Abstract
The effects of the grain boundary precipitation on intergranular corrosion behavior were investigated by exfoliation tests and complementary techniques like scanning electron microscope (SEM), optical profilometry (OP), transmission electron microscope together with energy dispersive spectroscopy (TEM-EDS), and atomic force microscope (AFM). The results reveal the influencing mechanism of intergranular corrosion behavior from grain boundary precipitates (GBPs). The potential discrepancy between GBPs and adjacent areas induces corrosion cavity germination along the grain boundary. Furthermore, the increase of both active Mg and Zn content in GBPs improve the potential difference, which aggravates the intergranular corrosion cavity germination. However, the increment of noble Cu content in GBP is beneficial to reduce the potential difference. On the other side, the distribution of the continuous precipitates in the grain boundary region helps the initial corrosion cavities to connect, which improves the growth of intergranular corrosion cracks. Additionally, discontinuous GBPs and precipitation free zone (PFZ) hinder the spread and connection of intergranular corrosion cavities. Therefore, 7050 aluminum alloy forming different grain boundary precipitation characteristics after different aging treatments shows different resistance to intergranular corrosion: peak-aging < under-aging < over-aging.
Highlights
7050 Al alloys as one high-strength Al alloys are extensively used for the aerospace industry owing to their precipitation hardening behavior [1,2,3]
We systematically investigated the effect of grain boundary precipitates on the intergranular corrosion behavior of 7050 aluminum alloys
In 7xxx series Al alloys, the corrosion cavities prefer to conceive along the grain boundary, which is mainly controlled by the precipitates feature in the grain boundary region [32]
Summary
7050 Al alloys as one high-strength Al alloys are extensively used for the aerospace industry owing to their precipitation hardening behavior [1,2,3]. It is important to investigate the influence mechanism on intergranular corrosion of 7050 Al alloys from precipitation through quantitatively analyzing alloy element distribution and electricpotential discrepancy in the grain boundary region, which helps us to deeply understand the correlation between the grain boundary precipitation and intergranular corrosion behavior. Based on these experiments, the optimum heat treatment process for 7050 Al alloys with excellent intergranular corrosion resistance could be obtained
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