Influence of Cavitation in Seawater on the Etching Attack of Manganese-Aluminum-Bronzes

During cavitation investigations with manganese-aluminum-bronzes (MAB) in seawater using ultrasound (US), it was found that the microstructure of the bronze was developed by etching. To investigate this phenomenon in more detail, metallographically polished MAB samples were US-treated in synthetic seawater. On the one hand, pulsed ultrasound was used with a sonotrode in order to be able to observe the effects of cavitation. On the other hand, an ultrasonic bath with less power than the sonotrode was used to investigate the influence of ultrasound on the electrochemical response of the MAB. It was found that the k-phase is attacked most severely by cavitation, followed by β-phase and the α-phase. Potentiostatic measurements indicated that the transport of oxygen to, and of metal ions from the metal surface is enhanced by the ultrasound, which then leads to increased corrosion rates.