Abstract: Bulk nanocrystalline Mg₂Si(n-Mg₂Si) was prepared by mechanical milling and reactive hot-pressing in vacuum and its mechanical properties were characterized. The results indicate that the grain sizes of Mg and Si decrease non-monotonously with increasing ball-to-powder mass ratio(BPR). The content of Mg₂Si phase increases with increasing milling time; however, pure Mg₂Si phase cannot be obtained by direct ball milling. Moreover, monolithic is Mg₂Si phase can only be obtained when as much as 10% of excess Mg was blended in the raw mixtures. The relative density (D) and fracture toughness as well as hardness of bulk Mg₂Si samples can be raised effectively by increasing the pressure in hot-pressing. After hot-pressing at 400 ℃ for 60 min under 1.5 GPa, highly dense(D＞98%) n-Mg₂Si (d=60 nm) was obtained, whose fracture toughness (K_IC≈1.46 MPa•m^1/2) and Vickers hardness (HV≈ 4.38 Gpa) are superior to those of conventional coarse-grained Mg₂Si.

Key words: Mg₂Si; nanocrystalline; ball-milling; hot-pressing; mechanical properties