Mechanism of corrosion of cast aluminium-silicon alloys in seawater.
 Part 2: Characterisation and field-testing of sol-gel coated alloys in the Adriatic Sea

Two hybrid sol-gel coatings, one acrylate-based and the other epoxy-based, were synthesised and deposited on two cast aluminium-silicon alloys, Al-Si9-Cu3 and Al-Si7-Mg0.3. Field immersion testing was performed in the Adriatic Sea and lasted 8 months. Coatings were characterised before and after immersion in terms of morphology, structure, composition and electrochemical properties in artificial seawater. The level of biofouling was documented, and sonication was used as a procedure simulating vessels in motion or gentle cleaning. Although biofouling was formed during immersion, as analysed by scanning electron microscopy, it was removed by sonication in a large proportion. X-ray photoelectron and glow-discharge optical emission spectroscopies confirmed that the coatings preserved their structure and that no significant dissolution occurred. Both coatings showed better barrier properties when deposited on Al-Si7-Mg0.3 alloy and also exhibited the highest ability of biofouling release, making them good candidates for further development.