Understanding the influence of carbon addition on the corrosion behavior and mechanical properties of Al alloy “covetics”

The recent invention of a new processing method for metals and alloys involving the addition of carbon has led to several reports demonstrating an enhancement in the mechanical properties of the materials known as “covetics.” In this work the corrosion behavior and mechanical properties of a 6061 aluminum–carbon covetic are investigated and explained. Covetic samples with carbon added were found to exhibit a corrosion potential 40–70 mV higher than samples processed without the addition of carbon. However, the corrosion current density of the covetic with carbon added relative to samples without carbon added was also increased. Surface characterization following the corrosion testing using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction revealed significant differences between the covetic with carbon added and the covetic parent material processed without carbon addition. After corrosion, the surface of the covetic with carbon added showed a alloying element rich surface morphology from the parent alloy and exhibited a smaller grain size than the material processed without carbon. Additionally, changes in the mechanical properties of the covetic were observed with both the hardness and the compressive strength of the covetic increasing as a result of carbon addition. The observed change in corrosion behavior and mechanical properties of the covetic with carbon added, along with the physical characterization, are consistent with the formation of a secondary phase in the alloy induced by carbon addition during the process used to make the covetic.