Characterization of Al-20Si-5Fe/CNT metal matrix composite produced by ball milling technique

Carbon nanotubes (CNT) are an extraordinary discovery in nanotechnology science. They have remarkable material features such as high surface-to-volume ratio, high tensile strength, high thermal conductivity, and low density. Carbon nanotubes are many times harder and yet lighter than all metals, and thus a good candidate for reinforcing them. In this research, Al-20Si-5Fe/xCNT (x=0.5 and 1 wt.%) metal matrix composites, which have been used in automotive and aerospace industry in recent years, were produced by ball milling technique. The effect of milling time and CNT content on the crystal structure, particle morphology, microstructure, particle size and mechanical properties of the material was investigated. X-ray diffraction analyzes showed that the width of aluminum peaks increase due to the decrease in crystallite size and the increase in lattice strain. From the scanning electron microscope images, it was observed that the powders tended to agglomerate at the early stages of milling and decreased in particle size with a more homogeneous distribution after 240 min. of milling time. Energy dispersive X-ray mapping images revealed that the coarse silicon particles fragmented into fine particles at 30 min. of milling time, while the fragmentation in iron particles began after 240 min. of milling time. The particle size distribution analyzes showed that the three-modal distribution seen in unmilled powders was transformed into a one-modal distribution with increasing in milling time. Also, CNT addition showed a positive effect on particle size refinement. From the depth sensing indentation analyses, the hardness and reduced elastic modulus of the composite materials were increased with increasing milling time. The addition of CNT also improved the mechanical properties of composite materials. A new model was proposed to explain this improvement in mechanical properties.