Influence of Carbon Nanotubes on Mechanical Properties of Cast Aluminum, Grade A5

Abstract

Composite materials on the basis of A5 aluminum containing 0.01–0.1 wt % of carbon nanotubes (CNT) were obtained. The composite materials were fabricated by sand casting. Carbon nanotubes were added to the aluminum melt in the form of powdered mixture preliminarily produced using an AGO2S planetary ball mill. It was demonstrated that the CNT additions improved the ultimate tensile strength and yield strength of cast metal by 9 and 32%, respectively. The improvement of metal strength properties even at such a minor amount of nanotubes is determined not only by the inoculating effect but also by dispersion, dislocation, and, to a lesser extent, by reinforcing mechanisms of strengthening. For CNT content in aluminum equal to 0.01 wt %, the calculated yield strength agrees well with experimental values, whereas for CNT content equal to 0.05 and 0.1 wt %, the obtained strengthening is significantly lower than calculations, which can be attributed to agglomeration of nanotubes. The degree of conversion of carbon nanotubes into aluminum carbide as a consequence of interaction with aluminum melt is analyzed. It is demonstrated that less than 50% of carbon nanotubes are transformed into aluminum carbide during melting at 700–800°C. The fact that CNTs are not completely converted into carbide can be attributed to the fact that CNTs are arranged into bundles and only top layer of CNTs is in contact with the melt.