The corrosion inhibition of thermally pre-aged

Aluminium-Silicon-Magnesium (Al-Si-Mg) alloy in 3.5 %

NaCl solution with natural Avogadro oil of varying concentrations

has been studied using linear polarization

techniques. From the results obtained, the corrosion rate

decreased with an increase in Avogadro oil concentration.

An inhibitor efficiency of 46.7, 58 and 71 % were

obtained at 1.5, 3.0, 4.5 g/v Avogadro oil addition in a

3.5 % NaCl solution respectively for the conventional alloy.

Results from the linear polarization technique indicate a

higher potential value with an increase in the polarization

resistance (Rp) and lower current density in the inhibited

samples than the uninhibited Al-Si-Mg alloy as obtained

from the Tafel plot extrapolation. There exist some levels of

correlation in the inhibitor efficiency between the conventional

and the thermally pre-aged Al-Si-Mg alloy/Avogadro

oil in 3.5 % NaCl solution

Abdulwahab, M

Fayomi, O. S. I

Kasim, A.

Umaru, O. B.

Yaro, S. A.

Covenant University Repository

Silicon (2013) 5:225–228DOI 10.1007/s12633-013-9156-0ORIGINAL PAPEREffect of Avogadro Oil as Corrosion Inhibitor of ThermallyPre-aged Al-Si-Mg Alloy in Sodium Chloride SolutionM. Abdulwahab · A. Kasim · S. A. Yaro ·O. S. I. Fayomi · O. B. UmaruReceived: 13 March 2013 / Accepted: 17 June 2013 / Published online: 4 July 2013© Springer Science+Business Media Dordrecht 2013Abstract The corrosion inhibition of thermally pre-agedAluminium-Silicon-Magnesium (Al-Si-Mg) alloy in 3.5 %NaCl solution with natural Avogadro oil of varying con-centrations has been studied using linear polarizationtechniques. From the results obtained, the corrosion ratedecreased with an increase in Avogadro oil concentra-tion. An inhibitor efficiency of 46.7, 58 and 71 % wereobtained at 1.5, 3.0, 4.5 g/v Avogadro oil addition in a3.5 % NaCl solution respectively for the conventional alloy.Results from the linear polarization technique indicate ahigher potential value with an increase in the polarizationresistance (Rp) and lower current density in the inhibitedsamples than the uninhibited Al-Si-Mg alloy as obtainedfrom the Tafel plot extrapolation. There exist some levels ofcorrelation in the inhibitor efficiency between the conven-tional and the thermally pre-aged Al-Si-Mg alloy/Avogadrooil in 3.5 % NaCl solution.Keywords Avogadro oil · Inhibitor efficiency ·Aluminium alloy · Eco-friendly · Corrosion rateM. Abdulwahab () · A. Kasim · S. A. Yaro · O. B. UmaruDepartment of Metallurgical and Materials Engineering,Ahmadu Bello University,Zaria, Nigeriae-mail: mabdulwahab@abu.edu.ngM. Abdulwahab · O. S. I. FayomiDepartment of Chemical and Metallurgical Engineering,Tshwane University of Technology,Pretoria, South AfricaO. S. I. FayomiDepartment of Mechanical Engineering, Covenant University,Ota, Ogun State, Nigeria1 IntroductionCast Al-Si-Mg alloys have been widely used in the auto-motive and aircraft industries due to their good propertiesand high strength to weight ratio [1–8]. Some of theirattractive properties are good extrudability, relative highstrength, good corrosion resistance, excellent casting char-acteristics, light weight and acceptable cost [9–11]. Gen-erally, aluminium has higher corrosion resistance becauseof its thin surface oxide film formation. Although, in anaggressive environment, mostly chloride and acidic, the pro-tective films break down, however, the oxide coating is nottotally removed but is thinned and regenerated by the oxi-dation of the underlying metal [12]. Corrosion inhibitorsare needed to reduce the corrosion rates of metallic mate-rials in these environments [13]. An inhibitor is usuallyadded in small amount in order to slow down the rateof corrosion through the mechanism of adsorption [13].Some chemical and synthetic corrosion inhibitors such assodium benzoate that have been known to exhibit goodcorrosion resistance are not eco-friendly and create an envi-ronmental threat [12]. Therefore, efforts toward identifyingany potential eco-friendly and less expensive corrosioninhibitors remain relevant and progressive. The growinginterest among researchers for green inhibitors has remaineda top research focus [12]. In that direction, plant extracts andoils have gained acceptance as corrosion inhibitors that areconsidered safe, eco-friendly, available and less expensivefor most metals and alloys [14]. In our previous study [15],we considered the corrosion behavior of the pre-aged alloyin 3.5 % NaCl without the use of inhibitor. In this work, thepotential of natural Avogadro oil as corrosion inhibitor fora thermally pre-aged Al-Si-Mg alloy in NaCl solution havebeen investigated.226 Silicon (2013) 5:225–228Table 1 Chemical composition of the Al-Si-Mg alloy produced(wt %)Al Si Mg Fe Cu Mn Zn Ti Na92.14 7.0 0.3 0.08 0.03 0.03 0.03 0.03 0.012 Experimental Procedures2.1 Materials and Sample PreparationAl-Si-Mg alloy specimens of dimension 20 × 10 mm withchemical composition shown in Table 1 were used ascoupons for the corrosion study in 3.5 % NaCl solution. Ini-tially, the coupons were mechanically polished with emerypapers down to 600 grid sizes. The samples were degreasedin ethanol, dried, weighed and stored in a desiccator. Aconcentration of 3.5 % sodium chloride solution (NaCl)was prepared fresh as required for the experiment. Avo-gadro oil as inhibitor was used with NaCl salt solution. TheAvogadro natural oil was obtained from Technology Inno-vation Agency, Chemical Station, Ga-Rankuwa, TshwaneUniversity of Technology, Pretoria. The corrosion measure-ment was conducted at room temperature.2.2 Pre-ageing Thermal Treatment of Al-Si-Mg AlloyThe alloy produced was machined to a standard corrosioncoupon. The machined samples were solution heat treatedat a temperature of 540 ◦C for 1 h in an electrical furnaceand then rapidly quenched in warm water. The quenchedsamples were given double thermal ageing (DTAT) at a pre-ageing temperature of 90 ◦C for 3 h, and then finally agedat 180 ◦C for 2 h.2.3 Electrochemical Corrosion MeasurementThe potentiodynamic polarization was used to evaluate thecorrosion rate of the Al-Si-Mg alloy in NaCl solution withAvogadro oil as inhibitor. All electrochemical measure-ments were obtained using an Autolab frequency responseanalyzer (FRA) coupled to a potentiostat and connectedto a computer system as the source of data acquisition. Aglass corrosion cell kit with a platinum counter electrode,saturated Ag/Ag reference electrode and Al-Si-Mg alloysample as working electrode were used for the electrochem-ical study. The working electrode samples were positionedat the glass corrosion cell kit, leaving 1 cm2 surfaces in con-tact with the solution. Polarization tests were carried outin 3.5 % NaCl solution with and without Avogadro oil instatic solution using a potentiostat (Model: AuT71791 andPGSTAT 30) with a scan rate of 0.003 V/sec. From the Tafelcorrosion analysis, the corrosion rate, potential and linearpolarization resistances were obtained.3 Results and Discussion3.1 ResultsTable 2 shows the linear polarization corrosion data for Al-Si-Mg alloy in 3.5 % NaCl static solution with and withoutAvogadro oil addition. Figure 1 illustrates the linear polar-ization curves for Al-Si-Mg alloy in 3.5 % NaCl staticsolution with and without Avogadro oil addition while Fig. 2gives the comparism between inhibitor efficiencies and ther-mally treated Al-Si-Mg alloy for different concentrationsobtained using potentiodynamic polarization-corrosion rate(PP-CR), potentiodynamic polarization-corrosion current(PP-Icorr) and linear polarization resistance (LPR) as crite-ria. Figure 3 shows Langmuir isotherms for the adsorptionTable 2 Linear polarization corrosion data for Al-Si-Mg alloy in 3.5 % NaCl static solution with and without Avogadro oil addition at roomtemperatureSamples ba bc Ecorr, Ecorr, jcorr icorr (A) Corrosion rate Polarization E begin (V) E end (V)(V/dec) (V/dec) Calc (V) Obs (V) (A/cm2) (mm/year) resistance ()180/2h + 0.0Avo 0.052979 0.17701 −1.0426 −1.0166 3.49E-06 6.97E-06 0.032957 2539.4 −1.0727 −0.91156180/2h + 1.5Avo 0.050268 0.1354 −1.125 −1.1056 1.86E-06 3.73E-06 0.017612 4272.2 −1.1459 −1.0361180/2h + 3.0Avo 0.080537 0.15375 −0.86511 −0.83985 1.90E-06 3.79E-06 0.017935 6048.6 −0.87494 −0.74799180/2h + 4.5Avo 0.11159 0.23682 −1.0697 −1.0409 1.88E-06 3.76E-06 0.017757 8767 −1.1093 −0.8578590/3h + 0.0Avo 0.042124 0.17177 −1.1082 −1.0848 3.09E-06 6.18E-06 0.029225 2375.8 −1.1264 −0.9823690/3h + 1.5Avo 0.064052 0.13327 −1.3241 −1.3045 3.35E-06 6.69E-06 0.03162 2808.1 −1.3266 −1.236390/3h + 3.0Avo 0.070627 0.1166 −1.092 −1.074 2.89E-06 5.78E-06 0.027338 3302.4 −1.1264 −1.001990/3h + 4.5Avo 0.058124 0.19357 −1.0292 −0.9995 2.55E-06 5.11E-06 0.02412 3802.4 −1.0556 −0.89203Silicon (2013) 5:225–228 227Fig. 1 Linear polarization curves for Al-Si-Mg alloy in 3.5 %NaCl static solution with and without Avogadro oil addition at roomtemperatureof Avogadro oil compounds on Al-Si-Mg alloy in 3.5 %NaCl static solution.3.2 Discussion3.2.1 Potentiodynamic PolarizationIn the polarization measurement (see Table 2), linear polar-ization resistance was used as the criterion for the electro-chemical corrosion evaluation for Al-Si-Mg alloy in 3.5 %NaCl/Avogadro oil. In Fig. 1, the anodic and cathodic polar-ization curves for the Al-Si-Mg alloy in basic mediumAvogadro oil and uninhibited conditions were shown. It canbe seen that for samples that were given the conventionalageing treatment i.e 180 ◦C for 2 h, the current densitydecreased with an increase in inhibitor concentration andcorrosion potential (Ecorr) increased for 1.5, 3.0 and 4.5 g/vAvogadro oil additions, respectively (Fig. 1). From the lin-ear polarization resistance values, it shows that addition ofthe inhibitor resulted into an increase in the polarizationresistance (Rp) of the Al-Si-Mg alloy from 2539.4 (unin-hibited) to 8767 (inhibited) condition. The increase in Rpgenerally suggested an improvement in the corrosion resis-tance of the metal in the presence of the inhibitor. Thisshows that the metal is protected within the immersion timeconsidered. Considering the electrochemical corrosion forthe Al-Si-Mg alloy pre-aged at 90 ◦C for 3 h at 3.5 %NaCl-Avogadro oil (Fig. 1), a different trend in the corro-sion resistance were observed with an increase in corrosionrate for 1.5 g/v addition of Avogadro oil and a decrease incorrosion rate with 3.0 and 4.5 g/v inhibitor addition as com-pared with the uninhibited condition. Since both the anodicand cathodic branches change with the addition of inhibitorconcentrations, the natural Avogadro oil can be said to haveacted as a mixed-type corrosion inhibitor within the studiedenvironments.3.2.2 Inhibitor Efficiency and Adsorption BehaviorThe percentage inhibitor efficiency (% IE) of the Al-Si-Mgalloy-Avogadro oil in NaCl solution was computed usingthe equation reported [12]. The computed data for the IEusing potentiodynamic polarization-corrosion rate (PP-CR),potentiodynamic polarization-corrosion density (PP-Icorr),and linear polarization resistance (LPR) are presented inFig. 2 for NaCl/Avogadro oil. From the results, it showedthat % IE of the Avogadro oil increases with an increase inthe inhibitor concentrations. The reason being that, as theinhibitor concentration increases, the surface area coveredFig. 2 Comparism betweeninhibitor efficiencies andthermally treated Al-Si-Mg alloyfor different concentrationsobtained using potentiodynamicpolarization-corrosion rate(PP-CR), potentiodynamicpolarization-corrosion current(PP-Icorr) and linearpolarization resistance (LPR) ascriteria-20-1001020304050607080IE (%) Thermal treated Al-Si-Mg alloy  1.534.5228 Silicon (2013) 5:225–228Fig. 3 Langmuir isotherms forthe adsorption of Avogadro oilcompounds on Al-Si-Mg alloyin 3.5 % NaCl static solution atroom temperaturey = 2.1808x- 0.0228  R² = 0.9998 (180/2h+1.5Avo PP-CR ) y = 2.1831x- 0.032  R² = 0.9997 (180/2h+3.0Avo PP-Icorr) y = 0.8833x + 2.4167R² = 0.9955 (180/2h+4.5Avo LPR)y = 0.7533x + 8.5467R²= 0.9907 (90/3h+4.5Avo LPR)   024681012140 1 2 3 4 5C/θC (g/v)180/2h+1.5Avo PP-CR180/2h+3.0Avo PP-Icorr180/2h+4.5Avo LPR90/3h+4.5Avo LPRby this inhibitor increased. Hence, IE was enhanced sig-nificantly. It can be seen that the alloy with conventionalthermal treatment demonstrated better corrosion resistancethan those pre-aged prior to thermal treatment. From thisbehaviour, coupled with simultaneous change in the anodicand cathodic region during the electrochemical measure-ment Avogadro oil can be said to exhibit a mixed-typecorrosion inhibition. This occurrence agrees with previousreports [12, 14].The adsorption mechanism was shown from the variationbetween C/θ with C indicating linearity at room temper-ature for the environment (Fig. 3). The correction factors(R2) are approximately unity; PP-CR (0.9998), PP-Icorr(0.9997), LPR (0.9955), then, the adsorption behaviouris believed to have obeyed the Langmuir adsorptionisotherm.4 Conclusions1. Avogadro oil has been found to be a good corrosioninhibitor for a thermally pre-aged Al-Si-Mg alloy inNaCl solution at room temperature.2. The %IE and corrosion resistance of the thermallypre-aged Al-Si-Mg alloy increased with inhibitor con-centrations with higher IE in the conventionally treatedalloy.3. The best corrosion resistant alloy was found with thosetreated at 180 ◦C/2 h in 1.5 g/v Avogadro oil addition.4. The adsorption behavior of the Avogadro oil in basicmedia for Al-Si-Mg alloy can be said to have obeyedLangmuir adsorption isotherms and the oil acted as amixed-type inhibitor.Acknowledgments The authors appreciate with thanks the Depart-ment of Chemical and Metallurgical Engineering, Tshwane Universityof Technology, Pretoria for equipment support during the electrochem-ical corrosion test.References1. Kumar G, Hegde SB, Prabhu N (2007) J Mater Pro Tech 182:152–1562. Li YJ, Brusethaug S, Olsen A (2006) Scripta Mater 54:99–1033. Zhen L, Kang SB (1997) Scripta Mater 36(10):1086–10924. Sun Y, Baydogan M, Cimenoglu H (1999) Mater Lett 38:221–2265. Cerri E, Evangelista E, Spigarelli S, Cavaliere P, Dericcardis F(2000) Mater Sci Eng A 284:254–2606. Ma S, Maniruzzaman M, Mackenzie DS, Sisson RD (2006) Anenergy saving model for the heat treatment of castings. WorcesterPolytechnic Institute, Worcester7. Umaru OB (2009) The effect of ageing time on the tensile proper-ties of cast Al-2.1 %Si-0.7 %Fe-0.4 %Cr alloys. Final year project.Department of Metallurgical and Materials Engineering, AhmaduBello University, Zaria8. Dey S, Gunjan MK, Chattoraj I (2008) Corr Sci 50:2895–29019. Abdulwahab M, Madugu IA, Yaro SA, Popoola API (2011). MatDes 32:1159-116610. Svenningsen G, Larsen MH, Nordlien JH, Nisancioglu K (2006)Corr Sci 48:3969–398711. Wei BC, Chen CQ, Huang Z, Zhang YG (2005) Mater Sci Eng A280:161–16712. Popoola API, Fayomi OSI, Abdulwahab M (2012) J Electro Sci7:5817–582713. Benali O, Benmehdi H, Hasnaoui O, Selles C, Salghi R (2012)J Mater Env Sci 4(1):127–13814. Abdulwahab M, Kasim A, Fayomi OSI, Asuke F, Popoola API(2012) J Mater Env Sci 3(6):2028–250815. Umaru OB, Abdulwahab M, Yaro SA, Asuke F, Fayomi OSI(2013) Corr Sci (article submitted for publication), CORSCI-D-13-00317

Effect of Avogadro Oil as Corrosion Inhibitor of Thermally

Pre-aged Al-Si-Mg Alloy in Sodium Chloride Solution

http://eprints.covenantuniversity.edu.ng/9465/1/Silicon%20avogadro%20inhi.pdf

Effect of Avogadro Oil as Corrosion Inhibitor of Thermally Pre-aged Al-Si-Mg Alloy in Sodium Chloride Solution

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