An investigation of microstructural basis for corrosion behavior of Al-CNT composites fabricated by SPS

Abstract

In this research effect of the addition of multi-wall carbon nanotubes (MWCNTs) as additive powder on microstructure and corrosion behavior of fabricated Al-CNT composites was studied. The aluminum powder and CNTs were mixed with high energy planetary ball-mill. It is observed that by increasing milling time, the uniformity of CNTs on aluminum matrix and consequently corrosion resistance of Al-CNT composite is increased. On the other hand, by increasing the volume percentage of CNTs, the uniformity of CNTs on aluminum matrix and corrosion resistance of fabricated Al-CNT composite is reduced. The value of polarization resistance, Rp, for fabricated composites with 2 % CNT is improved from 1.28 to 3.60 Ω/cm2 by increasing milling time. Also, the value of Rp for fabricated composites with 4 h milling time, is reduced from 3.60 to 2.76 Ω/cm2 by increasing the percentage of CNTs from 2 % up to 5 %. Moreover, Cyclic Polarization results showed that the pitting corrosion resistance improves by increasing milling time and deteriorates by increasing the percentage of CNTs. The electrochemical impedance spectroscopy (EIS) results showed that the corrosion mechanism of Al-CNT composites is a combination of uniform and pitting corrosion. Indeed, the CNTs act as preferred cathode regions and cause to formation of micro galvanic couples. The Al-2%CNT-4 h showed better uniformity and the highest corrosion resistance. The Al-5%CNT-2 h presented non-uniform distribution of CNTs and the lowest corrosion resistance.