Effect of nitrogen concentration on microstructure and mechanical properties of AlSi10Mg matrix composites fabricated by laser powder bed fusion

In this paper, a new way for synthesising nanoscale AlN and Si3N4 co-reinforced aluminium matrix composites (AMCs) by means of laser powder bed fusion (LPBF) is presented. The method entails irradiating AlSi10Mg powder with a laser beam, thereby forming an Al matrix melt pool in an atmosphere of dilute nitrogen (N2) concentration; simultaneously, the nearby N2 undergoes pyrolysis, generating reactive nitrogen ions that react with dissolved Al and Si atoms within the melt pool to form AlN and Si3N4 precipitates. Benefiting from rapid solidification characteristic of LPBF, these nitrides nucleate and grow in an extremely short temporal window before precipitating in the melt pool. Finally, the (AlN + Si3N4)/AMC is fabricated through successive layer-by-layer application of this synthesis strategy. Herein, a comparative investigation was conducted between AMCs processed under varying N2 concentrations (2 vol%, 5 vol%, and 10 vol%) and a reference AlSi10Mg alloy produced in a pure argon (Ar) atmosphere (0 vol% N2). Multiple analytical techniques (XRD, SEM, EDS, HR-TEM, and XPS analyses) verified nitrides incorporation into the AMCs matrix, meanwhile, EBSD characterised the grain morphology, dimension, and orientation. The strengthening–toughening mechanisms of the composites were systematically elucidated through comprehensive microstructural and mechanical property evaluations.