Influence of microstructural characteristics on the corrosion response of Al–Sn–Zn alloys in dilute NaCl solution

This study investigates the corrosion characteristics of three Al–Sn–Zn alloys (Al–20Sn–5Zn, Al–20Sn–10Zn, and Al–10Sn–10Zn, all wt%) in a 0.06 M NaCl solution, with focus on the effects of the microstructural length scale. Each alloy was fabricated under a wide range of solidification cooling rates. Then, for each alloy, samples with primary dendrite arm spacings (λ1) of approximately 32 and 80 μm were examined to assess the role of two different microstructural length scales on corrosion performance. The results show that the three alloys exhibit similar corrosion behaviors, but the Al–10Sn–10Zn alloy with coarser microstructure shows a slight tendency to exhibit the lowest corrosion current density (iCOR). This slight improvement in the corrosion behavior is mainly attributed to the synergistic effects of a higher Zn-rich phase fraction, which acts as a sacrificial anode, and lower fraction of Sn, which contributes to reduce the susceptibility to localized corrosion. For a given alloy, the variation in λ1 had a negligible effect on the corrosion behavior. Electrochemical impedance spectroscopy measurements revealed similar polarization resistance values across the studied alloys, while potentiodynamic polarization curves exhibited a sharp increase in anodic current density, indicating active corrosion without passivation for the three alloys. Microstructural characterization confirmed the presence of Sn-rich particles, nobler phases that promote corrosion at the interface with Zn-rich particles and the Zn-supersaturated α-Al matrix. This study contributes to understanding the role of alloy composition and microstructure in improving the corrosion resistance of Al–Sn–Zn alloys, making them promising candidates for applications in surface engineering.