Phosphating modification of agricultural carbon steel surface with metal ions and nanotechnology-based enhancement for improved anticorrosion properties

Abstract

Enhancing the corrosion protection of carbon steel is essential for extending the service life of components used in aggressive environments. In this work, zinc phosphate coatings are developed on galvanized carbon steel using phosphating baths modified with Cr²⁺, Cu²⁺, and Al²⁺ ions, followed by sealing in a sodium molybdate solution. The influence of these metal-ion additives on the structural, morphological, mechanical, and electrochemical properties of the resulting coatings is systematically evaluated. X-ray diffraction analysis revealed the formation of zinc phosphate phases with distinct crystallographic characteristics depending on the type of additive, indicating that metal ions strongly influence crystal nucleation and growth. Atomic force microscopy showed notable differences in surface topography, with copper-activated coatings exhibiting the lowest surface roughness and the most homogeneous morphology. Adhesion strength measurements demonstrated that phosphate and sealed coatings significantly outperformed conventional hot-dip galvanized steel, with copper-containing phosphate layers achieving the highest interfacial bonding strength. Electrochemical polarization studies confirmed a substantial improvement in corrosion resistance for all modified coatings compared to additive-free phosphating. The copper-modified phosphate coating provided the most effective barrier against corrosive attack. Furthermore, environmental exposure tests showed excellent coating stability without cracking or delamination. In addition, the incorporation of nanotechnology offers a promising pathway to further enhance coating performance. The use of nanoparticles and nanoscale surface modifications can improve coating density, reduce porosity, and increase resistance to corrosive environments by enhancing barrier properties and interfacial bonding at the nanoscale.