Laser additive manufacturing of carbon nanotubes (CNTs) reinforced aluminum matrix nanocomposites: Processing optimization, microstructure evolution and mechanical properties

In this study, a laser-based additive manufacturing route of selective laser melting (SLM) was applied to fabricate carbon nanotubes (CNTs) reinforced Al-based nanocomposites with tailored microstructures and excellent mechanical properties. The densification behavior, microstructure features and mechanical properties were investigated and the relationship between process and property was established. The results showed that the applied laser power and scan speed were the governing factors of the densification behavior of SLM-processed Al-based nanocomposites. SLM processing of 0.5 wt.% CNTs/AlSil0Mg nanocomposite powder led to the formation of three typical microstructures including the primary Al9Si cellular dendrites decorated with fibrous Si, the in situ Al4C3 covered on CNTs, and the precipitated Si inside the cellular grains. As the optimal SLM processing parameters of laser power of 350 W and scan speed of 2.0 m/s were applied, the fully dense SLM-processed CNTs/Al-based nanocomposites exhibited high microhardness of 154.12 HV0.2, tensile strength of 420.8 MPa and elongation of 8.87%, due to the formation of high densification and ultrafine microstructure. The grain refinement effect, Orowan looping system and load transfer are considered as three strengthening mechanisms occurred simultaneously during tensile tests, leading to excellent mechanical properties of SLM-processed CNTs/Al-based nanocomposites.