Materials Chemistry and Physics 125 (2011) 628–640 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Corrosion inhibition of 6061 Al–15 vol. pct. SiC(p) composite and its base alloy in a mixture of sulphuric acid and hydrochloric acid by 4-(N,N-dimethyl amino) benzaldehyde thiosemicarbazone Geetha Mable Pinto a , Jagannath Nayak b , A. Nityananda Shetty a,∗ a Department of Chemistry, National Institute of Technology Karnataka, Surathkal, Srinivasnagar 575 025, Mangalore, Karnataka, India b Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Surathkal, Srinivasnagar 575 025, Karnataka, India article info Article history: Received 10 December 2009 Received in revised form 2 September 2010 Accepted 7 October 2010 Keywords: A. Alloys C. Electrochemical techniques D. Adsorption D. Corrosion abstract The corrosion inhibition characteristics of 4-(N,N-dimethylamino) benzaldehyde thiosemicarbazone (DMABT) on the corrosion behavior of 6061 Al–15 vol. pct. SiC(p) composite and its base alloy were studied at different temperatures in acid mixture medium containing varying concentrations of hydrochloric acid and sulphuric acid using Tafel extrapolation technique and ac impedance spectroscopy (EIS). The effect of inhibitor concentration, temperature and concentration of the acid mixture media on the inhibitor action was investigated. It was found that inhibition efficiencies increase with the increase in inhibitor concentration, but decrease with the increase in temperature and with the increase in concentration of the acid media. Thermodynamic parameters for dissolution process were determined. The adsorption of DMABT on both the composite and base alloy was found to be through physisorption obeying Freundlich adsorption isotherm. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Reinforcing 6061 Al alloy with SiC particles results in their better performance [1,2]. Aluminum matrix composites (AMCs) have received considerable attention for military, automobile and aerospace applications because of their low density, high strength and high stiffness [3–9]. One of the main drawbacks in the use of metal matrix composite is the decrease in corrosion resistance compared to the base alloy. For the base alloy, protective oxide sur- face film imparts corrosion resistance; but, addition of a reinforcing phase could lead to discontinuities in the film, thereby increasing the number of sites where corrosion can be initiated and making the composites more vulnerable [8,10]. However, the high corro- sion rates of these composites, particularly in acid media can be combated using inhibitors [11,12]. Due to the wide applications of such composites, they frequently come in contact with acid dur- ing cleaning, pickling, descaling, etc. The inhibition of aluminum corrosion in acid solutions was extensively studied using organic and inorganic compounds. It has been reported that the addition of chloride ions to sulphate solutions enhances aluminum corrosion [13]. A wide variety of compounds are used as inhibitors in acid media. These are mainly organic compounds containing N, S or O ∗ Corresponding author. Tel.: +91 824 2474200/9448779922; fax: +91 824 2474033. E-mail address: nityashreya@gmail.com (A.N. Shetty). atoms [14–16] and critical use of these compounds in industries has also been reviewed [17–19]. Organic compounds containing both N and S atoms function as better adsorption inhibitors because of their lone pair of electrons and polar nature of the molecules [20,21]. The present work aims at investigating the inhibitive action of 4- (N,N-dimethyl amino) benzaldehyde thiosemicarbazone (DMABT) on the corrosion of 6061 Al–15 vol. pct. SiC(p) composite and its base alloy in acid media containing hydrochloric acid and sulphuric acid at different concentration levels of the acids as well as at different temperatures. The investigations were carried out using electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Corrosion parameters were derived in the presence and absence of the inhibitor and inhibition efficiency was calculated in different acid mixture concentrations. 2. Experimental 2.1. Material The experiments were performed with specimens of 6061 Al–15 vol. pct. SiC(p) composite and its base alloy in extruded rod form (extrusion ratio 30:1). The com- position of the base metal 6061 Al alloy is given in Table 1. Cylindrical test coupons were cut from the rods and sealed with epoxy resin in such a way that the areas of the composite and the base alloy exposed to the medium were 0.95 cm 2 and 0.785 cm 2 , respectively. These coupons were polished as per standard metallographic practice, belt grinding followed by polishing on emery papers, and finally on polishing wheel using levigated alumina to obtain mirror finish. It was then degreased with acetone, 0254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2010.10.006