Abstract

Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and microstructure characterization were performed on directionally solidified samples of the Al–3Cu–2Si alloy in order to study their corrosion behavior in a 0.2 M HCl electrolyte. Corrosion resistance of the investigated samples was correlated with solidification parameters, such as growth (V_L), cooling rates (T_R) and secondary dendritic spacing (λ₂). Optical microscopy was used to characterize both the as-cast and corroded microstructures. For an immersion time of 24 hours in acidic solution, optical micrographs indicated that Si addition to Al-3Cu alloy promoted a significant decrease in the average fractions of α-Al phase increasing anodic activity of the Al-3Cu-2Si alloy. Using Tafel extrapolation, it is shown that the secondary dendritic arm spacing (λ₂) acts as a factor influencing the corrosion current density (Icorr). All the EIS diagrams reveal a unique capacitive time constant and the size of the semi-circle decreases with increasing the time of immersion. Nyquist plots demonstrate that higher λ₂ values cause a decrease in resistance of polarization, indicating the presence of a very thin film of aluminum oxide associated with a lower corrosion resistance.

Graphic Abstract

中文翻译：

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水平凝固 AlCuSi 合金试样的电化学腐蚀研究

摘要

对 Al-3Cu-2Si 合金的定向凝固样品进行动电位极化、电化学阻抗谱 (EIS) 和微观结构表征，以研究它们在 0.2 M HCl 电解质中的腐蚀行为。所研究样品的耐腐蚀性与凝固参数相关，例如生长 (V _L )、冷却速率 (T _R ) 和二次枝晶间距 (λ ₂）。光学显微镜用于表征铸态和腐蚀的微观结构。在酸性溶液中浸泡 24 小时后，光学显微照片表明，添加到 Al-3Cu 合金中的 Si 促进了 α-Al 相平均分数的显着降低，从而提高了 Al-3Cu-2Si 合金的阳极活性。使用 Tafel 外推法，表明二次枝晶臂间距 (λ ₂ ) 是影响腐蚀电流密度 (Icorr) 的一个因素。所有 EIS 图都显示了一个独特的电容时间常数，半圆的大小随着浸入时间的增加而减小。奈奎斯特图表明更高的 λ ₂ 值导致极化电阻降低，表明存在与较低耐腐蚀性相关的非常薄的氧化铝膜。

图形摘要