Additively manufactured high-performance AZ91D magnesium alloys with excellent strength and ductility via nanoparticles reinforcement

High-performance lightweight magnesium matrix composites (MMCs) play an important role in reducing CO₂ emissions in the context of carbon neutrality. In order to promote the widespread applications of MMCs, academic research on the design and fabrication of MMCs has increased dramatically over the past decade. However, it is extremely challenging to prepare MMCs with conventional techniques. In this study, nearly-dense nanoparticles modified AZ91D composites containing 2 wt. % nano-TiCN were manufactured by laser powder bed fusion (L-PBF) technology. The influence of nano-TiCN on the L-PBF processability, microstructure evolution, tensile properties, and underlying mechanisms of TiCN/AZ91D composites were systematically investigated. Results demonstrate that a suitable amount of nano-TiCN introduced to AZ91D can improve densification, restrict growth and refine the size of α-Mg and β-Al₁₂Mg₁₇, and introduce more crystallographic defects. Consequently, the as-deposited TiCN/AZ91D composites exhibit excellent strength without compromising ductility (ultimate tensile strength of ∼361 MPa and elongation up to ∼8.9 %), which are far superior to those of most previously reported L-PBFed Mg alloys and MMCs. The underlying mechanisms for strength enhancement are mainly ascribed to the decreased volumetric porosity, grain boundary strengthening through the refined grain, dislocation strengthening due to local mismatch stress, as well as Orowan strengthening via intragranular nano-TiCN. The excellent ductility is mainly attributed to delayed void nucleation by decreased defects, grain refinement, homogenous and refined β-Al₁₂Mg₁₇, and improved dislocation plasticity by well-dispersed nano-TiCN. This study thus sheds new light on fabricating high-performance MMCs with complex geometry by L-PBF.