In-situ synthesis of aluminum matrix nanocomposites by selective laser melting of carbon nanotubes modified Al-Mg-Sc-Zr alloys

Abstract Aluminum matrix nanocomposites were manufactured by selective laser melting (SLM) of 0.5 wt% multi-walled carbon nanotubes (MWCNTs) modified Al-Mg-Sc-Zr alloys. The influence of MWCNT addition on the manufacturing quality, the phase formation and the mechanical properties of the Al-Mg-Sc-Zr alloys was investigated. It is found that primary Al3(Sc,Zr) particles precipitated and were uniformly dispersed in both equiaxed and columnar regions of the SLM-fabricated MWCNTs/Al-Mg-Sc-Zr nanocomposites. New Al4C3 phase was generated either on the open tip or in the defected and amorphous carbon layer of the MWCNTs, covering their overall surface. The unreacted MWCNTs completely transferred to Al4C3 upon heat treatment, forming a stable {003} Al4C3/{200}Al interface. The heat-treated MWCNTs/Al-Mg-Sc-Zr nanocomposites exhibit high microhardness of 169.0 ± 0.7 HV0.2, tensile strength of 544.2 ± 6.8 MPa, yield strength of 505.1 ± 6.3 MPa and elastic modulus of 97.8 ± 0.7 GPa, increasing by 6.3%, 4.5%, 5.0% and 5.6%, respectively, compared with the unmodified Al-Mg-Sc-Zr alloys. The improved performance was ascribed to the collective effects of precipitation strengthening of secondary Al3(Sc,Zr) nanoparticles, in-situ synthesis of Al4C3 as well as favorable interfacial bonding for effective load transfer. This study can provide reference values for laser additive manufacturing of MWCNTs modified other metallic alloys to enhance their comprehensive properties.