Achieving highly dense metal injection moulding 6061 Al with superior strength-ductility

Metal injection moulding (MIM) has been widely used in manufacturing components of iron-base alloys, stainless steels, and copper and titanium alloys, due to its advantages in fabricating small parts in high quantities and of complex shape. However, the application of MIM for aluminum alloys is severely limited by their insufficient densification and mechanical properties, caused by defects left after sintering due to the oxide layer on the surface of aluminum powders. Here, we introduce an oxalic acid catalytic degreasing process, which effectively overcomes the adverse effects of the oxide layer and enables the fabrication of highly dense MIM 6061 aluminum alloys (with a density of 99.5 % of theoretical). Besides, the SiO₂ formed during the degreasing process serves as a reactive precursor, transforming the otherwise traditionally detrimental oxide layer into a beneficial reactant that facilitates the formation of a nano-MgAl₂O₄ quasi-network heterostructure. Remarkably, the heat-treated MIM 6061 aluminum alloy exhibits an excellent strength-ductility synergy of a yield strength 317.4 ± 9.2 MPa, an ultimate tensile strength 366.8 ± 8.3 MPa and an elongation 11.6 ± 0.2 %, comparable to those of heat-treated wrought and additively manufactured 6061 aluminum alloys. High density together with the formation of the heterogeneous structure offers high performance and opens up new opportunities for wide industrial application of MIM aluminum alloys.