Structure–property correlation of Atmospheric DBD plasma-treated Al6061-T6 for enhanced wettability and coating adhesion

Atmospheric-pressure dielectric barrier discharge (DBD) air plasma treatment was investigated for surface activation and coating adhesion improvement of AA6061-T6 aluminum alloy. Alloy coupons were treated in ambient air using a 12 kV, 0.7 mA-rated AC power supply with a 5 mm discharge gap for 2, 4, 6, and 8 min. Plasma treatment reduced the water contact angle from 68° for the untreated, weakly hydrophilic alloy to approximately 35° after 4 min. Surface free energy increased with treatment duration, while paint detachment in the cross-hatch adhesion test decreased from 72% for the untreated alloy to 3% after 8 min of treatment, despite the stabilization of wettability after 4 min. X-ray photoelectron spectroscopy (XPS) indicated changes in carbon- and oxygen-containing surface species, including Al–O and Al–OH groups. Atomic force microscopy (AFM) showed a reduction in average surface roughness (Sa) from 52.3 nm to 17.8 nm after 8 min. The changes in surface chemistry and morphology were associated with improved coating adhesion. Aging measurements showed rapid recovery of the plasma-induced wettability, with the water contact angle increasing from 35° immediately after treatment to 47.5°, 63°, 67°, and 68° after 0.5, 1, 2, and 3 h, respectively, while paint detachment increased from 3% immediately after treatment to 65% after 2 h. Atmospheric-pressure DBD plasma treatment provides a dry surface activation method for AA6061-T6 aluminum alloy. However, the observed recovery of wettability indicates that coating should preferably be applied soon after plasma treatment.