Carbon network/aluminum composite made by powder metallurgy and its corrosion behavior in seawater

Abstract

In this work, a carbon network/aluminum matrix composite material was made by the powder metallurgical approach. Pure aluminum powders with a diameter of less than 30 μm were compressed with sugar particles with the similar size under a pressure of 40 MPa. Sintering at 500 °C in pure argon gas for 2 h was performed to carbonize the sugar. After the sintered product was cooled down, microstructure analysis was carried out. It was found that high temperature sintering allowed the material to generate carbon networks distributed along the grain boundaries in the porous aluminum. An aluminum to sugar ratio of 1 to 1 reached the maximum carbon concentration in the composite for keeping the structural integrity. Characterization of the corrosion behaviors of the carbon network/porous aluminum composite material and a pure aluminum plate in seawater was conducted by measuring their Tafel plots. The Galvanic potential of the carbon network/porous aluminum composite material is about -0.62 V. The pure aluminum shows a more negative Galvanic potential of -0.755 V. As compared with pure aluminum, the composite material showed improvement on the corrosion property. The corrosion current of the composite in seawater is about 100 times lower than that of the pure aluminum. The existence of carbon network in the composite and the oxidized state of the sintered aluminum allows the composite material to be more corrosion resistant in seawater. For the materials processed with higher sugar content (with Al: sugar ratio of 1:1.25), carbon became the dominant phase in the composite. The material has a low strength and ease to get collapsed. The corrosion behavior of the composite made from low Al to sugar ratio raw material is similar to that of the one with Al: sugar ratio of 1:1. For the high carbon content composite material with Al: sugar ratio of 1:1.25, the Galvanic potential of the material is as high as -0.32 V, which is very close to the Galvanic potential of graphite in seawater. It shows the corrosion behavior of pure carbon in seawater.