Atmospheric corrosion aluminum

S.C. Byrne and A.C. Miller, Effect of Atmospheric Pdlutant Gases on the Formation of Coirosive Condensate on Aluminum, Atmospheric Corrosion of Metals, S.W. Dean, Jr. and EC. Rhea, Ed., STP 767, ASTM, 1982, p 395... 

Aluminum Paints. Mica is substituted for up to 25% of the aluminum in this type of paint (qv) as an economic measure. Mica is inert which tends to protect the more reactive aluminum from corrosive atmospheres, thus helping the paint to maintain its luster. 

Atmospheric corrosion is electrochemical ia nature and depends on the flow of current between anodic and cathodic areas. The resulting attack is generally localized to particular features of the metallurgical stmcture. Features that contribute to differences ia potential iaclude the iatermetaUic particles and the electrode potentials of the matrix. The electrode potentials of some soHd solutions and iatermetaUic particles are shown ia Table 26. Iron and sUicon impurities ia commercially pure aluminum form iatermetaUic coastitueat particles that are cathodic to alumiaum. Because the oxide film over these coastitueats may be weak, they can promote electrochemical attack of the surrounding aluminum matrix. The superior resistance to corrosion of high purity aluminum is attributed to the small number of these constituents. 

Zinc diffusion is used for protection against atmospheric corrosion. Aluminum diffusion is used to improve the oxidation resistance of low-carbon steels. 

BS2569 Sprayed Metal Coatings. Part 1 Protection of Iron and Steel by Aluminum and Zinc Against Atmospheric Corrosion. ... 

The few reported cases concerning other metals, like zinc, aluminum, and magnesium, attest their susceptibility to corrosion due to volatile compounds in the museum environment [271]. Iron is naturally vulnerable to atmospheric corrosion whatever the pollutants, and the conservation of ferrous artifacts implicates a precise control of relative humidity, often requiring a surface protection like varnish, wax, or oil [272]. 

Atmospheric Corrosion. The aluminum-based alloys in general are corrosion resistant to outdoor exposure with the exception of copper-bearing alloys. The Alclad alloys gave the best performance. The loss in tensile strength has been used as a measure of corrosivity and the loss of 1-2% of tensile strength over a period of 1 yr and in particular a loss of 17% was observed with 2017T alloy in 1 yr of outdoor exposure. 

Although the degree of atmospheric corrosion of copper and its alloys depends upon the corrosive agents present, the corrosion rate has been found to generally decrease with time. The copper and its alloys such as silicon bronze, tin bronze usually corrode at moderate rates, while brass, aluminum bronze, nickel silver, and copper-nickel corrode at a slower rate.51 The most commonly used copper alloys are Cl 1000, C22000, C38500 and C75200. 

Materials such as metals, alloys, steels and plastics form the theme of the fourth chapter. The behavior and use of cast irons, low alloy carbon steels and their application in atmospheric corrosion, fresh waters, seawater and soils are presented. This is followed by a discussion of stainless steels, martensitic steels and duplex steels and their behavior in various media. Aluminum and its alloys and their corrosion behavior in acids, fresh water, seawater, outdoor atmospheres and soils, copper and its alloys and their corrosion resistance in various media, nickel and its alloys and their corrosion behavior in various industrial environments, titanium and its alloys and their performance in various chemical environments, cobalt alloys and their applications, corrosion behavior of lead and its alloys, magnesium and its alloys together with their corrosion behavior, zinc and its alloys, along with their corrosion behavior, zirconium, its alloys and their corrosion behavior, tin and tin plate with their applications in atmospheric corrosion are discussed. The final part of the chapter concerns refractories and ceramics and polymeric materials and their application in various corrosive media. 

For aluminum the corrosion rate especially in polluted atmosphere is usually lower at open outdoor compared to sheltered exposure. This indicates that the composition of the surface layer of moisture which in sheltered positions is created by dry deposition of pollutants, is more corrosive than precipitaiton. 

Chromium and aluminum are resistant to atmospheric corrosion individually but when porous chromium in intimate contact with aluminum is exposed to high humidities substantial corrosion occurs at the interface of the two materials. This is illustrated by the roughening data of Figure 4. Auger electron spectroscopy shows 0, S,... 

The corrosion resistance of anodized aluminum is more or less comparable with the untreated aluminum in an acidic and alkaline environment. The formation of pits is decreased under atmospheric corrosion conditions ( pitting corrosion). 

ISO CORRAG [23], the International Organization for Standardization (ISO) has implemented a classification system for evaluating atmospheric corrosivity and on the basis of variables that are fairly easy to obtain [24, 25]. This ISO classification has found several applications, for example, to predict the long-term corrosion behavior in different environments and to evaluate the effect of protective coatings. It contains two principally different approaches of assessing the corrosivity of any outdoor atmospheric environment. The first is based on exposure of standard specimens of steel, copper, zinc, and aluminum for one year whereby the corrosion effect is measured through mass loss measurements. One of five measured corrosivity classes... 

The shiny appearance, low-weight per volume, favorable mechanical properties such as material strength, ease of forming, and handling are some favorable features of aluminum and hence its use in the food industry. In addition, aluminum has a better corrosion resistance than carbon steel as it readily forms a protective film that prevents further atmospheric corrosion. Aluminum is also lighter than stainless steel and hence its use in beverage cans. 

Gonzalez et al. [43] and Lopez et al. [44] investigated the atmospheric corrosion of aluminum with different layers of anodic films in eleven different environments with estimated levels of salinity. Electrochemical corrosion techniques and electrochemical impedance spectroscopy were used to estimate the corrosion rates. The results indicated that at critical levels of anodic film thicknesses, the aluminum could be protected for a long time even when exposed to high levels of salinity. 

J.A. Gonzales, M. MorciUo, E. Escudero, E. Otero, Atmospheric corrosion of bare and anodized aluminum in a rvide range of environmental conditions. Part 1 visual observation and gravimetric results. Surf. Coat. Tech. 153 (2002) 225-234. 

Lead by itself is not particularly harmful. However, in conjunction with any concentration of aluminum, it appears to accelerate corrosion. Copper improves atmospheric corrosion resistance and retards intergranular attack. This effect may not make any great difference with longterm corrosion. Magnesium improves the corrosion resistance of zinc and can counteract any bad effects of aluminum. 

Fig. 2.48 Thirteen-year exposures of Galvalume in marine and industrial atmospheres. Corrosion performance of galvanized, aluminum-coated, and Galvalume sheet in (a) a marine atmosphere (Kure Beach, NC 250 m lot), (b) a severe marine atmosphere (Kure Beach, NC 25 m lot), and (c) an industrial atmosphere (Bethlehem, PA) (Allegra et al., 1985).

Zinc-4% aluminum alloy castings produced according to recognized specifications behave much like pure zinc. They are resistant to atmospheric corrosion, and usually more zinc can be lost without affecting performance than is the case with zinc coatings. 

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