Study on the quenching sensitivity of corrosion properties in 7199 aluminum alloy

This study used electrochemical corrosion, intergranular corrosion (IGC), and exfoliation corrosion tests, as well as microscopic observations of the microstructure and first-principles calculations, to investigate the effect of different quenching rates on the microstructure and corrosion properties of the 7199 alloy. The results show that as the quenching rate decreases, the size, Zn, and Mg content of precipitated phases at grain boundaries (GBs), as well as the width of the precipitation-free zone (PFZ), increase, resulting in a decrease in corrosion properties. During slow quenching, the η phase (MgZn2) at the GBs continuously absorbs surrounding Zn and Mg atoms, causing Zn and Mg atom depletion near the GBs. This results in the formation of a wide PFZ. Enlargement of the η phase and PFZ at the GBs leads to anodic dissolution channels, allowing for rapid corrosion expansion along the GBs. Additionally, at slow quenching rates, not only does the η phase precipitate at the subgrain boundaries (SGBs) but also the T and S phases. In corrosive environments, the η phase is more prone to corrosion than the T and S phases. Electron work function calculations show that the S phase has the highest corrosion potential, whereas the η phase has the lowest. As a result, SGBs containing T and S phases are unlikely to serve as corrosion pathways. Corrosion preferentially extends along SGBs containing η phases.