Impact of varying volume fraction of multi-walled carbon nanotubes to develop the microstructure and mechanical properties of friction stir processed Al-Cu alloy

In the present investigation, multi-walled carbon nanotubes (MWCNTs) were incorporated into AA2024-T351 alloy using groove method and successfully prepared the surface composites with the help of a solid-state technique named friction stir processing (FSP). Hardened steel having a tapered pin was used as a tool with 1400 rpm and a feed rate of 60 mm/min and tilt angle of 2°. The effect of MWCNTs with different volume fractions (2%, 4% and 6%) and without MWCNT relation to the base alloy was studied. The microstructural characteristics were studied by means of OM and FESEM with EDS analysis, and mechanical properties were examined. Among the evaluated composites in the AA2024 alloy with different proportions of MWCNTs, the 4% of the reinforcement achieved the optimum result. In comparison to AA2024-T351 alloy and FSPed of base metal, the combination of 4% of MWCNT reinforcement composites reduces the grain size to ∼6.5 µm under OM, which is 5.7 and 3.1 times smaller, and to ∼3.8 µm under FESEM, which is 8.2 and 3.9 times smaller respectively. Also, the better mechanical properties such as yield strength (∼398.7 MPa), ultimate tensile strength (∼585.7 MPa), elongation (∼12.3%), wear resistance (∼24.15 mm 3 /N-m) and micro-hardness (∼172.36 Hv) were 1.4, 1.2, 3.3, 2.9 and 1.5 times, respectively, superior to the base metal. The improvement of the microstructural grains and mechanical properties attributed to the fine dispersed MCWNTs into the base metal and better grain refinement. These composites are used in the application of aircraft structures, automobile sensitive components, thermal equipment and fabrication of hull structure and propulsion systems in the marine industry.