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 (VL), cooling rate (TR), and secondary dendritic spacing (λ2), were studied on the electrochemical parameters of corrosion potential (ECORR), current corrosion resistance (ICORR), and polarization resistance (RP). 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 ECORR were relatively close for all the investigated alloys and in both analyzed positions, allowing to deduce that the VL, TR and λ2, as well as the Nb content had little influence, but enough to lead to different behavior in the ICORR and RP. For the alloy with 0.5wt.%Nb, higher VL and TR values, and smaller λ2 resulted in lower ICORR 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.