Circular manufacturing of Mg–eggshell composites: Transforming biogenic waste into functional reinforcements

Sustainable and frugal manufacturing approaches that reduce waste, energy use, and cost while enhancing resource efficiency are increasingly vital for next-generation materials development. In this study, a friction-based solid-state extrusion technique was employed to fabricate magnesium–eggshell composite rods using waste eggshells as a calcium carbonate CaCO 3 source. The combination of frictional heating, intense shear deformation, and mechanical mixing created a dynamic thermo-mechano-chemical environment that enabled homogeneous dispersion of the eggshell powders and induced extensive dynamic recrystallization in the Mg matrix. Transmission electron microscopy revealed nanoscale fragmentation of CaCO 3 particles and interfacial reactions forming CaO and MgO, confirming in-situ decomposition and reaction-driven bonding between the reinforcement and matrix. The refined grain structure and in-situ oxide formation together contribute to enhanced interfacial integrity and microstructural stability. This work demonstrates a scalable and energy-efficient pathway to produce Mg-based metal–matrix composites by reusing biogenic waste, aligning sustainable processing with advanced alloy design.