Preparation and characterization of electrically conductive nano-ZnO-doped Ti/Zr composite conversion coating on aluminum alloy

The integration of semiconductive nano-ZnO into a Ti/Zr-based solution has facilitated the development of a conductive coating on aluminum alloy surfaces. A comprehensive characterization of the coating's morphology, microstructure, electrical conductivity, and corrosion resistance was conducted utilizing a suite of analytical techniques, including SEM, FIB-SEM, EDS, XPS, UV-vis, FTIR, and an electrochemical workstation. Significantly, the electrical contact resistance (ECR) of the coating experienced a substantial decrease when subjected to a pressure of 200 psi, plummeting from 0.1907 Ω in⁻² in the absence of nano-ZnO to 0.0621 Ω in⁻² with the inclusion of nano-ZnO. Concurrently, the band gap of the coating was observed to diminish from 3.189 eV without nano-ZnO to 2.708 eV with nano-ZnO, indicating improved semiconductor properties. The coating exhibited a three-layer structure consisting of a substrate-close layer of nano-ZnO, a middle layer composed of Na₃AlF₆ crystals, and an outermost layer comprising ZnO and metal–organic complexes. The incorporation of nano-ZnO induced a striking morphological transition from a pebble-like to a cubic structure, along with a notable change in the coating's color. These findings collectively demonstrate the transformative impact of nano-ZnO on the multifaceted attributes of the conversion coating, endowing it with superior electrical characteristics.