Corrosion Behavior of Al-Cu-Ni-Y alloys M.N.Derman 1, a, M.R. Jeffry 2, and R. Kumar 3,

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1 Advanced Materials Research Online: ISSN: , Vol. 795, pp doi: / Trans Tech Publications, Switzerland Corrosion Behavior of Al-Cu-Ni-Y alloys M.N.Derman 1, a, M.R. Jeffry 2, and R. Kumar 3, 1 Institutue of Nanoelectronic Engineering, Universiti Malaysia Perlis, Kangar, Perlis Malaysia 2,3 School of Materials Engineering, Universiti Malaysia Perlis, Taman Muhibbah, Jejawi Arau, Perlis Malaysia a nazree@unimap.edu.my (corresponding author) Keywords: Aluminium Alloy, Nickel, Corrosion and Copper. Abstract. Al based alloy has been widely used in various industries. This research paper aims at the investigation onto the effect of the percentage of Cu and Ni alloying elements in the corrosion behavior of Al-Cu-Ni alloys. The alloys were characterized by microstructural analysis, physical properties analysis, electrochemical analysis, and phase analysis. By observing the microstructure of the samples, it shows that the dendritic microstructures are occurs. The addition of Ni reveals columnar twinned dendritic to the longitudinal direction of cast ingots. While the addition of Cu increases the density of the sample. The Vickers microhardness test shows that the sample Al86- Ni5-Cu3-Y6 reached the optimum of the hardness value which is HV. Tafel Plot that performed shows that Al86-Ni5-Cu3-Y6 has the highest Polarization Resistance, Rp, kω and lowest corrosion rate, mm per year. An alloy with high Rp value is highly resistant to corrosion. Introduction Generally, many marine structures such as ship decks, cargo containers, sea platforms, piers etc are made of aluminium alloys because of their light weight and a high strength-to-weight ratio. These structures are exposed to sea water which is corrosive aqueous environment (chloride media). Marine corrosion is a constant issue for the marine industry. Based on studies, increase of the cost of marine corrosion has been estimated at 4% of the National Gross Product [1]. Numerous methods and precautions have been performed to reduce corrosion. One of the techniques is the addition of alloying elements. Thus, copper and nickel are used as alloying elements in this research. Copper improves the strength and hardness in the cast and also in heat treated conditions. Nickel increases the strength of high purity of aluminium. There are commonly added to Al-Cu alloys to improve the hardness and strength at elevated temperatures [2][3]. Al-Cu-Ni alloy are material which can exhibit high hardness, high corrosion resistance and high wear resistance. It is produced in low temperature processing to suppress nucleation growth of crystalline phase. However, the presences of both elements also influence the corrosion resistance of the alloys [4][5][6]. In this research, immersion of different percentage of Ni and Cu, Al-based alloy in neutral 3.5% sodium chloride solution method is proposed to study the corrosion behaviour of Al alloys. The aim of this research is investigate the effect of different percentage of copper and nickel on the corrosion behaviour of casting aluminium based alloy. Experimental Procedure Al-Ni-Cu alloy was fabricated by casting methods. The portions of aluminium, copper, nickel and yittrium were inserted into the graphite crucible and it was then placed into the furnace. This alloys was melt in melting furnace at 800 C using Ar gas,0.1% of sulphur hexafluoride (SF 6 ), together with 99.9% carbon dioxide (CO 2 ). The mixture molten metal was stirred in with a graphite rod for a complete solubility and cast into ceramic mould at 760 C, The mixture molten alloys was allowed for slow cooling in the oven at 420 C for 2 hours. Such procedures were performed to all the nine samples mentioned in Table 1 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-10/05/16,11:02:41)

2 E(V vs. ref) 536 2nd International Conference on Sustainable Materials (ICoSM 2013) Table1: Composition of samples Composition (Wt%) Element Al Ni Cu Y Al86-Cu8-Y Al86-Ni1-Cu7-Y Al86-Ni2-Cu6-Y Al86-Ni3-Cu5-Y Al86-Ni4-Cu4-Y Al86-Ni5-Cu3-Y Al86-Ni6-Cu2-Y Al86-Ni7-Cu1-Y Al86-Ni8-Y Corrosion testing is done using Tafel extrapolation testing. A special holder with 1 cm 2 area exposed was used to hold the sample and parts were immersed in 3.5% NaCl solution for 2 hours prior testing in order for the metal to stabilize in the electrolytic environment. Tafel extrapolation was performed on each Al-Cu-Ni alloy samples by Gamry G300 potentiostat/ galvanostat at room temperature. The resulting current density was plotted on a logarithmic scale. The corrosion current (i corr ) was obtained from a Tafel Plot by extrapolating the linear portion of the curve to E corr. As shown in Fig E-01 Graph of E vs Log current density -5.00E E E E E E E Log current density (A/cm2) Figure 1: Tafel plot of Al-Ni-Cu Alloy From the plotted graphs and data obtained (Fig. 2), corrosion rate of the samples can be calculated by using following eq 1. Where,CR refers as Corrosion rate. The i corr indicates to corrosion current in Ampere. The constant use as K with 3272 mm/ampere per year. E w indicates the equivalent weight in grams, Density and exposed aera was indicated by ρ (g/cm 3 ) and A(cm 2 )[7]. All samples was characterised microstrcuture using Olympus BX41M Metallurgical Microscope. (1)

3 Advanced Materials Research Vol Result and Discussion Metallographic examination is performed on all as-cast Al-Cu-Ni alloys. Figure 1 compares the microstructures of the alloys with different Cu and Ni contents. Microstructure of Al86-Cu8-Y6 in Figure 4.1 (a) shows clearly defined equiaxed grains. While, other microstructures show finer grains which are dendritic. The dendritic grain structure is very common in metal castings and generally due to pile up ahead of the growing solid during solidification especially when liquid metal is undercooled [8]. (a) (b) (c) (d) (e) (f) (g) (h) (i) Figure 2: Microstructure of as-cast Al-Cu-Ni alloys at magnification 100 X (a) Al86-Cu8-Y6 (b) Al86-Ni1-Cu7-Y6 (c) Al86-Ni2-Cu6-Y6 (d) Al86-Ni3-Cu5-Y6 (e) Al86-Ni4-Cu4-Y6 (f) Al86-Ni5-Cu3-Y6 (g) Al86-Ni6-Cu2-Y6 (h) Al86-Ni7-Cu1-Y6 (i) Al86-Ni8-Y6. Tafel extrapolation is used to determine the corrosion rate of Al samples. E corr in this case, is the rest potential, i.e., when there is no external potential is applied to the system. At E corr, the oxidation of metal and reduction of the species in the solution is taking place at the same rate where the net measureable current is zero. While, i corr is the current density at E corr representing the total of the oxidation current and reduction current that is in equilibrium. These two parameters contributed to the measurement of corrosion rate in Tafel extrapolation. Besides, corrosion current density (i corr ), corrosion potential (E corr ), polarization resistance (R p ) and corrosion rate measured by the Tafel extrapolation were calculated and presented in Table 2.

4 538 2nd International Conference on Sustainable Materials (ICoSM 2013) Table 2: E corr, i corr, corrosion rate and polarization resistance of Al-Cu-Ni alloys in NaCl solution. Al alloys E corr (V) i corr (A/cm 2 Corrosion rate Polarization ) (mm per year) Resistance (kω) Al86-Cu8-Y Al86-Ni1-Cu7-Y Al86-Ni2-Cu6-Y Al86-Ni3-Cu5-Y Al86-Ni4-Cu4-Y Al86-Ni5-Cu3-Y Al86-Ni6-Cu2-Y Al86-Ni7-Cu1-Y Al86-Ni8-Y From the Table 2, the presence of Ni element in Al-Cu-Y system causes E corr to be shifted more towards negative. On the other hand, the presence of Cu element in Al-Ni-Y system causes E corr to be shifted more towards positive. Al86-Cu8-Y6 is found to exhibit most positive E corr and highest i corr. However, increasing Ni content particularly is found to increase the corrosion rate of Al-Cu-Y alloys. From Table 4.3 and Figure 4.4, Al86-Ni7-Cu1-Y6 shows greater corrosion rate than Al86-Ni1-Cu7-Y6. Impurities and cathodic additives such as Fe, Ni and Cu depend on the content may increase the susceptibility to pitting [9]. The lowest corrosion rate was portrays by Al86-Ni2-Cu6-Y6 which is at mm per year. While the corrosion rate of Al86-Ni7-Cu1-Y6 obtained is mm per year which is the highest among other studied samples [10]. Conclusion The percentage of Cu and Ni content in Al-Cu-Ni alloys were greatly influences the physical properties and corrosion behavior of the alloy. The effect of different Cu and Ni content in the alloy is studied and the findings that both Ni and Cu in the alloy with different percentage shows a significant effect on the corrosion rate of the alloy. Sample Al86-Ni2-Cu6-Y6 has the lowest corrosion rate which is mm per year, while sample Al86-Ni7-Cu1-Y6 has the highest corrosion rate, mm per year. Acknowledgements This work was financially supported by the Fundamental Research Grant (FRGS ) Ministry of Higher Education Malaysia and Universiti Malaysia Perlis (Seed Money Grant)

5 Advanced Materials Research Vol References [1] Wan Nik, W. B., Sulaiman, O., Fadhli, A., and Rosliza, R., Corrosion Behaviour of Aluminium Alloy in Seawater. Proceedings of MARTEC 2010 (2010), pp [2] Hong, S. J., Warren, P. J., & Chun, B. S., Nanocrystallization behaviour of Al Y Ni with Cu additions, Materials Science and Engineering: A, Volume , (2001), p [3] Kaufman, J. G., and Rooy, E. L., Aluminium Alloy Casting: Properties, Processes, and Applications, ASM International, USA. (2004) [4] Davis, J. R., Corrosion of Aluminium and Aluminium Alloys. ASM International, USA. (2000) [5] Hollingsworth, E.H. and Hunsicker, H.Y. Aluminium Alloys, In: Corrosion and Corrosion Engineering, 2nd Edition, Schweitzer P.A. [editor], Marcel Dekker, New York. (1998). [6] Kamarudin, S.R.M., Daud, M., Muhamad, A., Sattar, M.S., and Daud, A.R. Corrosion Behaviour of Al Alloys in Sea Water, AIP Conference Proceeding(2010) pp [7] Scully, J. R. (2005). Electrochemical Tests. In: Corrosion Tests and Standards: Application and Interpretation - Second Edition, 2 nd Edition, Baboian, R. [editor], ASTM International, Baltimore, MD.(2005) [8] Shehzad, B., Khan, S., Hort, N., Eiken, J., & Steinbach, I., Numerical Determination of Heat Distribution and Castability Simulations of as Cast Mg---Al Alloys **. Advanced Engineering Materials, (3),(2009) pp [9] Sinyavskii, V. S., and Kalinin, V. D., Marine Corrosion and Protection of Aluminium Alloys According to Their Composition and Structure. Protection of Metals, 41(4),(2004) pp [10] Schweitzer, P. A., Fundamental of Metallic Corrosion: Atmospheric and Media Corrosion of Metals. 2nd Edition, CRC Press, USA.(2007)

6 2nd International Conference on Sustainable Materials (ICoSM 2013) / Corrosion Behavior of Al-Cu-Ni-Y Alloys /