Improving the corrosion resistance of 7055 alloy by manipulating passivation film through trace addition of TiB2 nanoparticles

Abstract

In this study, 7055 alloy inoculated by a minor addition of TiB2 nanoparticles was prepared and subjected to passivation treatment. The microstructures, pitting behaviors, and electrochemical properties of the 7055-0.5TiB2 composite were comparatively investigated with respect to the base alloy. The results show that the incorporation of 0.5 wt% TiB2 nanoparticles refines the grain size (from 142.4 μm to 44.1 μm) and reduces the volume fractions of the residual intermediates from 0.59 % to 0.49 %, leading to an increased thickness (from 4.05 nm to 5.95 nm) and improved homogeneity of the passivation film. Both the pitting diameter and the pitting area fractions are reduced upon immersing in 3.5 % NaCl for 24 h. Electrochemical test results show that the values of passivation layer resistance, charge transfer resistance, and polarization resistance are significantly increased, while the corrosion current is reduced after the incorporation of TiB2 nanoparticles, confirming the formation of a more effective barrier layer, i.e., the passivation film. The improved corrosion resistance of 7055 alloy with the incorporation of TiB2 nanoparticles is attributed to the reduced active dissolution rate in the grain boundary region and a more uniform and thicker passivation film with a lower corrosion rate.