Multifunctional Polymer Coatings with Enhanced Corrosion Resistance and Spot-Weldability for Mild Steel

Abstract

In this study, we synthesized conducting polyaniline in its emeraldine salt form (PANI ES) and subsequently used it for the in situ preparation of a spot weldable polyamic acid–PANI ES (PAA–PANI ES) composite. The composite was applied onto mild steel using an automatic bar coater, and upon drying, it converted into a uniform polyimide–PANI ES (PI–PANI ES) coating with a thickness of 10 ± 2 µm. The PI–PANI ES–coated substrates demonstrated excellent spot weldability, whereas substrates coated with pure PI were not weldable. The PI–PANI ES coating also provided markedly improved corrosion protection, achieving >500 h to reach 5% red rust in comparison to ~120 h for the pure PI coating. Both coating systems PI and PI–PANI ES exhibited strong adhesion to the mild steel substrate and successfully passed the required forming evaluations. In addition, both coatings adhered well to polyester-based powder paint. Incorporating conducting PANI ES powder into the PI matrix enhanced both the corrosion resistance and AC conductivity of the overall coating system.