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Corrosion of Aluminum and Its Alloys

Authors:
in "Handbook of Aluminum, Vol. 2,
Alloy Production and Materials Manufacturing,"
G.E. Totten and D.S. MacKenzie, editors
... The corrosion of many Al alloys has been investigated previously to understand the mechanisms of corrosion and corrosion resistance. Typically, Al and its alloys undergo pitting corrosion in the presence of chlorine ions (Cl -) in which local breakdown of the metal-oxide passivation layer results in the dissolution of the Al surface [2][3][4][5][6]. Such pitting corrosion is of major concern due to the high Cllevels found in the environments in which these metals are typically used, such as in seawater and on roadways. ...
... Such pitting corrosion is of major concern due to the high Cllevels found in the environments in which these metals are typically used, such as in seawater and on roadways. For Al alloys, chromate conversion coating is commonly used to protect the surface [3]. However, this process involves the use of chromic acid which is toxic and highly regulated. ...
... Compositional differences within Al alloys are commonly observed due to secondary phase formation and as a result of processing, such as during heat treatments, aging, and welding [3,38,39]. Due to the high temperature, electrical current, and voltage used to manufacture the covetic samples it is extremely likely that similar changes in the local composition of the alloy have occurred for the covetic samples. Furthermore, the processing of the material with addition of carbon induces changes in corrosion potential, mechanical strength, and hardness. ...
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The recent invention of a new processing method for metals and alloys involving the addition of carbon has led to several reports demonstrating an enhancement in the mechanical properties of the materials known as “covetics.” In this work the corrosion behavior and mechanical properties of a 6061 aluminum–carbon covetic are investigated and explained. Covetic samples with carbon added were found to exhibit a corrosion potential 40–70 mV higher than samples processed without the addition of carbon. However, the corrosion current density of the covetic with carbon added relative to samples without carbon added was also increased. Surface characterization following the corrosion testing using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction revealed significant differences between the covetic with carbon added and the covetic parent material processed without carbon addition. After corrosion, the surface of the covetic with carbon added showed a alloying element rich surface morphology from the parent alloy and exhibited a smaller grain size than the material processed without carbon. Additionally, changes in the mechanical properties of the covetic were observed with both the hardness and the compressive strength of the covetic increasing as a result of carbon addition. The observed change in corrosion behavior and mechanical properties of the covetic with carbon added, along with the physical characterization, are consistent with the formation of a secondary phase in the alloy induced by carbon addition during the process used to make the covetic.
... Introduction Due to its light weight, simple workability, toughness, conductivity and tensile strength, Alu minum is one of the most favored metals in the manufacturing fields, it is very suitable for the construction of automobiles and aircraft components [1][2][3]. Aluminum as a metal is very prone to corrosion, corrosion has a negative effect on metals [4][5][6]. Corrosion inhibitor which are chemical compounds has proven to be effective in the protection of metals from corrosion [7][8][9]. ...
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The inhibitive effect of zinc oxide on the corrosion of aluminum in 2 M HCl solution was studied using gravimetric analysis. Different concentrations of the ZnO were varied for their anticorrosion behavior study on the metal. Results showed that the zinc oxide exhibited very good performance, with inhibition efficiency of up to 89%, at reducing the corrosion of aluminum in the acidic chloride environment.
... The E-pH diagram demonstrates that corrosion takes place in both alkaline and acidic environments. The protective layer is formed at pH 4-9 [71]. The diagram also shows that the equilibrium electrode potential between [Al(OH)4] -and Al, shifts to less noble values with increasing pH. ...
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Complex metallic alloys (CMAs) are materials composed of structurally complex intermetallic phases (SCIPs). The SCIPs consist of large unit cells containing hundreds or even thousands of atoms. Well-defined atomic clusters are found in their structure, typically of icosahedral point group symmetry. In SCIPs, a long-range order is observed. Aluminum-based CMAs contain approximately 70 at.% Al. In this paper, the corrosion behavior of bulk Al-based CMAs is reviewed. The Al–TM alloys (TM = transition metal) have been sorted according to their chemical composition. The alloys tend to passivate because of high Al concentration. The Al–Cr alloys, for example, can form protective passive layers of considerable thickness in different electrolytes. In halide-containing solutions, however, the alloys are prone to pitting corrosion. The electrochemical activity of aluminum-transition metal SCIPs is primarily determined by electrode potential of the alloying element(s). Galvanic microcells form between different SCIPs which may further accelerate the localized corrosion attack. The electrochemical nobility of individual SCIPs increases with increasing concentration of noble elements. The SCIPs with electrochemically active elements tend to dissolve in contact with nobler particles. The SCIPs with noble metals are prone to selective de-alloying (de–aluminification) and their electrochemical activity may change over time as a result of de-alloying. The metal composition of the SCIPs has a primary influence on their corrosion properties. The structural complexity is secondary and becomes important when phases with similar chemical composition, but different crystal structure, come into close physical contact.
... The main corrosion form of this alloy system in seawater and NaCl solutions is pitting [6,7]. The AlMg-Zn alloy is characterized by a very heterogeneous microstructure, consisting of an aluminum solid solution matrix and various intermetallic phases; their mechanical properties are due to the presence of these particles [8]. The outstanding importance of the microstructure and the influence of the intermetallic particles on the corrosion behavior were extensively discussed by Campestrini et al. [9] and Vander Kloet [10]. ...
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Light aluminum alloys have a great importance in industry owing to generally accessible costs, low density, good machinability, and corrosion resistance under certain environments. The present work studies aging treatments that preform important roles on the distribution and microstructural changes of two AlMg-Zn alloys, and the resulting effect on the corrosion behavior. The experimental AlMg-Zn alloys were cast and then heat treated at 200 °C, after the solubilization treatments were made, using different treatment times. These alloys showed important changes in their corrosion mechanisms, but mainly, corrosion started at AlxMgyZnz complex phases in both alloys. The optimal corrosion rates were reached after 5 and 24 hours of heat treatment. These results were obtained through electrochemical techniques in NaCl solutions, and by metallographic analysis using SEM and optical microscopy.
... Herein, based on the corrosion products observation and analysis by the authors of this paper, and references from the literature [69,70], the copper corrosion model and chemical equations for an electrical contact after MFG corrosion test have been discussed from Eqs. 1-14. Formation of Cu 2 O: ...
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Single-layer barrier systems such as Ni/Au and Ni–P/Au (the function of the ultra-thin Au top layer is not considered as a barrier), as opposed to bilayer stacks like Ni/Ni–P/Au, have been reported to display enhanced corrosion resistance. Within the single-layer barrier systems, Ni/Au appeared more corrosion resistant to neutral salt spray (NSS) test, while Ni–P/Au appeared more corrosion resistant to acidic mixed flowing gas (MFG) test. To explain such disparity factors potentially influencing corrosion resistance, such as internal stress, surface wettability and sulfur co-deposition have been examined. Interestingly, none of these factors could account for the disparity in the corrosion performance. Moving from a perspective of overall corrosion to one that focuses on the location of corrosion products was imperative to explain the disparity in corrosion resistance. Detailed pits analysis revealed that the disparity was caused by the edge porosity and corrosion product migration. These new concepts were further supported by a purposely designed experiment. Corrosion product analysis was also performed to explore the corrosion mechanisms in the NSS and MFG tests. The findings bring new insights into the design of corrosion-resistant metallic coatings in the future.
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In this paper, the development and the formation of the mild steel immersed in seawater that covered with enamel coating are investigated. The wire beam electrode (WBE) was applied to evaluate pitting corrosion and local inhomogeneous corrosion that happened on the coated surface of metal substrate. This method can obtain Maps that can show corrosion potential and galvanic current distributions and the specific values can be calculated from the WBE surface that was covered by enamel coating. Corrosion potential-current and electrochemical noise were successfully measured by using a WBE scanner and electrochemical workstation. This new linkage-test method means that the combined WBE-Rn has ability to characterize and analysis the process of enamel coating failing more accurately [Ref. 1; Ref. 2; Ref. 3; Ref. 4]. To some extent, the method can also predict the tendency and location of corrosion occurring. It was found that the coating has a good protective effect on the surface of the metal substrate because the corrosion potential is very positive and the corrosion current is very small. At the same time, in the course of the test, the distribution of the anode current is heterogeneous, as time increases, the original single anode current region gradually expands and is connected with the other anode regions in the final. In addition, corrosion often occurs at the boundary of the electrode (WBE) and then to the central area.
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Corrosion fatigue tests were performed on samples of a high purity Al-Zn-Mg alloy in humid nitrogen gas after pre-exposure to either vacuum or humid air. The results of these tests were compared to the results of fatigue tests performed in dry nitrogen, used as an inert reference environment, after the same pre-exposure treatments. The pre-exposure times were calculated by assuming that bulk diffusion of hydrogen was the rate limiting process in either hydrogen adsorption or desorption. Water vapor in the testing environment resulted in reduced fatigue lives; however, pre-exposure to humid air was just as detrimental as water vapor in the test environment. The pre-exposure embrittlement effect of humid air was found to be completely reversible when the samples were stored in a vacuum long enough to remove hydrogen, assuming a bulk diffusion coefficient of 1 x 10-13 m2/sec. These results confirm the hypothesis that the reduced fatigue lives of Al-Zn-Mg alloys in water vapor is due to hydrogen embrittlement.
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A recently developed technique for the artificial production of an Al2O3 film on ultrahigh-purity polycrystalline Al samples was employed. Electrochemical impedance spectroscopy (EIS), Auger electron spectroscopy (AES), and grazing angle X-ray diffraction (GAXRD) were used to investigate the artificial oxide film. The growth of aluminum oxide in water vapor (5 × 10-7 Torr) enhanced by 100 eV electron bombardment resulted in an artificial oxide film which exhibited a 10−30-fold improvement in electrical resistance in 3.5% NaCl solution compared to oxide films of the same thickness grown at 300 K in the absence of electron bombardment (thermal excitation only). These measurements suggest that the artificial aluminum oxide film may provide superior corrosion passivation qualities compared to thermally grown oxide films. The amorphous nature of the artificial oxide film was confirmed by GAXRD.