Current-carrying friction-induced surface amorphization and abnormal grain growth in high-purity magnesium: A multi-field coupling mechanism

Achieving surface amorphization of high-purity magnesium (HP-Mg) without alloying additions remains challenging due to its high crystallographic symmetry and rapid atomic diffusivity. In this work, current-carrying friction was employed to modify the surface microstructure of HP-Mg under a constant load (20 N) and varying currents, utilizing a thermo-mechano-electrical multi-field coupling mechanism to refine grains and induce amorphization. Systematic characterization revealed that microstructural evolution under current-carrying friction diverges significantly from that under conventional mechanical friction. Specifically, an oxygen-rich amorphous/nanocrystalline hybrid layer​ formed at the interface, accompanied by a unique compositional diffusion transition zone. The introduction of current eliminated this transition zone, pinning oxygen atoms within the amorphous layer via electromigration, while Joule heating facilitated the amorphization process. This demonstrates that the current precisely regulates the amorphous/nanocrystalline ratio, interface morphology, and elemental distribution by controlling the competition and synergy between Joule heating and electromigration. Furthermore, the current induced localized abnormal grain growth (AGG) by lowering grain boundary migration barriers and weakening the Zener pinning effect. This study elucidates the coupled regulatory mechanism of mechanical action and electrical effects during current-carrying friction of Mg-based metals, providing a viable route for fabricating high-performance surface composite layers on high-purity magnesium without alloying.