Microstructure and mechanical properties of graphene and nano-zirconia reinforced AlSi10Mg composite fabricated by laser powder bed fusion

In this work, the graphene nano-platelets (GNPs) and ZrO₂ nanoparticles single- and hybrid-reinforced AlSi10Mg composites were fabricated by laser powder bed fusion (LPBF). The influences of the introduction of single and hybrid reinforcements on the microstructure and tensile properties were investigated. Furthermore, the strengthening and toughening mechanisms of the LPBF-ed composites were systematically discussed. The results shows that the addition of the hybrid reinforcement (GNPs + ZrO₂) reduces grain size of composites more effectively than the addition of either reinforcement alone. The GNPs and ZrO₂ nanoparticles promote the columnar-to-equiaxed transition of α-Al grains at the bottom of the melt pool during LPBF processing of single- and hybrid-reinforced composites, resulting in a bimodal microstructure. The hybrid-reinforced composites had the greatest volume of fine equiaxed grains. There are several reinforcing phases in the (GNPs + ZrO₂)/AlSi10Mg composite: eutectic Si phase distributed along cell boundaries, large numbers of un-melted GNPs and ZrO₂ nanoparticles uniformly distributed along cell and grain boundaries, Si precipitate and some un-melted ZrO₂ nanoparticles inside the cells, as well as rod-like Al₄C₃ nanoparticles distributed along cell boundaries. Compared to the single modified composites, the (GNPs + ZrO₂)/AlSi10Mg composite had a highest tensile strength of 520 ± 12 MPa however the lowest elongation of 8 ± 1.8%. The grain refinement strengthening and the Orowan strengthening contribute to the most increment in strength of the hybrid modified composites, while the Si precipitation and some un-melted ZrO₂ nanoparticles inside the cells and the bimodal microstructure play a dominant role in increasing ductility.