Photothermal Response and Multi-Factor Durability of Glass-Assisted Laser-Blackened Superhydrophobic Al-Mg Surfaces

Nanosecond laser processing of an Al-Mg alloy in direct contact with soda–lime glass was used to produce black surfaces, subsequently rendered superhydrophobic by O2 plasma activation and vapor-phase fluorosilane functionalization. Processing under glass changed the hierarchical morphology while producing roughness parameters comparable to those obtained without glass. Elemental analysis revealed incorporation of glass-derived Si, Na, and Ca, while X-ray diffraction identified nanocrystalline elemental Si with coherent domain sizes of approximately 10 nm. These observations are consistent with aluminothermic reduction of glass-derived silica during laser processing. Under the tested illumination conditions, the black surface exhibited a temperature rise of 28.3 °C, approximately 32% greater than the pristine alloy and 9% greater than the surface laser-textured without glass. A 15 min O2 plasma treatment provided the highest water-immersion stability among the conditions investigated. After 90 h in water, the optimized surface retained a contact angle of 166.1° and a roll-off angle of 4.6°. After prolonged exposure of the coating to abrasive wear under conditions of oscillating sand movement and impact loads during the falling-sand test, the contact angles remained significantly above 150°. Both oscillating-sand and falling-sand abrasion impaired droplet mobility more strongly than apparent contact angle. Glass-assisted processing thus provides a route to black, Si-containing superhydrophobic Al-Mg surfaces, while the durability results identify droplet mobility as a more sensitive indicator of mechanical degradation than static contact angle.