Covalent surface modification of 2024 aluminum alloy surface by self-assembly dodecyl phosphate film towards corrosion protection

This work was to prepare a layer of dodecyl phosphate (DDPO4) film on 2024 aluminum alloy substrate for corrosion protection by self-assembling. The prepared DDPO4 self-assembly monolayers (SAMs) properties were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle measurement (CA), and electrochemical impedance spectroscopy (EIS). Experimental results indicated that DDPO4 was successfully assembled on aluminum alloy substrate via covalent bond attachment. The modified surface was hydrophobic due to the DDPO4 attached to the oxide surface and a hydrocarbon tail-up orientation. In order to build a molecular adsorption dynamics model, the impact of temperature and pH values for assembling process has also been evaluated. Accelerated corrosion test showed that the DDPO4 modified 2024 aluminum alloy substrate exhibited excellent corrosion resistance. The charge transfer resistance of the DDPO4 covered aluminum alloy was ∼100 times larger than that of the blank aluminum alloy. The molecular dynamic (MD) simulation for DDPO4 adsorbed on the Al₂O₃(110) face indicate that the head group of DDPO4 is the active group and bind as tridentate with the O in P=O bond can adsorbed on the Al₂O₃ surface.