Impact of cooling rate on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy

The impact of cooling rate after solution heat treatment on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy was investigated by accelerated immersion and electrochemical impedance spectroscopy test, optical microscope, electron backscatter diffraction and scanning transmission electron microscope. With the decrease of cooling rate from 1700 °C/s to 4 °C/s, exfoliation corrosion resistance of the aged specimens decreases with rating changing from EA to EC and the maximum corrosion depth increasing from about 169.4 µm to 632.1 µm. Exfoliation corrosion tends to develop along grain boundaries in the specimens with cooling rates higher than about 31 °C/s and along both grain boundaries and sub-grain boundaries in the specimens with lower cooling rates. The reason has been discussed based on the changes of the microstructure and microchemistry at grain boundaries and sub-grain boundaries due to slow cooling.