Aluminium alloys exfoliation

Test method for exfoliation corrosion susceptibility in 2XXX and 7XXX series aluminium alloys (EXCO test)... 

Method for visual assessment of exfoliation corrosion susceptibility of 5XXX series aluminium alloys (Asset test)... 

Several aluminium alloys show very good corrosion resistance in various atmospheres. Some pitting occurs, but the pits remain small. Maximum depth seldom exceeds 0.5 mm during 6-20 years of exposure it is usually in the order of 0.1 mm. Some alloys may, however, be attacked by intergranular corrosion or exfoliation corrosion (see Section 7.7). Extensive galvanic corrosion may occur on aluminium in contact with copper, mild steel (in marine atmosphere) and graphite, less in contact with stainless steel, while aluminium is compatible with zinc [8.2]. 

Aluminium alloys Surface pitting, intergranular and exfoliation White or grey powder... 

Historically, various investigators in Europe have used hydrochloric acid-px>tassium dichromate solutions for testing the exfoliation susceptibility of all types of aluminum alloys. An example is the Russian Stanchtid GOST 9.904-82, Aluminium Alloys Methods of Accelerated Exfohation Corrosion Testing [22]. It should be noted, however, that hexavalent chromium (Cr ) solutions are considered undesirable for health and environmental considerations and have been prohibited in some countries. 

Braun, R., Exfoliation Corrosion Testing of Aluminium Alloys, British Corrosion Journal, Vol. 30, No. 3, 1995, pp. 203-208. 

Corrosion of metals and alloys—Exfoliation corrosion testing of aluminium alloys Corrosion-resistant cast steels for general applications... 

All aluminium alloys undergo identical galvanic corrosion. In addition, intercrystaUine and exfoliation corrosion may occur in those alloys of the 2000, 5000, 6000 and 7000 series that are susceptible to these forms of corrosion. 

Testing corrosion of exfoliation corrosion of aluminium alloys Determination of susceptibility to exfoliation corrosion of alloys of the 2000 and 7000 series alloys (EXCO)... 

Hudson reported lives of about 4y years for 38 /tm thick metal-sprayed aluminium coatings on steel exposed at Sheffield, and more than 1 ly years for coatings 75/tm thick. Sprayed aluminium coatings (approximately 125/tm thick) have also provided complete protection against exfoliation and stress corrosion to aluminium-copper-magnesium (HE 15) and aluminium-zinc-magnesium (DTD 683) alloys in tests lasting up to 10 years in industrial and marine environments . 

Uniform corrosion is not observed because it is so minute that it cannot be measmed. Other forms of corrosion of aluminium and its alloys such as exfoliation corrosion, stress corrosion, etc. are of course possible on age-hardenable alloys of the 2000 and 7000 series when exposed to weathering. However, the selection of alloys and their protection, if present, normally prevents these forms of corrosion from occurring in outdoor applications such as buildings or bridge railings. 

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