Nitrogen-induced interfacial engineering in Al/alumina hollow sphere (AHS) syntactic composites for extreme specific energy absorption

Abstract

Lightweight and high-performance aluminum matrix syntactic composites (AMSCs) with a low density (<2.2 g/cm3) were developed through a nitrogen-induced self-forming process. This exothermic nitridation reaction enables pressure-free fabrication, thereby minimizing damage to incorporated alumina hollow spheres (AHS) during processing. Simultaneously, the process facilitates the in-situ formation of an aluminum nitride (AlN)-rich interfacial layer, affording enhanced interfacial characteristics. The resulting interface promotes efficient load transfer, activates Orowan-type strengthening, and restricts local deformation, contributing to significant improvements in the compressive strength and energy absorption capacity of the composites. The mechanical properties of the composites reinforced with 20–60 vol% micro-sized alumina hollow spheres were significantly improved. Notably, the plateau stress of A6061/40%AHS and A356/40%AHS increased by 46.7% and 56.2%, respectively, and the energy absorption increased by 42.2% and 57.4% compared to that of traditional Al/40%AHS AMSCs. Impressively, the compressive strength, plateau stress, and energy absorption of A356/40%AHS reached 292.6 MPa, 229 MPa, and 115 MJ/m3, respectively, underscoring its potential for application in advanced energy-absorbing structures. A modified Gibson–Ashby framework was employed to clarify these enhancements, emphasizing the role of the AlN interface in increasing the effective density ratio and structural efficiency. This study emphasizes the critical importance of interfacial engineering in surpassing classical scaling predictions and provides a pathway to next-generation, lightweight energy-absorbing materials.