Effect of acid pickling treatment of stainless steel substrate on adhesion strength of electrodeposited copper coatings using non-cyanide electrolyte

In recent years, copper-based antimicrobial coatings have gained popularity in healthcare and public recreation facilities. The morphology, topography, and adhesion strength are decisive properties for copper coatings to have long-term antimicrobial effectiveness in hospital environments. This work explores the effect of multistage acid pickling treatment of AISI 304 stainless steel substrate on the adhesion strength of the copper coating. The copper coating was obtained by electrodeposition using an alkaline non-cyanide electrolyte. After the fourth stage of acid pickling, the copper coating had an excellent adhesion strength, up to 9 MPa. Glow discharge optical emission spectroscopy (GDOES) examination revealed no oxide scales or other contaminants on the SS surface after the fourth (final) stage of acid pickling. Using a non-contact optical profilometer, it was observed that the roughness of the substrate increased with each stage of the pickling treatment. The surface topography analysis confirms the increased density of the interlocking sites, which favors the adhesion of the coating. On the other hand, the microstructure of the copper coating showed a cauliflower-like morphology with an average nodule size of 28 nm. Transmission electron microscopy confirmed that the coatings have nano-scaled crystallites with internal twins inside the grains of copper coatings.