Experimental approach and assessment of Zr conversion coatings on Al alloy using response surface methodology

This study extended the use of response surface methodology (RSM) to explore the experimental space, identify optimal conditions for deposition and drying, and assess factor interactions for zirconium conversion coatings on aluminium alloy 5754. Corrosion resistance in a dilute Harrison's solution was evaluated using a non-electrochemical drop test and electrochemical techniques. Surface analysis supported the electrochemical findings obtained with the chosen RSM conditions. Unlike zinc and cold-rolled steel, AA5754 exhibits heightened sensitivity to the interplay of pH, conversion time, and H 2 ZrF 6 concentration, which is attributed to the presence of intermetallic particles governing cathodic reactions and the subsequent conversion processes. • RSM assessed ZrCC best-performing conditions and best-feasible evaluation techniques. • Drop test suitable for quick AA5574-ZrCCs assessment at pH ≥ 4 after 24 h air-drying. • R p is more convenient than j corr for evaluating AA5574-ZrCCs. • The full coverage of ZrCC at conversion time ≥ 230 s. • EIS predicts prolonged corrosion protection based on more even ZrCC thickness at lower concentrations.