通过测定Al-Mg-Si合金晶界各组成相的极化曲线及不同Mg/Si比 Al-Mg-Si合金晶界组成相(Al-Mg2Si及Al-Mg2Si-Si)间的动态电化学偶合行为，研究了不同Mg/Si比Al-Mg-Si合金的晶间腐蚀机理。研究表明，晶界Si电位比其边缘Al基体正，在整个腐蚀过程中作为阴极导致其边缘Al基体的阳极溶解。晶界Mg2Si电位比其边缘Al基体负，在腐蚀初期将作为阳极而发生阳极溶解；由于Mg2Si中活性较高元素Mg的优先溶解，不活泼元素Si富集，致使Mg2Si电位正移，甚至与其边缘Al基体发生极性转换，导致其边缘Al基体的阳极溶解。Mg/Si>1.73的Al-Mg-Si合金晶界只存在不连续分布的含Mg、Si的析出相，不能在晶界形成连续腐蚀通道，合金不表现出晶间腐蚀敏感性。Mg/Si<1.73的Al-Mg-Si 合金晶界同时析出含Mg、Si析出相和Si粒子；腐蚀首先萌生于 Mg2Si相；而后，Si粒子一方面导致其边缘无沉淀带严重的阳极溶解，另一方面通过加速Mg2Si和晶界无沉淀带的极性转换，协同促进了Mg2Si边缘无沉淀带的阳极溶解，即腐蚀沿晶界Si粒子及Mg2Si粒子边缘的无沉淀带发展。Si粒子促进了腐蚀的发展，导致合金表现出严重的晶间腐蚀敏感性。
The potentiodynamic scanning curves and the electrochemical coupling behaviors of constituent phases at the grain boundary of Al-Mg-Si alloy were investigated. The corrosion mechanism of Al-Mg-Si alloys different ratio of Mg to Si was analyzed. The results show that the Si particle is cathodic to the Al-base and causes the anodic dissolution of Al-base at its adjacent periphery. At the beginning, the precipitate of Mg2Si is anodic to the Al-base and corrosion occurs on its surface. However, during its corrosion process, its potential moves to a positive direction with immersion time increasing, due to the preferential dissolution of Mg and the enrichment of Si, which makes Mg2Si become cathodic to Al- base and leads to the anodic dissolution of the Al-base at its adjacent periphery at a later stage. At the grain boundary of Al-Mg-Si alloys with a ratio of Mg to Si higher than 1.73, the Mg-and-Si contained precipitates are distributed discontinuously, resulting in that they are not sensitive to intergranular corrosion. There exist Mg-and-Si-contained precipitates and Si particles at the grain boundary of Al-Mg-Si alloys with a ratio of Mg to Si less than 1.73, corrosion occurs firstly on the surface of Mg2Si. Meanwhile, the Si particle leads to the great anodic dissolution of the precipitate-free-zone(PFZ) at its adjacent periphery. The Si particle also accelerates the preferential dissolution of Mg in Mg2Si precipitate, expediting the polarity transformation between Mg2Si and the PFZ. As a result, the corrosion development along the PFZ at the adjacent of Mg2Si particle is enhanced.
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