Intergranular and Exfoliation Corrosion Behavior of Sc-Containing Al-Cu-Li-Zr Alloy

As a promising neotype high-mass structural material of wide acceptance in aerospace and aviation industries, Sc-containing Al-Cu-Li-Zr based alloy has outstanding mechanical properties, weldability, and corrosion resistance. Thus Al-3.5Cu-1.5Li-0.22(Sc+Zr) alloy was prepared making use of ingot metallurgy. The intergranular corrosion and exfoliation corrosion behavior of the resulting alloy subject to different modes of aging was investigated. The polarized curves of the alloy were measured, while the microstructures of the as-cast and corroded alloy were analyzed by means of scanning electron microscopy and transmission electron microscopy. It was found that the naturally-aged alloy had the best intergranular and exfoliation corrosion resistance. The intergranular and exfoliation corrosion of the alloy was accelerated with prolonging aging duration, which conformed to the relevant polarization test results of the alloy in a mixed acidic solution composed of 4.0 mol/L NaCl+0.1 mol/L HNO_ 3 +0.4 mol/L KNO_ 3 . In terms of the microstructure of the alloy, no Γ_ 1 phase was precipitated in the naturally-aged sample. Contrary to the above, a small amount of bar-like fine Γ_ 1 phase was precipitated in the under-aged sample whose Γ_ 1 phase coarsened with increasing aging duration. Moreover, some equilibrium phases and precipitation free zone (PFZ) were observed in the over-aged sample. Since the PFZ and Γ_ 1 phase had more negative open-circuit potentials than the Al matrix, they could act as anodes in corrosive media and be dissolved preferentially. This might account for the intergranular and exfoliation corrosion of the titled alloy.