Effect of number of passes on the corrosion behavior of Fe/Al surface composites produced by plasma spraying and friction stir processing

Abstract

Friction stir processing (FSP) was applied on the surface of the low carbon steel substrate and the steels which coated by Al–30wt.% Fe with different (1–4) passes. Metallographic examinations and electron backscatter diffraction (EBSD) were used to analyze the microstructure of the stir zones (SZs). The influence of the number of FSP passes on electrochemical properties of the SZs in steels and the surface composites in 3.5wt.% NaCl solution was analyzed via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The Fe-Al intermetallics were produced in-situ on the surface of the composite layers during FSP. Widmänstatten ferrite plates were formed in the SZs of both groups of samples. The corrosion resistance of the FSPed steels was improved by increasing the number of passes due to the increment of grain size in SZs. Among the surface composites, the single-pass FSPed surface exhibited the highest polarization resistance and charge transfer resistance. This was attributed to the presence of elemental aluminum and Al-rich compounds at the surface.