Intergranular and exfoliation corrosion behaviors of 2A97 Al-Li alloy via thermal exposure

The effect of thermal exposure on the corrosion behavior of 2A97 Al-Li alloy was systematically investigated using electrochemical measurement, intergranular corrosion test, exfoliation corrosion test, and microstructural characterization. The results show thatthermal exposure leads to a progressive degradation of corrosion resistance for 2A97 Al-Li alloy, and thermal exposure temperature has a more obvious effect on its corrosion behavior than exposure time. With increasing thermal exposure temperature, the corrosion morphology changes from pitting corrosion to severe intergranular corrosion and deep exfoliation corrosion, accompanied by a significant increase in the corrosion depth and corrosion grade; moreover, the phase transformation from δ′ and θ′ phase into T1 phase is promoted during thermal exposure, and they are preferentially precipitated and coarsened along the grain boundaries; in addition, a large number of solute atoms are consumed because of the T1 phase growth, the precipitation free zones (PFZs) is continuously formed and widened at the grain boundaries, and then these PFZs act as anodic regions relative to the adjacent matrix. Therefore, the corrosion propagation is promoted along grain boundaries, and both intergranular corrosion and exfoliation corrosion are accelerated.