Understanding the Influencing Mechanism of CNTs on the Microstructures and Wear Characterization of Semi-Solid Stir Casting Al-Cu-Mg-Si Alloys

In this study, CNTs-reinforced Al-Cu-Mg-Si nanocomposites were successfully fabricated by high-energy ball milling (HEBM) combined with semi-solid stir casting. Then, the composites were subjected to hot extrusion. The Microstructure and Phase analysis of the CNT/Al-Cu-Mg-Si composites were characterized by an Optical microscope, Scanning Electron Microscope (SEM), and XRD. Additionally, density, hardness, and wear were measured. The results revealed that the addition of CNTs effectively inhibited the growth of alpha-Al grains, and the grains were dramatically refined. Additionally, the dynamic recrystallization degree of the composite extruded rod gradually increased from 1.3% to 68.4%, with the content of CNTs from 0 wt% to 3.0 wt%. The hardness values of the composite increased with an increase in CNTs. Moreover, the friction factor and wear rate of the composites first decreased and then increased as the content of CNTs increased. When 1.5CNTs were added, the friction coefficient (COF) and wear rate of composites reached the minimum of 0.3577 and 3.42 mg/km, which were reduced by 30.09% and 73.03% compared with Al-Cu-Mg-Si alloy, respectively.