Electrochemical characterisation of the porosity and corrosion resistance of electrochemically deposited metal coatings

This study focuses on the electrochemical techniques used to assess the porosity and corrosion resistance of various electrodeposited metal coatings. The objective was to illustrate the determination of porosity and, subsequently, the corrosion resistance through electrochemical data gathered from three coating/substrate systems: electroless nickel on aluminium and steel, as well as immersed gold coatings on electroless copper-plated ABS polymer. The experiment employed Tafel extrapolation and linear polarisation resistance methods to ascertain the corrosion rates of the coated substrates, where nickel coatings were found to be as thick as 24 µm, and gold deposits ranged between 75 and 190 nm. Various testing environments were utilized, including a 5% w/v NaCl solution for aluminium samples and specific acid solutions for steel and ABS samples. The research revealed significant insights into the relationship between coating porosity and corrosion performance, indicating that through-porosity is a critical factor affecting the lifespan and quality of coated components. It was determined that galvanic cells formed in the coatings under acidic conditions promote corrosion, underlining the importance of assessing porosity for enhanced material durability.