Electrochemical analysis of SiC composite additions at 7.5% weight content on the corrosion resistance of monolithic aluminium alloy in sulphate–chloride solution

Abstract

Effect of specific SiC particle sizes on the corrosion resistance and metastable pitting behaviour of AA1060 aluminium at 7.5% SiC weight content in 0.05 M H2SO4, 0.3 M NaCl and 0.05 M H2SO4/0.3 M NaCl solution was studied with potentiodynamic polarization, open circuit potential measurement and optical microscopy. SiC slightly increased the susceptibility of aluminium matrix composite (AA1060/SiC) at 9 μm and 29 μm in H2SO4 and NaCl solutions. The lowest corrosion rate values were observed at 3 μm and 45 μm SiC particle size. Two metastable pitting portions were visible on the polarization plots at these particles sizes due to passivation and re-initiation of transient corrosion pits. The metastable pitting portion of the polarization plots for AA1060/SiC in H2SO4 varied over wider corrosion potential and higher corrosion current compared to the plots from NaCl solution. The relatively smooth transition of the polarization plots in NaCl from anodic polarization to metastable pitting activity of the matrix composite resulted in more concentrated localized corrosion. The effect of SiC particle sizes in the admixed H2SO4–NaCl solution significantly contrasts the earlier observations. The OCP plots in H2SO4 and NaCl solution shows AA1060/SiC at 45 μm was most electropositive due to the combined action of the protective oxide from aluminium and insulating properties of SiC. The plots at 0 μm for both solutions were comparatively electronegative. Morphological damage of AA1060/SiC at 0 μm was significantly more than the deterioration at 3 μm and 45 μm. Keywords: Pitting, Corrosion, SiC, Aluminium