A PPy modified Al₂O₃-mullite coating on Al alloys for anti-static electricity and corrosion resistance

Accumulated charges seriously interfere with the performance of precision instruments and may induce tremendous accidents. In order to endow 2A12-T4 Al alloys with corrosion resistance and anti-static electricity simultaneously, a polypyrrole (PPy) layer is fabricated on micro-arc oxidized Al₂O₃-mullite coating by chemical oxidation polymerization (COP). With the prolonged COP treatment, PPy nanoparticles gradually grow and combine together on surface of Al₂O₃-mullite coating, and a dense and uniform PPy layer is formed after the COP treatment of 1.5 h, which dramatically decreases resistivity and sheet resistance of the composite coating to 0.28 kΩ cm and 3.86 KΩ/□, respectively. However, the excessively prolonged COP treatment induces repaid growth of PPy particles, resulting in the formation of large gaps in the PPy layer, which obviously decrease conductivity of the composite coating. Meanwhile, the PPy layer formed at 1.5 h of COP treatment protects the surface from serious salt spray erosion due to the increased hydrophobicity and blocking and deoxidizing function, and it also gives the composite coating good anti-static stability in acidic solution with pH = 3. This work provides a promising strategy for Al alloys which service in corrosive and electrostatically accumulated environment.