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Investigation of the initial stage of crevice corrosion on Al99.5 by electrochemical noise analysis

Untersuchung des Anfangstadiums der Spaltkorrosion von Al99.5 durch elektrochemische Rauschanalysen
: Schneider, M.; Galle, K.


Materials and corrosion 58 (2007), No.12, pp.983-991
ISSN: 0947-5117
Journal Article
Fraunhofer IKTS ()
Fraunhofer IFAM ()
Korrosionsprüfung; Rauschmessung; Aluminium; Aluminiumlegierung; Spaltkorrosion; Lochkorrosion; Anfangswert; Korrosionsinhibitor; Chromat; Korrosionsmechanismus; Intermetallische Phase; potentiostatische Prüfung; numerisches Verfahren

The electrochemical noise analysis (ENA) is a powerful tool to investigate the initial state of local corrosion processes as pitting corrosion or crevice corrosion on aluminium alloys. The focus of this work lays on Al99.5 (AA1050). The electrochemical measurements were carried out in solutions of 0.01 mol/1 Na2SO4 + 0.01 mol/1 NaCl and 0.01 mol/1 Na2SO4 + 0.1 mol/1 NaCl. In spite of the good corrosion protection and the very low passive current density the noise activity in the early state of corrosion can be very well observed. ENA was performed by using current noise measurement under potentiostatic control. The effect of chromate inhibitors on the noise activity of the initial state of corrosion on Al99.5 is surprisingly negligible. This phenomenon is discussed in the paper. The intermetallics are preferred sites for the initiation of corrosion processes. The microstructure investigation has shown that technically pure aluminium has a small content of iron rich intermetallics (Al3Fe). The microstructure of the aluminium alloys (e.g. AA2024 and AA6013) is characterised by a number of intermetallic phases (e.g. Al2Cu, Al2CuMg, Mg2Si). Because of the small content of additional elements in Al99.5 the influence of intermetallics should be negligible. Therefore, the corrosion behaviour of Al99.5 can be considered as a reference for medium and high-strength aluminium alloys. On that score, it is very important to know the liability of Al99.5 against crevice corrosion.
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