Mechanism of Corrosion of Cast Aluminum-Silicon Alloys in Seawater. Part 2: Characterization and Field Testing of Sol-Gel-Coated Alloys in the Adriatic Sea

Abstract

Two hybrid sol-gel coatings, one acrylate-based and the other epoxy-based, were synthesized and deposited on two cast aluminum-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 characterized 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 for simulating vessels in motion or gentle cleaning. Although biofouling was formed during immersion, as analyzed 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.