Relations between Microstructure and Exfoliation Corrosion Resistance of 7050 Al-alloy

doi:10.11902/1005.4537.2014.219

Journal of Chinese Society for Corrosion and protection

2015, Vol. 35

Issue (5): 423-428 DOI: 10.11902/1005.4537.2014.219

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Relations between Microstructure and Exfoliation Corrosion Resistance of 7050 Al-alloy

Feng ZHAO^1,²(

),Fayun LU^1,²,Nan MU^1,²,Fuan GUO^1,²,Li ZHANG¹

1. National Engineering Research Center for Plastic Working of Aluminium Alloys, Shandong Nanshan Aluminium Co., Ltd., Yantai 265713, China
2. Beijing Nanshan Institute of Aeronautical Materials, Beijing 100048, China

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Abstract

The microstructure characteristics, exfoliation corrosion behavior of 7050-T7451Al- alloy plates were examined by optical microscopy, scanning electron microscopy and Image Pro Plus. The effect of the distribution of grain boundary precipitates, the fraction of recrystallized grains and the length-width ratio of grains on the exfoliation corrosion behavior was investigated. The results indicate that the microstructures of the 7050-T7451 plates fabricated by different processes are composed of recrystallized grains and non-recrystallized grains with precipitates distributed discontinuously along grain boundaries; but which varied corresponding to the relevant fabrication processes. The average length-width ratio of grains plays an important role in the exfoliation corrosion process of the plate, while the influence of the discontinuity of precipitates distribution and the fraction of recrystallized grains is weak. When the precipitates distribute discontinuously along grain boundaries and the average length-width ratio of grains is less than 5, the EXCO resistance of 7050-T7451 plate can reach EA degree or better.

Key words: 7050-T7451 aluminum alloy exfoliation corrosion grain aspect ratio grain boundary precipitate

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Cite this article:

Feng ZHAO, Fayun LU, Nan MU, Fuan GUO, Li ZHANG. Relations between Microstructure and Exfoliation Corrosion Resistance of 7050 Al-alloy. Journal of Chinese Society for Corrosion and protection, 2015, 35(5): 423-428.

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https://www.jcscp.org/EN/10.11902/1005.4537.2014.219 OR https://www.jcscp.org/EN/Y2015/V35/I5/423

Fig.1 GBP characteristics of No.1 (a), No.2 (b) and No.3 (c) samples

Fig.2 Bright field OM images of the grains of No.1 (a, d), No.2 (b, e) and No.3 (c, f) samples

Fig.3 Characteristics of the grains in polarized light field (a~c) and graphs of grain aspect ratios (d~f) for No.1 (a, d), No.2 (b, e) and No.3 (c, f) samples

Fig.4 Surface appearances (a, c, e) and corrosion products (b, d, f) of No.1 (a, b), No.2 (c, d) and No.3 (e, f) samples after exfoliation corrosion for 48 h

Fig.5 OM micrographs of longitudinal sections of No.1 (a), No.2 (b) and No.3 (c) samples after exfoliation corrosion

Fig.6 Corrosion depths along the longitudial sections of No.1 (a), No.2 (b) and No.3 (c) samples after exfoliation corrosion

Fig.7 Mean grain dimensions and effect of grain shape on depths of EXCO in the top surface, 1/4 layer, 1/2 layer of 2014 alloy^[11]

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