Emirates Journal for Engineering Research, 14 (1), 47-52 (2009) (Regular Paper)
INVESTIGATION OF COPPER ADDITION ON THE MECHANICAL PROPERTIES AND CORROSION RESISTANCE OF COMMERCIALLY PURE ALUMINUM A.E. Al-Rawajfeh and S.M.A. Al Qawabah Tafila Technical University, PO Box 179, 66110 Tafila, Jordan Email:
[email protected]
(Received December 2008 and accepted April 2009)
األلمنيوم ومعظم سبائكه تتجمد على شكل حبيبات كبيرة في غياب المنعمات والتي تؤدي إلى انخفاض الخصائص ، في ھذا العمل تم دراسة تأثير إضافة النحاس إلي األلمنيوم النقي على البنية المجھرية،الميكانيكية وجودة السطح ولقد تم تحضير ثالثة عينات من. الخصائص الميكانيكية ومقاومة التآكل، طاقة الصدم، حجم الحبيبات،الصالدة نحاس وتم دراستھا ميكانيكا وكيميائيا حيث أدت الزيادة في النحاس%9 ،%6 ،%3 النحاس بنسب-سبيكة األلمنيوم إلي زيادة خطية في الصالدة وانخفاض قليل في المتانة والى تنعيم ملحوظ في الحبيبات وتحسن في الخصائص الخصائص الميكانيكية ومقاومة التآكل كانت، الخصائص المختلفة من مقاومة الصدم.الميكانيكية ومقاومة التآكل . نحاس الى االلمنيوم%6 االفضل عند اضافة نسبة Aluminum and its alloys normally solidify in columnar structure with large grain size which results in deterioration of their surface quality and mechanical strength. In this work, the influence of Cu addition to commercially pure aluminum on microstructure, microhardness, grain size, impact energy, flow stress at 0.2 strain, mechanical behavior and corrosion resistance was studied. Three different Al-Cu alloys of 3,6 and 9 wt.% Cu content were prepared and experimentally tested both mechanically and chemically. The addition of Cu resulted in a linear increase of the hardness, and substantial reduction in the grain size, slight reduction the impact energy, substantial increase in the flow stress at 0.2 strains, and improve in the mechanical characteristics. The Potentiostatic measurements showed that the susceptibility of the samples towards corrosion decreases in the order: Al>Al-3 wt% Cu>Al-9 wt% Cu>Al-6 wt% Cu. The corrosion rates of the 3,6 and 9 wt% Cu alloys in HCl were found to be 0.29, 0.13 and 0.21 nm/s, respectively. The different properties, i.e. impact energy, flow stress at 0.2 strain, mechanical characteristics and corrosion resistance, showed that the 6 wt. % Cu is an optimal composition. Keywords: Aluminum, Copper, Mechanical properties, Corrosion, Potentiostatic polarization.
1. INTRODUCTION Aluminum is the second widely used metal due to its desirable chemical, physical and mechanical properties and it represents an important category of technological materials[1]. Due to its high strength-toweight ratio, besides other desirable properties e.g. desirable appearance, non-toxic, non-sparking, nonmagnetic, high corrosion resistance, high electrical and thermal conductivities and ease of fabrication, aluminum and its alloys are used in a wide range of industrial applications for different aqueous solutions. These properties led also to the association of aluminum and its alloys with transportation particularly with aircraft and space vehicles, construction and building, containers and packaging and electrical transmission lines.
All strengthening techniques rely on simple principal; restricting or hindering dislocation motion which renders the material harder and stronger. The strengthening mechanisms can be introduced by solid solution, strain hardening, precipitation hardening and grain size reduction. Fine grain size is often desired for high strength. Fine particles may be added to increase strength and phase transformations may also be utilized to increase strength[2]. Mechanical properties of Al-Cu alloys depend on copper content. Copper is added to aluminum alloys to increase their strength, hardness, fatigue and creep resistances and machinability. The first and most widely used aluminum alloys were those containing 4-10 wt. % Cu. On the other hand Al-Cu alloys, among the main aluminum alloys, have the lowest negative potential of corrosion[3]. Copper is being used, because it is one of
47
A.E. Al-Rawajfeh and S.M.A. Al Qawabah
the few elements that have relatively high solubility in Al. Thus, the product has an Al(Cu) solid solution matrix that is mechanically tougher than a pure Al matrix[4]. All metals and alloys undergo corrosion, which is defined as the destructive attack of a metal by the environment, by chemicals, or electrochemical processes. The driving force is the free energy of reaction of the metal to form, generally, a metal oxide. Since corrosion reactions generally occur on the metal surface, they are called interfacial processes. The corrosion process takes place at the metal medium phase boundary and therefore is a heterogeneous reaction in which the structure and condition of the metal surface have a significant role. The corrosive medium must be transported to the surface and the corrosion products removed. Therefore, material transport phenomena, including free convection and diffusion into adjacent surface layers, must also be taken into account[5]. Metallurgical factors that can affect corrosion in an alloy include: crystallography, grain size and shape, grain heterogeneity, impurity inclusions, and residual stress due to cold work. Mathiesen and Arnberg reported results on structure evolution in Al-Cu alloys during columnar growth[6]. Their results indeed showed significant coarsening of dendrite arms accompanied by dissolution and fragmentation during primary solidification. It will be quite exciting to employ this technique further in the study of coarsening kinetics, since the conventional solidify-and-quench technique can only produce the final microstructure, and cannot show the solidification process. The coarsening exponent is expected to depend on the cooling rate, but the exact dependence has not been clearly established[7]. The electrochemical behavior of Al-4.5 wt.% Cu alloy solidified under unsteady-state heat flow conditions were studied[8]. The microstructural pattern and the solute redistribution play an important role on the corrosion behavior. Al2Cu solidified under fast cooling conditions yielded a corrosion rate of about 10 times higher than pure aluminum in a 0.5M NaCl solution at 25oC. Although the Al2Cu particles have presented a higher corrosion potential than the Al-rich phase, its corrosion rate is also higher. However, the solid solution binary Al-(0.2-1%) Cu alloys exhibited severe filiform corrosion (FFC)[9]. The detrimental effect of copper in solid solution is attributable to selective dissolution phenomena during the corrosion process, whereby copper was locally enriched on the surface as copper-rich particles providing efficient cathodic sites. The relationship between solidification parameters and the microstructural parameters were investigated in four different Al-(3,6,15,24) wt.% Cu master alloys[10]. Most experimental studies have shown that the microstructural parameters decrease as solidification parameters increase, for the constant initial solute composition. The influence of nitric acid on corrosion of the AlCu alloys, containing 1.3-30 at.% Cu, were studied[11].
48
The corrosion rates of the Al-1.3 at.% Cu and Al-2.7 at.% Cu alloys in nitric acid were found to be ~5 and 10 nm min−1 respectively. The corrosion of an Al-30 at.% Cu alloys was less uniform, with a local rate to ~13 nm s−1. Amin et. al[12] have studied the pitting corrosion of ClO4- on pure Al, Al-2.5 wt% Cu and Al7 wt% Cu alloys in 1.0M Na2SO4 solution at 25 ◦C. The susceptibility of the three Al samples towards pitting corrosion decreases in the order: Al>Al-2.5 wt% Cu>Al-7 wt% Cu. Potentiostatic measurements showed that the rate of pitting initiation increases with increasing ClO4- ion concentration and applied step anodic potential, while it decreases with increasing Cu content. The corrosion behavior of pure Al, Al-6% Cu and Al-6% Si alloys in Na2SO4 solutions in the absence and presence of NaCl, NaBr and NaI were studied[13]. The corrosion resistance increases in the order AlAl-9 wt% Cu>Al-6 wt% Cu.
12.
13.
14.
15.
Acknowledgement We would like to thank Dr. Ehab Al Shamaileh, at the University of Jordan, for the potentiostatic polarization measurements.
REFERENCES 1. 2. 3. 4.
5.
52
Polmear, I.J. (1980). Light Alloys, Metallurgy of the Light Metals, 2nd edition, Arnold, London. Rollasaon, R. (1973). Metallurgy for engineers, 4th Edition, Edward Arnold, Great Britain. Rooy, E.L. (1988). Metals Handbook, 15, ASM International, Materials Park, Ohio, 743. Aravind, M., Yu, P., Yau, M.Y. and Ng, D.H.L. (2004). Formation of Al2Cu and AlCu intermetallics in Al(Cu) alloy matrix composites by reaction sintering. Materials Science and Engineering A380 384-393. Ullman’s Encyclopedia of Industrial Chemistry, B1, Ch.8, 2.
16.
17.
18.
19.
20.
Mathiesen, R.M. and Arnberg, L. (2005). X-ray radiography observations of columnar dendritic growth and constitutional undercooling in an Al30wt%Cu alloy. Acta Mater. 53, 947-56. Du, Q., Eskin, D.G., Jacot, A. and Katgerman, L. (2007). Two-dimensional modelling and experimental study on microsegregation during solidification of an Al-Cu binary alloy. Acta Materialia 55, 1523-1532. Os´orio, W.R., Spinelli, J.E. and Ferreira, I.L. (2007). A. Garcia; The roles of macrosegregation and of dendritic array spacings on the electrochemical behavior of an Al-4.5 wt.% Cu alloy Electrochimica Acta 52, 3265-3273. Afseth, J.H., Nordlien, G.M. and Scamans, K. (2002). Nisancioglu; Filiform corrosion of binary aluminium model alloys. Corrosion Science 44, 2529-2542. Gunduz, M. and Cadirli, E.C. (2002). Directional solidification of aluminium-copper alloys Materials Science and Engineering A327, 167-185. Liu, Y. and Arenas, M.A. (2008). A. de Frutos; J. de Damborenea; A. Conde; P. Skeldon; G.E. Thompson; P. Bailey; T.C.Q. Noakes; Influence of nitric acid pre-treatment on Al-Cu alloys. Electrochimica Acta 53, 4454-4460. Amin, M.A., Abd El Rehim, S.S., Moussa; S.O. and Ellithy, A.S. (2008). Pitting corrosion of Al and AlCu alloys by ClO4- ions in neutral sulphate solutions. Electrochimica Acta 53, 5644-5652. Abdel Rehim, S.S., Hassan, H.H. and Amin, M.A. (2002). Corrosion and corrosion inhibition of Al and some alloys in sulphate solutions containing halide ions investigated by an impedance technique Applied Surface Science 187, 279-290. Abdollah-Zadeh, Saeid, T. and Sazgari, B. (2008). Microstructural and mechanical properties of frictionstir welded aluminum/copper lap joints. Journal of Alloys and Compounds 460, 535-538 Os´orio, W.R., Spinelli, J.E., Freire, C.M.A. and Cardona, M.B. (2007). Amauri Garcia; The roles of Al2Cu and of dendritic refinement on surface corrosion resistance of hypoeutectic Al-Cu alloys immersed in H2SO4. Journal of Alloys and Compounds 443, 87-93. Talamantes-Silva, M.A., Rodríguez, A., TalamantesSilva, J., Valtierra, S. and Colás, R. (2008). Characterization of an Al-Cu cast alloy. Material characterization, doi:10.1016/j.matchar.2008.01.005. Man, J., Jing, L. and Jie, S.G. (2007). The effects of Cu addition on the microstructure and thermal stability of an Al-Mg-Si alloy Journal of Alloys and Compounds 437, 146-150. Geng, H., Wu, X., Wang, H. and Min, Y. (2008). Effects of copper content on the machinability and corrosion resistance of martensitic stainless steel. J. Mater. Sci. 43, 83-87. Giggins, C.S. and Pettit, F.S. (1969). The effect of alloy grain size and surface deformation one of the selective oxidation of chromium in nickel-chromium alloys at temperatures of 900oC and 1100oC”. Trans. TMS-AIME 245, 2509-2516. Arzt, E. and Singer, R.F. (1984). Proceedings of the Seven Spring Conference on Superalloys, The Metallurgical Society of AIME, 367-376.
Emirates Journal for Engineering Research, Vol. 14, No.1, 2009
