F. Viejo

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.

Effect of Reinforcement Coating on Corrosion Behavior of AA6061/SiC/20p Composite in High Relative Humidity Environments

Abstract A study of the influence of silicon dioxide (SiO2) active coatings on silicon carbide (SiC) reinforcement particles of an aluminum metal composite, AA6061 (UNS A96061)/SiC/20p (Al-Mg-Si alloy reinforced with 20 vol% of SiC particles), exposed to a high relative humidity environment (98% RH and 50°C), was carried out under simulation in a climatic chamber. To improve processibility, SiC particles were coated prior to composite manufacture by a casting procedure, using the sol-gel technique. The corrosion resistance of the composites was analyzed to determine the influence of the manufacturing variables. The nature of corrosion products before and after accelerated testing was analyzed by scanning electron microscopy (SEM) and low-angle x-ray diffraction (XRD), determining the influence of microstructural changes on corrosion behavior during exposure to the aggressive environment. The kinetics of the corrosion process was characterized on the basis of gravimetric tests. The corrosion damage to comp...

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.

Improvement of Corrosion Behavior of Aluminum Alloy/Silicon Carbide Composites with Lanthanum Surface Treatments

Abstract The effect of lanthanum-based conversion or electrolysis coating on the corrosion resistance of metal matrix composites consisting of Al alloy A3xx.x and silicon carbide (SiC) particles was investigated. Lanthanum-treated surfaces had better corrosion behavior in chloride media than original composite surfaces without treatment. Both treatments preferentially covered the intermetallic compounds and SiC particles. The electrolysis afforded a higher degree of protection compared to the conversion treatment because the coating was more extensive. The coating microstructure and nature of corrosion products were analyzed using scanning electron and atomic force microscopy (SEM and AFM), and low-angle x-ray diffraction (XRD).

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.

Influence of Reinforcement Content and Matrix Composition on the Oxidation Resistance of Aluminum-Matrix Composites (A3xx.x/SiCp)

A study was made on the influence of the SiCp proportion and the matrix concentration of four composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) on their oxidation behavior. Gravimetric tests were used in a kinetics study of the corrosion process at different temperatures (350, 400, 450, and 500°C). The influence of corrosion on mechanical properties was evaluated by hardness measurements. The nature of corrosion products and the influence of the microstructure on the morphology and growth of the oxidation layer were analyzed by SEM and low-angle XRD. The extent of the damage due to oxidation for Al/SiCp composites increases with the SiCp concentration due to the increase of nucleation sites. One of these nucleation sites is in the interface region between the matrix and the particles. Oxidation was influenced more by the percentage of alloy elements in the matrix than by the proportion of SiCp reinforcement. The presence of Cu and Ni in the matrix favors the oxidation process through the formation of different intermetallic compounds.

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.