Molecular dynamics study of temperature-dependent Hall-Petch relation and temperature-induced softening behavior of nanocrystalline AlMg alloys

ZH Yu and HY Wang and LG Sun and ZH Li and LL Zhu, ACTA MECHANICA, 236, 5417-5433 (2025).

DOI: 10.1007/s00707-025-04442-2

The mechanical properties of nanocrystalline AlMg alloys with varying grain sizes (10-40 nm) across a temperature range of 300 K to 700 K are systematically investigated by using the molecular dynamics simulation, exploring the influence of temperature and grain size on the mechanical performance and deformation mechanisms of polycrystalline AlMg alloys. The simulation results reveal that as temperature increases, the elastic modulus and flow stress of the material gradually decrease, with mechanical properties deteriorating sharply at high temperatures (700 K and above), which is attributed to the significant reduction in dislocation density caused by crystal amorphization. Moreover, there exists the temperature-dependent transition between the Hall-Petch relationship and the inverse Hall-Petch relationship. At room temperature, the Hall-Petch relationship is observed when grain sizes exceed 25 nm, with flow stress increasing as grain size decreases, whereas at high temperatures, smaller grains exhibit inverse Hall-Petch behavior due to grain boundary sliding replacing dislocation sliding, resulting in enhanced flow stress with increasing grain size. Further analysis indicates that at high temperatures, the thickening of grain boundaries reduces their pinning capability on dislocations, while changes in the volume fraction of the crystalline phase directly affect dislocation generation capacity, thereby significantly influencing the material's flow stress. This research provides the theoretical support for understanding the mechanical behavior of nanocrystalline AlMg alloys under different temperatures and grain sizes and offers crucial insights for optimizing their high-temperature applications in the aerospace field.

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