pH-Driven mechanistic transitions in pitting corrosion of selective laser melted AlSi10Mg in chloride Media

Abstract

This study investigates pH-driven mechanistic transitions in the pitting corrosion of selective laser melted (SLMed) AlSi10Mg alloy in 3.5 wt.% NaCl solution at pH 2, 6, and 12. The alloy was produced by laser powder bed fusion and examined using SEM/EDS and XRD before and after electrochemical exposure. Corrosion performance was evaluated using OCP, PDP, CPP, EIS, and CA. The electrochemical response followed the order pH 6 > pH 2 > pH 12. At pH 6, the alloy showed the most noble E corr (−754.4 mV), the lowest i corr (5.97 µA cm −2 ), and the lowest corrosion rate (0.065 mm year −1 ), indicating the highest passive-film stability. Acidic chloride solution (pH 2) increased i corr to 27.78 µA cm −2 and the corrosion rate to 0.303 mm year −1 because of chloride-assisted oxide dissolution and metastable pit activity. In contrast, alkaline exposure (pH 12) produced the most active E corr (−1062 mV), i corr of 7.45 µA cm −2 , and severe surface activation due to hydroxide-driven amphoteric dissolution through soluble aluminate formation. CPP analysis further confirmed pH-dependent pit stability, with narrower hysteresis at pH 6 and delayed repassivation under alkaline conditions. EIS showed the highest interfacial resistance at pH 6 and the weakest passive-film protection at pH 12.