Combined Effects of Nb Content, Thermal Parameters, and Dendritic Scale Length on Electrochemical Corrosion in Horizontally Solidified Al3CuxNb Alloys

In this work, the effects of thermal solidification and microstructural parameters, such as solidification rate (V_L), cooling rate (T_R), and secondary dendritic spacing (λ₂), were studied on the electrochemical parameters of corrosion potential (E_CORR), current corrosion resistance (I_CORR), and polarization resistance (R_P). The alloys were solidified in a horizontal solidification device and two as-cast samples from the heat transfer surface were subjected to electrochemical polarization and impedance techniques. It was verified that the experimental values found for E_CORR were relatively close for all the investigated alloys and in both analyzed positions, allowing to deduce that the V_L, T_R and λ_2, as well as the Nb content had little influence, but enough to lead to different behavior in the I_CORR and R_P. For the alloy with 0.5wt.%Nb, higher V_L and T_R values, and smaller λ₂ resulted in lower I_CORR values. On the other hand, for alloys with 3 and 5wt.%Nb, coarser microstructures (greater λ₂) have lower corrosion rates. Microstructural analysis showed that Nb acts as a protective element against corrosive actions in the dendritic matrix.

Keywords:
Al-Cu-Nb alloys; Solidification thermal parameters; Microstructure; Corrosion resistance