Regulating microstructure, mechanical properties and electrochemical characteristic of 2024-CNTs aluminum composites via decorating nano Ni on the surface of CNTs

Abstract

CNTs are decorated uniformly with nano Ni through electroless plating method (CNTs@Ni). Average contact angle with 2024 aluminum alloy reduces from 138.6° to 81.2°, significantly improving wetting of CNTs. CNTs@Ni are used as the reinforcement to fabricate 2024-CNTs@Ni composites via high-intensity ultrasonic-assisted casting method. The appropriate content of CNTs@Ni assists 2024-CNTs@Ni composites to obtain excellent microstructure, mechanical properties and electrochemical corrosion resistance. When the CNTs@Ni content is 1.5 wt%, CNTs@Ni are uniformly dispersed, uniform organization and grain refinement is most significant according to the results of scanning electron microscopy. CNTs@Ni composites exhibit more excellent mechanical properties than cast 2024 aluminum alloy. This results from a synergy of grain refinement strengthening, thermal mismatch strengthening, Orowan strengthening and load-bearing strengthening. The percentage contribution of each strengthening mechanism is calculated for composites with different CNTs@Ni content. In addition, 2024–1.5 wt% CNTs@Ni composites show better electrochemical characteristic with higher corrosion potential of −603.792 mv and lower corrosion current density of 102.332 μA·cm−2. Cl− ions are more resisted because of Ni introduction. The large number of dislocations accelerates the diffusion of elements, which expedites formation of thicker protective films to resist corrosion. The phenomenon of “large anode - small cathode” improves the electrochemical corrosion resistance.