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PurposeThe research work in this paper aims to focus on understanding the corrosion inhibition of 6061‐8 (vol.%) SiC in 3.5 per cent NaCl solution using different concentrations (250, 500, 750 and 1,000 ppm) of cerium and lanthanum chloride.Design/methodology/approachThe corrosion inhibition of 6061‐SiC in 3.5 per cent NaCl solution using the rare earth chloride inhibitors was analyzed by different electrochemical techniques. The techniques employed were linear polarization, Tafel extrapolation and electrochemical impedance spectroscopy (EIS). Further, surface characterization, before and after inhibitor addition, was studied using scanning electron microscopy (SEM) and energy dispersive analysis using X‐ray.FindingsIt was observed that the polarization resistance increased after addition of LaCl3 and CeCl3, with maximum increase noticed for 250 ppm LaCl3 and 1,000 ppm CeCl3. CeCl3 addition showed better improvement in polarization resistance value compared with LaCl3 addition. Pitting nucleation resistance also increased with addition of LaCl3 and CeCl3, with maximum obtained for 250 ppm LaCl3 and 500 ppm CeCl3. EIS studies showed that there was a significant increase in resistance of areas not covered by the surface film after addition of LaCl3 and CeCl3, when compared with the case without inhibitor, with a maximum increase observed with 1,000 ppm CeCl3. Rare earth chloride addition resulted in an increase in resistance on both cathodic intermetallic sites as well as the pitted regions by formation of precipitates of their oxide/hydroxide on those locations. This gave the high pitting nucleation resistance as well as improved corrosion resistance.Research limitations/implicationsIt was observed that optimum concentrations of CeCl3 and LaCl3 resulted in good corrosion resistance properties on 6061‐SiC in 3.5 per cent NaCl solutions. Even small quantities of these inhibitors resulted in high corrosion resistance. However, it should be noted that both LaCl3 and CeCl3 did not follow a simple increase in corrosion resistance with composition, despite both being rare earth chloride inhibitors, and this issue merits further research.Practical implicationsMetal matrix composites (MMC) are of great use in the aerospace, military and automotive industries due to their good mechanical strength/density and stiffness/density ratios. A typical example might be the reinforcement of Al alloys with SiC particulates, which leads to a new generation of engineering materials. However, the addition of a reinforcing phase can cause discontinuities in any protective surface film, increasing the number of sites where corrosion can be initiated and rendering the composite liable to severe attack. Thus, this research work was performed to investigate if a suitable concentration of lanthanide salts (LaCl3 and CeCl3) could be identified that could improve both uniform and pitting corrosion resistance.Originality/valueEarlier studies on the corrosion inhibition of 6061‐SiC used cerium conversion coatings. More recently (i.e. during the la...

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A corrosion model was developed to correlate the atmospheric corrosion rates of 50 volume% nickel (Ni)-coated carbon (C) fiber reinforced pure aluminum (Al (99.99%)/C/50f) metal-matrix composites (MMCs) to weather and environmental parameters such as chloride (Cl − ) deposition rate, aerosol pH, and the percentage of time wet (Q4). The model was developed using polarization data of Al and C in solutions of various pH levels and Cl − concentrations. The polarization data indicated that the galvanic corrosion current (i galv ) between Al and C is a function of Cl − concentration and pH. There was a linear relationship between the logarithm of i galv and the logarithm of Cl − concentrations in neutral solutions with an R 2 value close to 0.95. Using the linear relationship, a corrosion model was developed that estimated the atmospheric corrosion rate of Al (99.99%)/50 MMCs as a function of the Cl − deposition rate and Q4 (i.e., [Cl - Compared to monolithic Al alloys, Al/C MMCs offer lower density and superior properties such as high specific strength and stiffness, good wear resistance, and low to zero coefficient of the thermal expansion. [1][2][3][4] Due to their unique properties, Al MMCs have received increased attention as an attractive choice in the automotive, defense, and aerospace industries. For example, Al/C MMCs have been used for antenna waveguide mast in the Hubble Space Telescope, 1,5 electromagnetic interference shielding in electronics 6 structural radiators in space applications, 5,7 and electronic packaging. 6,8,9 Al/C MMC wires are being explored to replace the steel-core Al-clad wires as the strength carrying members in aluminum electrical transmission lines as they offer higher electrical conductivity and low sag characteristics (due to their low CTE) when temperatures rise due to increased power transmission. 10,11 The high electrical conductivity of C, however, makes Al/C MMCs much more susceptible to corrosion due to the galvanic effect between the C fiber and the Al matrix. Galvanic couplings in A 356 Al alloy and graphite MMC (Al 356/Gr) by Kendall and Dull,12 Al 6061 reinforced with 30% C MMC (Al 6061/C/30f) by Dull and Harrigan, 13 Al (LM 13)/C/3f, AS7G0.6/C by Payen et al., 14 and Al 2024/C MMCs by Saxena, Prasad, and Dan, 15 were investigated in NaCl solutions. The presence of crevice corrosion along the region of high fiber densities was recognized as signs of galvanic coupling between the C fiber and Al matrix. 12,13 Payen et al., showed that the C fiber and Al matrix interface served as preferential sites for corrosion using long focal video microscopy. 14 Galvanic corrosion occurred between Al 2024 and graphite particles not only in NaCl but also in HCl, HNO 3 , H 2 SO 4 , HClO 4 acids. 15 Hihara and Latansion, 16 measured the galvanic corrosion current density and the galvanic potential between the graphite fiber and the Al 6061 matrix, using the zero-resistance ammeter (ZRA) in both 0.5 M Na 2 SO 4 and 3.15% NaCl solutions where the galvanic current in NaCl solution was signifi...

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