance [7]. Shida et al. [8] indicated that the selfassembled zirconium-phosphate derivative films effectively protected aluminum substrates. In particular, the multilayered zirconium-phosphate film fabricated by adsorbing 1,12- dodecyldiphosphonic acid has shown superior anticorrosion properties to Al1100. In this article, we used SEM and AFM to study the morphology and structure of zirconium-titanium based amino trimethylene phosphonate hybrid coating formed by dipping in a fluorotitanate/zirconate acid and ATMP solution. XPS and FTIR were also used to analyze surface composition in order to replace chromate treatments for the protection of aluminum alloys. 2 Experimental All the reagents used were of reagent grade quality and substances were obtained from commercial sources. The AA6061 sheets from aluminum wheels were cut into pieces of 10 mm 10 mm 1.5 mm. The sheets were treated by milling with SiC paper to grade. The surfaces were carefully cleaned using ethanol and water prior to treatment. The forming process of conversion coating was carried out in the following manner: 1) Degreased in alkaline solution (2% NaOH) for 30 s at room temperature and rinsed in tap water. 2) Etched for 1 min by immersing in acid picking solution (0.01% HF and 1% H 2 SO 4 ) at room temperature and rinsed thoroughly using distilled water. 3) Zirconium-titanium based amino trimethylene phosphonate hybrid coating formed by immersing in the conversion bath for 120 s at 45 C. The conversion bath was prepared based on 40% fluotitanic, 45% fluozirconic acid and 50% aqueous ATMP. The conversion bath mainly contained 0.065% Ti, 0.024% Zr, 0.186% F and 0.08% ATMP. The ph value of the solution was adjusted to 3.5 with ammonia. 4) Rinsed in distilled water and dried for 30 min in an air circulation furnace at 100 C. The microstructures were characterized by AFM (Shimadzu SPM-9J2 system), SEM (Hitachi SSX-), XPS and FTIR (Bio-Rad FTS3000). 3 Results and Discussion Fig.1 shows SEM micrograph of the coating formed by immersing in zirconium-titanium Fig.1 SEM micrographs without (a) and with (b) ATMP.

3 163 bath without and with ATMP. The coating appears to be spherical particle deposition (Fig.1a). However, the zirconium-titanium based amino trimethylene phosphonate hybrid coating appears to be piece particle distribution (Fig.1b). Fig.2 shows AFM topographies indicating the presence of a number of nanosized particles in both coatings. It can be seen that the zirconium-titanium based amino trimethylene phosphonate hybrid coating is much denser than that of the zirconium-titanium coating. Fig.2 AFM topography without (a) and with (b) ATMP. Fig.3 shows FTIR spectra of the hybrid coating on aluminum alloy. The absorption peaks are observed at 860 cm 1 for Ti 4+ and at 830 cm 1 for thermally oxidized Zr. The broad absorption between 1750 and 2000 cm 1 is a characteristic absorbance of aluminum surfaces treated with H 2 ZrF 6 [9]. Thus, the zirconium-titanium coating has been assumed to be presence on the surface. The compounds with the P-OH groups have two bands of the OH-stretching vibration in the wavenumber regions ranging from 2700 to 2 cm 1 and from 2300 to 2100 cm 1 at medium to small intensities, respectively. Further characteristic bands of the phosphonic acid are due to associated P=O stretching vibrations at cm 1, and broad absorbance peaks at cm 1 can be assigned to symmetric and asymmetric valence bands of salts of alkylphosphonic groups [10]. However,

4 164 the appearance of two CH 2 signals are at 2925 and 1852 cm 1, corresponding to the symmetric and asymmetric CH 2 stretching modes. So, the results of FTIR spectra show that both the zirconium-titanium and the amino trimethylene phosphonate hybrid coatings existed on the surface of aluminum alloy. The XPS survey spectra are shown in Fig.4. Corresponding peak positions and atomic concentrations based on the curve fitting are listed in Table 1. It shows the notable characteristic peaks for Al, C, F, N, O, P, and Ti, whereas Zr is barely confirmed because binding energy of Zr3d is close to that of P2s. The XPS single scanning spectra corresponding to the elements are shown in Fig.5. The Al2p peak (Fig.5a) is curvefitted two different peaks representing two different oxygen species. Binding energy at 73.4 ev corresponds to Al oxide and ev for AlF 3 H 2 O referring to NIST Database. The C1s spectrum (Fig.5b) shows three significant peaks of different binding energies at Transmittence (P-C) Ti 4+ H 2 ZrF C-N 6 (P=O) P-OH ass Oxidized Zr (PO 2- ) a 3 2- ) (H O) (P=O) sci 2 as 3 sci (CH ) s 2 (CH ) as 2 (CH ) sci 2 (O-H) Wave numbers / cm -1 Fig.3 FTIR spectra of the hybrid coating on aluminum alloy Al 2p Al 2s P 2p Zr 3d+P 2s C 1s N 1s Ti 2p O 1s F 1s F KLL O KLL Fig.4 XPS survey spectra of the hybrid coating on aluminum alloy. Table 1 Compositions of the hybrid coating on aluminum alloy Elements (xps) Assignments Zirconium-titanium based ATMP hybrid coating BE/eV FWHM/eV at. pct Al(2p) Al 2 O AlF C(1s) C CH C-N F(1s) ZrF AlF 3 H 2 O N(1s) N-C NH O(1s) Oxide Phosphonate P=O P-OH P(2p) P-O-Metal CH 2P(O)(OH) Phosphonate Ti(2p) TiO TiO Zr(3d) ZrO ZrO 2, ZrF

5 (a) Al 2 O 3 Al 2p AlF 3 H 2 O (b) C 1s CH 2 C C-N (c) ZrF 4 AlF 3 H 2 O F 1s (d) N-C -NH 2 N 1s (e) Phosphonate Oxide P-OH P=O O 1s (f) CH 2 P(O)(OH) 2 P-O-Metal P 2p Phosphonate (g) Ti 2p 1400 TiO (h) Zr 3d ZrO ZrO 2 or ZrF Fig.5 XPS single scanning spectra of the hybrid coating corresponding to the elements of Al (a); C (b); F (c); N (d); O (e); P (f); Ti (g); and Zr (h).

6 , and ev. Binding energy at ev corresponds to C referring to NIST Database and ev corresponds to CH [11] 2. The value of ev is closest to C-N (Amine: 286 ev, KCN: ev, and CH 3 CN: ev) corresponding to N(CH 2 ) 3 - of ATMP molecule structure. The F1s peak (Fig.5c) is curve-fitted two peaks at ev for ZrF 4 and ev for AlF 3 H 2 O. The N1s (Fig.5d) is curve-fitted two peaks at about ev and most likely to C-N. The O1s signal (Fig.5e) is curve-fitted into four different peaks. Binding energy of ev is close to Al oxide referring to NIST Database. The value of ev corresponds to metal phosphonate [12] and ev for P=O and ev for P-OH [12]. The P2p spectrum (Fig.5f) shows three significant peaks of the phosphonate group at , , and ev. Binding energy of ev corresponds to P-O-Metal [12] ; the value of ev is most likely CH 2 P(O)(OH) 2 referring to CH 3 P(O)(OH) 2 in NIST Database; and ev corresponds to the metal phosphonate [12]. In Ti2p peak (Fig.5g), binding energies of and ev for the Ti 2p3/2 and Ti 2p1/2 peaks, respectively, indicate that Ti is most likely Ti 4+ (TiO 2 ). The Zr3d curve-fitted peaks (Fig.5h) at about ev for Zr 3d5/2 and ev for Zr 3d3/2 peaks, respectively, indicate that Zr is likely ZrO 2 or ZrF 4. So, the results of XPS show that the zirconium-titanium based amino trimethylene phosphonate hybrid coating on aluminum alloy is a hybrid composite structure composed of both the zirconium-titanium and the amino trimethylene phosphonate coatings. 4 Conclusion A zirconium-titanium based amino trimethylene phosphonate hybrid coating on AA6061 aluminum alloys can be formed by dipping in a fluorotitanate/fluorozirconate acid and ATMP solution. The morphology and structure of the hybrid coating studied using SEM and AFM show that the hybrid coating appears to be particle distribution which is much denser than that of the zirconium-titanium coating. The results of XPS and FTIR indicate that the hybrid coating is a hybrid composite structure composed of both the zirconiumtitanium and the amino trimethylene phosphonate coatings. Acknowledgements This study was supported by the Science and Technology Plan Project of Liaoning Province, China (No ). REFERENCES [1] I. Paloumpa, A. Yfantis, P. Hoffmann, Y. Burkov, D. Yfantis and D. SchmeiBer, Surf Coat Technol (2004) 308. [2] O. Lunder, C. Simensen, Y. Yu and K. Nisancioglu, Surf Coat Technol 184 (2004) 278. [3] M.A. Smit, J.A. Hunter, J.D.B. Sharman, G.M. Scamans and J.M. Sykes, Corros Sci 45 (2003) [4] J.H. Nordlien, J.C. Walmsley, H. Østerberg and K. Nisancioglu, Surf Coat Technol 153 (2002) 72. [5] H. Vennschott, U. Karmashek and A. Roland, US Patent US (17 December 1996). [6] K.D. Demadis and P. Baran, J Solid State Chem 177 (2004) [7] T.L. Chhiu, Prog Org Coat 42 (2001) 226. [8] A. Shida, H. Sugimura, M. Futsuhara and O. Takai, Surf Coat Technol (2003) 686. [9] P.D. Deck, M. Moon and R.J. Sujdak, Prog Org Coat 34 (1998) 39. [10] I. Maege, E. Jaehne, A. Henke, H.P. Adler, C. Bram, C. Jung and M. Stratmann, Prog Org Coat 34 (1998) 1. [11] M. Textor, L. Ruiz, R. Hofer and A. Rossi, Langmuir 16 (2000) [12] R. Hofer, M. Textor and N.D. Spencer, Langmuir 17 (2001) 4014.