CORROSION OF AN Al-Mg-Si ALLOY UNDER MgCl2 SOLUTION DROPS THROUGH KELVIN PROBE

J Chin Soc Corr Pro

2011, Vol. 31

Issue (6): 467-472 DOI:

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CORROSION OF AN Al-Mg-Si ALLOY UNDER MgCl₂ SOLUTION DROPS THROUGH KELVIN PROBE

CAI Chao¹, YANG Jianfeng¹, LI Jinfeng², ZENG Fengli², TAN Xing²

1. State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049
2. School of Materials Science and Engineering, Central South University, Changsha 410083

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Abstract The corrosion behavior of Al-0.63Mg-0.28Si alloy under MgCl₂ solution drops with initial concentration of 0.05 mol/L~0.3 mol/L and volume of 6 μL in the environment of relative humidity (RH) 75% and RH 33% were studied by using Kelvin Probe. In these two environments, because the water in the drop is evaporated, a thin MgCl₂ solution layer with a diameter of about 2.9~3.2 μm forms on the alloy surface. As the open circuit potential (OCP) baseline keeps stable at -0.3~-0.5 V_vs \ SHE, there exists potential noise that the OCP repeatedly exhibits a sudden decrease and then immediate recovery, which is associated with initiation and re-passivation of metastable pits with diameter less than 3 μm. When the OCP baseline decreases slowly to -0.7~0.8 V and keeps stable low, stable filiform-like corrosion occurs and develops. In the environment of RH 33%, only metastable pitting corrosion occurs within 24 h. In the environment of RH 75%, as the initial MgCl₂concentration is 0.3 mol/L and 0.2 mol/L, the main corrosion form is metastable pitting corrosion. As the initial concentration is reduced to 0.1 mol/L, stable filiform-like corrosion always occurs on the drop edge and grows outward. As the initial concentration is further decreased to 0.05 mol/L, the likelihood of stable corrosion is lowered, and the main corrosion form is metastable pitting corrosion within 24 h. The number of metastable pits every unit time is increased with RH of the environment. Meanwhile, in environment of the same RH, it is increased with the decrease in initial concentration.

Key words: Al-Mg-Si alloy Kelvin probe (KP) MgCl₂ solution drop

Received: 10 September 2010

ZTFLH:

TG172

Corresponding Authors: LI Jinfeng E-mail: lijinfeng@csu.edu.cn

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CAI Chao, YANG Jianfeng, LI Jinfeng, ZENG Fengli, TAN Xing. CORROSION OF AN Al-Mg-Si ALLOY UNDER MgCl₂ SOLUTION DROPS THROUGH KELVIN PROBE. J Chin Soc Corr Pro, 2011, 31(6): 467-472.

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https://www.jcscp.org/EN/ OR https://www.jcscp.org/EN/Y2011/V31/I6/467

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