M. Carboneras

Improvement of Corrosion Behavior of A3xx.x/SiCp Composites in 3.5 wt % NaCl Solution by Ce Surface Coatings

The effects of the silicon carbide particles (SiCp) proportion and the matrix composition of aluminum matrix composites (A3xx.x/ SiCp) modified by cerium-based conversion or electrolysis coating were evaluated in 3.5 wt %NaCI aerated solution. The intermetallic compounds were preferentially covered by cerium-based conversion coating obtained by immersion in 50°C solution of Ce(III) salt, and the intermetallic compounds, SiCp, and aluminum matrix were covered by electrolysis treatment performed in ethylene glycol monobutyl ether solution. The kinetic of the corrosion process was studied on the basis of gravimetric tests, and the corrosion process was evaluated by electrochemical impedance spectroscopy. The nature of both Ce coating and corrosion products was analyzed before and after accelerated testing by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and low-angle X-ray diffraction to determine the influence of microstructural changes on corrosion behavior during exposure to the corrosive environment. The corrosion process is influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement. Both cerium-treated surfaces present better behavior to chloride solution corrosion than original composite surfaces without treatment; however, electrolysis affords a higher degree of protection than the conversion treatment because the coating is more extensive.

Influence of SiCp content and matrix composition on corrosion resistance in cast aluminium matrix composites in salt fog

Abstract A study has been carried out into the influence of the proportion of SiCp and the matrix composition of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p and A380/SiC/20p) on their salt fog corrosion behaviour. The matrix of the A360/SiC/xxp composites is virtually free of Ni and Cu while the A380/SiC/xxp matrix contains 1.39 - 1.44 wt-%Ni and 3.13 - 3.45 wt-%Cu. The kinetics of the corrosion process were studied using gravimetric tests. The nature of corrosion products was analysed by SEM and low angle XRD before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The extent of the corrosion damage to the Al/SiC composites depended on the concentration of nucleation sites and the matrix composition. One of these nucleation sites is in the interface region between the matrix and the particles. The corrosion process was influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement.

Corrosion behavior of cast aluminum matrix composites (A3xx.x/SiCp) in chloride media

The influence of silicon carbide particles (SiCp) proportion and matrix composition of four aluminum metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) on their corrosion behavior in 1, 2, and 3.5 wt % NaCI solutions has been studied. The matrix of A360/SiC/xxp composites is virtually free of Cu whereas the A380/SiC/xxp matrix contains 1.39-1.44 wt % Ni and 3.13-3.45 wt % Cu. The kinetics of the corrosion process was studied on the basis of gravimetric tests and the corrosion process was evaluated by electrochemical impedance spectroscopy during immersion in NaCI solutions. The nature of the corrosion products was analyzed, before and after accelerated testing, by scanning electron microscopy and low angle X-ray diffraction, to determine the influence of microstructural changes on corrosion behavior during exposure to the corrosive environment. The extent of the corrosion damage of Al/SiC composites depends on the SiCp proportion, chloride ion concentration, and matrix composition. The preferential nucleation sites are located at the matrix/particle and matrix/intermetallic compound interfaces. The corrosion process is influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement. The corrosion product is a compact and stable Al 2 O 3 . 3H 2 O layer that protects materials against corrosion.

Corrosion of AISI 316 stainless steel containing Cu and Sn in acid media

Abstract The influence of Cu and Sn additions on the corrosion resistance of AISI 316 stainless steels has been evaluated in various acid media (boiling 50 wt-%H3PO4, boiling 65 wt-%HNO3, 3 wt-%HCl at 25°C and 30 wt-%H2SO4 at 50°C). A kinetic study of the corrosion process was carried out using gravimetric tests. The nature of the corrosion products was analysed by SEM, X-ray mapping and X-ray photoelectron spectroscopy both before and after accelerated corrosion tests. The steels displayed high chemical resistance to the nitric, hydrochloric and phosphoric acid media. An increase in Cu and Sn concentration did not significantly affect the corrosion resistance in boiling 50 wt-% phosphoric acid, boiling 65 wt-% nitric acid or 3 wt-% hydrochloric acid. The behaviour of AISI 316 in sulphuric acid solution was greatly improved by increasing the Cu concentration, whether alone or in combination with Sn. The effect of Sn addition in decreasing the corrosion rate was minor in comparison with that of Cu.