The local electrochemical measurement and corrosion mechanism of the multi-layer aluminium sheets (AA4343/AA3xxx/AA4343 and AA7072/AA3xxx/AA4343) after brazing are determined by a combination of mechanical polishing and work function calculation based on density functional theory. The work functions of (100), (110), and (111) crystal planes of Si and α-Al(Fe,Mn)Si particles which are common in multi-layer aluminium sheets are calculated. The results demonstrate Si and α-Al(Fe,Mn)Si particles are considered to be cathodic with respect to the Al matrix, thus promoting cathodic reactions. The potential differences between the Si and α-Al(Fe,Mn)Si particles with respect to the Al matrix may lead to localized dissolution of the Al matrix. Besides, the microstructure and composition of multi-layered aluminium sheets are studied by optical microscopy, scanning electron microscopy, and glow discharge optical emission spectrometry and compared with those obtained for conventional multi-layer aluminium sheets (AA4343/AA3xxx/AA4343). The presence of the AA7072 layer reduces the outward diffusion of copper. In addition, the AA7072 sacrificial layer exhibits a large potential difference against the core material for a long time, thereby improving corrosion protection.

中文翻译：

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用于汽车热交换器的渐变多层铝板

钎焊后多层铝板（AA4343/AA3xxx/AA4343和AA7072/AA3xxx/AA4343）的局部电化学测量和腐蚀机理是通过机械抛光和基于密度泛函理论的功函数计算相结合来确定的。计算了多层铝板中常见的Si和α-Al(Fe,Mn)Si颗粒的(100)、(110)和(111)晶面的功函数。结果表明，Si 和 α-Al(Fe,Mn)Si 颗粒被认为是相对于 Al 基体的阴极，从而促进了阴极反应。Si 和 α-Al(Fe,Mn)Si 颗粒相对于 Al 基体的电位差可能导致 Al 基体的局部溶解。此外，通过光学显微镜研究了多层铝板的微观结构和成分，扫描电子显微镜和辉光放电光学发射光谱法，并与传统多层铝板 (AA4343/AA3xxx/AA4343) 获得的结果进行比较。AA7072 层的存在减少了铜的向外扩散。此外，AA7072牺牲层对芯材长期呈现较大的电位差，从而提高防腐蚀能力。