Unlocking Exceptional Strengthening in Aluminum Alloys via Interstitial Cottrell Atmosphere Formation

ABSTRACT Developing low‐cost aluminum alloys with high specific strength is crucial for lightweight structural applications. Unlike carbon steels, fabricating aluminum‐carbon (Al‐C) alloys is challenging because the formation of incoherent carbide phases severely degrades ductility. In contrast, sputter‐deposited Al‐C thin films enable a uniform distribution of carbon interstitials, enhancing strength while preserving ductility. In this study, the governing deformation mechanism in Al‐C thin films is investigated through an analysis of the yield point phenomenon. Cyclic unloading‐aging‐reloading tensile tests combined with comprehensive microstructural characterization reveal that the formation of a Cottrell atmosphere dominates the deformation behavior. The study is further extended to assess whether Cottrell atmosphere‐induced strengthening persists with alternative solute atoms or alloyed aluminum matrices. Aluminum‐boron (Al‐B) and carbon‐doped 6061 aluminum alloy (6061AA‐C) thin films are examined as model systems. Both materials exhibit a pronounced yield point phenomenon accompanied by substantial strength enhancement. Notably, the 6061AA‐C films achieve an exceptional yield strength of approximately 715 MPa, surpassing that of conventional bulk aluminum alloys. These findings provide fundamental insights and suggest a new material design strategy for cost‐effective, high‐strength aluminum alloys incorporating light interstitial elements.