Pyrrole-based silane primer for corrosion protection of commercial Al alloys: Part I: Synthesis and spectroscopic characterization

Chromate-free, direct-to-metal treatment using a pyrrole-based silane (PySi) was developed for protection against corrosion of as-received commercial wrought Al alloys of the series 1xxx, 2xxx, 5xxx and 6xxx. The metal surface was modified following the simple procedure for silane deposition by immersion in PySi hydrolyzed solution and curing. The spectroscopic characterization indicates that crosslinked composite PPySi network, containing both polysiloxane and polypyrrole units due to co-polymerization of PySi molecules, is produced by self-assembling of PySi soluble macro-oligomers onto the metallic substrates upon adsorption, with three-dimensional crosslink during heat treatment. Highly ordered well-packed and adherent PPySi film of the order of microns is obtained by just one immersion step in PySi primer. Control coatings of polymethylsiloxane (PMeSi) and polypyrrole (Ppy), the latter synthesized electrochemically, were investigated in parallel.