Electrochemical characterization of plasma polymer coatings in corrosion protection of aluminum alloys.

摘要

Low-temperature plasma polymerization is a new and promising pretreatment technique to create environmentally friendly coating systems with good corrosion protection for aluminum (Al) alloys. The effects of plasma pretreatment and plasma polymerization on corrosion protection of alclad Al alloy 2024-T3 ([2A]) were characterized using electrochemical techniques, including cyclic polarization (CP) and electrochemical impedance spectroscopy (EIS). The [2A] panels were coated with an ultrathin layer (∼50 nm) of plasma polymers in a direct current (dc) glow discharge of trimethylsilane (TMS) or its mixtures with O2 or N2. The CP measurement results showed that the plasma polymer coated [2A] panels exhibited more negative corrosion potentials (Ecorr), smaller corrosion currents (I corr), and no surface passivation when compared with uncoated [2A] panels. The lower values of Icorr imply a higher corrosion resistance on the plasma polymer coated [2A]. When investigated using EIS, these plasma polymer coated [2A] panels exhibited higher impedance (|Z|) at low frequency when first immersed in electrolyte solution, yet degraded quickly to the similar level as uncoated controls within one day of immersion. These results illustrated that thin plasma polymer films provided a certain but very limited corrosion resistance to [2A] substrate; their dominant role in plasma interface engineered coating systems still lies mostly in their adhesion enhancement at metal/paint interface as observed in our previous studies and further confirmed in this study.