Synergistic sealing of Ni-electroplated steel with an ATMP/Zn-BTA composite for enhanced corrosion protection

Nickel electroplating is a critical surface treatment technology that provides essential corrosion protection and ensures high electrical conductivity, both vital for maintaining the structural integrity and operational safety of modern metal components. However, inherent micropores within the plated layer can compromise its protective function and accelerate substrate corrosion. In this study, we present a novel, environmentally friendly, chromium-free sealing strategy based on an aminotrimethylene phosphonic acid (ATMP)-Zn²⁺ system, synergistically enhanced with benzotriazole (BTA). The specially formulated sealing bath selectively reacts with substrate exposed at pore bottoms while remaining inert to the sound nickel surface, allowing targeted pore filling through strong –PO(OH)₂–metal interactions. The resulting coating significantly reduces porosity (from 13.3 ± 1.6 cm⁻² to 1.7 ± 0.9 cm⁻²), maintains excellent electrical conductivity, and endures 2 h of neutral salt spray without corrosion. XPS and FTIR analyses confirm BTA’s synergistic role via N-H⁺···⁻O-P bonds and the optimized P-O-M coordination. This environmentally friendly approach offers a high-performance sealing solution that preserves the functional properties of Ni electroplating layers.