Pitting Corrosion of 7020 Aluminum Alloy in 3.5%NaCl Solution

doi:10.11902/1005.4537.2016.023

Journal of Chinese Society for Corrosion and protection

2017, Vol. 37

Issue (3): 279-286 DOI: 10.11902/1005.4537.2016.023

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Pitting Corrosion of 7020 Aluminum Alloy in 3.5%NaCl Solution

Yun DAI^1,^2,³,Shengdan LIU^1,^2,³(

),Yunlai DENG^1,^2,³,Xinming ZHANG^1,^2,³

1 School of Materials Science and Engineering, Central South University, Changsha 410083, China
2 Key Laboratory of Nonferrous Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China
3 Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Centre, Changsha 410083, China

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Abstract

The pitting corrosion behavior of 7020 aluminum alloy in 3.5%(mass fraction) NaCl solution was investigated by immersion test and cyclic polarization curve, while the corrosion morphology of the alloy was characterized by means of optical microscopy (OM), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). The results show that the curve of maximum depth of corrosion pits versus time exhibits ''S''-like shape. α-AlFeSiMn phase may act as a local cathode, thereby de-alloying occurred around particles of α-AlFeSiMn phase, i.e. Al matrix nearby the particles of α-AlFeSiMn phase was dissolved due to its anode nature, while Mn-and Cr-containing precipitates in the matrix may fall off along with the dissolved Al. Pitting susceptibility reduces in the later stage of corrosion due to that the formed corrosion products may act as a protective barrier for the alloy to some extent.

Key words: 7020 aluminum alloy pitting corrosion corrosion dynamics second phase cyclicpolarization curve

Received: 04 February 2016

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Cite this article:

Yun DAI,Shengdan LIU,Yunlai DENG,Xinming ZHANG. Pitting Corrosion of 7020 Aluminum Alloy in 3.5%NaCl Solution. Journal of Chinese Society for Corrosion and protection, 2017, 37(3): 279-286.

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https://www.jcscp.org/EN/10.11902/1005.4537.2016.023 OR https://www.jcscp.org/EN/Y2017/V37/I3/279

Fig.1 SEM image (a) and EDS result (b) of second phase in 7020 aluminum alloy

Fig.2 HAADF image (a) and EDS result (b) of dispersed phase in 7020 aluminum alloy

Fig.3 OM images of 7020 aluminum alloy after immersion for 168 h (a), 504 h (b), 840 h (c) and 1176 h (d)

Fig.4 Cross section of 7020 aluminum alloy after immersion for 1176 h (a) and the magnified image of the square area in Fig.4a

Fig.5 Corrosion dynamics curve of maximum pitting corrosion depth vs time

Fig.6 SEM images of 7020 aluminum alloy after immersion for 168 h (a), 504 h (b), 840 h (c) and 1176 h (d)

Fig.7 SEM images (a, c) and EDS results (b, d) of 7020 aluminum alloy after immersion for 168 h (a, b) and 1176 h (c, d)

Table 1 Chemical compositions of the second phase in 7020 aluminum alloy after immersion for different time(mass fraction / %)

Fig.8 Polarization curves of 7020 aluminum alloy after immersion for different time

Table 2 Polarization characteristics for 7020 aluminum alloy after immersion for different time

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