Synergistic inhibition and assessment of Y2O3 corrosion impact on AZ92 magnesium alloy by stir casting process in chloride media by response surface methodology

Abstract

This study explores the corrosion behavior of cast AZ92 magnesium alloy modified with 0–3.0 wt% Y₂O₃ produced by a stir casting process in 3.5% NaCl solution, both with and without inhibitors 0.01 mg/L AgNO₃, 0.01 mg/L Ce(NO₃)₃, and 0.01 mg/L Mo(NO₃)₂. A novel approach combining gravimetric analysis, electrochemical techniques (EIS, polarization), and response surface methodology (RSM) was used to optimize corrosion resistance (CRST). Results reveal that 2.5 wt% Y₂O₃ provides the lowest corrosion rate (0.80 mm/y) when Ce(NO₃)₃ present, which is attributed to refinement of β-phase. SEM confirmed compact Mg(OH)₂-rich surface films, while RSM identified Y₂O₃ content as the most influential factor (F = 531.18, p = 0.000), followed by time and media. Electrochemical tests showed enhanced polarization resistance (up to 1901.7 Ω) and stable passive films at 1.5–2.5 wt% Y₂O₃. However, higher Y₂O₃ levels reduced protection due to film instability and agglomeration. The synergistic role of Y₂O₃ and Ce(NO₃)₃ was most effective, with optimal conditions predicted by RSM. These findings provide a promising corrosion control strategy using rare earth oxides and multivariate optimization.