Gallic acid grafted chitosan inhibits Al alloy corrosion and temperature optimized ultrasound removes scale/rust: A clean and protect combined strategy

In the cooling system of high-voltage direct current converter valves, aluminum alloy C3003 heat sinks suffer from severe electrochemical corrosion and scaling deposition, threatening equipment safety. This study develops a combined strategy of a green corrosion inhibitor and ultrasonic cleaning. Gallic acid-grafted chitosan (CG) was synthesized via the carbodiimide method, and Fourier transform infrared spectroscopy confirmed successful grafting. Electrochemical tests in 3.5 wt. % NaCl solution show that 200 ppm CG increases charge transfer resistance from 0.958 × 104 to 5.626 × 104 Ω cm2 with an inhibition efficiency of 83.0%, effectively suppressing chloride-induced pitting. For pre-scaled C3003, ultrasonic cleaning was evaluated by weight loss and 3D optical profilometry. Under 40 kHz, 240 W, and 10 min, the cleaning rate increases with temperature (198 g m−2 h−1 at 45 °C and 338 g m−2 h−1 at 75 °C), but surface roughness improves best at 60 °C (26.9% reduction), while excessive temperature damages the surface. In conclusion, CG inhibits corrosion and optimized ultrasonic cleaning removes scale, providing a feasible technical pathway for safe operation of aluminum alloy C3003 in converter valve cooling systems.