Understanding the influencing mechanism of CNTs on the microstructure and mechanical properties of semi-solid stir casting Al-Cu-Mg alloys

Abstract

In this study, carbon nanotube (CNT) reinforced Al-Cu-Mg composites were fabricated by combining high-energy ball milling (HEBM) with semi-solid stirring casting technology (SSC). The effect of CNTs on the microstructural evolution and performance enhancement of hot extruded CNT/Al-Cu-Mg composites was investigated. SEM and XRD revealed that the addition of CNTs significantly refined the α-Al phase and suppressed its preferential growth in the (111) orientation. The microstructure of the hot-extruded composites was a heterostructure consisting of CNTs-rich fine-grained regions (1–5 μm) and CNTs-poor coarse-grained regions (7–20 μm). Additionally, CNTs were mainly distributed at the α-Al grain boundaries. Specifically, the higher the CNTs content, the higher the recrystallization degree of the composites. The tensile strength and yield strength increased from 319 MPa and 261 MPa to 523 MPa and 476 MPa, respectively, with CNT contents ranging from 0 to 1.5 wt.% owing to dislocation strengthening, grain refinement strengthening, load transfer strengthening, and second phase strengthening induced by CNTs.