In-situ synthesis of Mg-based bulk metallic glass matrix composites with primary α-Mg phases

Highlights: ●Our study presents in-situ synthesis and mechanical properties of Mg-based BMGMCs. ●Mg-rich MgCuZnGd alloys with α-Mg 2nd phases are successfully designed via CALPHAD. ●An in-situ Mg-based BMGMC with 2 mm diameter is prepared in Mg₇₇Cu₁₂Zn₅Gd₆ alloy. ●α-Mg phases in BMG improve the plasticity due to formation of multiple shear bands. ●Mg-rich BMGMCs in this study are promising for lightweight structural applications. -- Abstract: Herein, we systematically investigate the in-situ synthesis and mechanical properties of Mg-based bulk metallic glass matrix composites (BMGMCs). From a well-known Mg₆₅Cu₂₅Gd₁₀ bulk glass former, a series of Mg_65+xCu_20–2x/3Zn₅Gd_10−x/3 (x = 0–18 at%) alloys are systematically designed and Mg-rich (>77 at% Mg) glassy/crystalline matrix composites containing primary α-Mg phases are successfully developed. Mg₇₇Cu₁₂Zn₅Gd₆ BMGMC (x = 12 at%) exhibits over two times higher compressive fracture strength (773 ± 20.6 MPa) and specific strength (2.6 × 10⁵ N m kg⁻¹) than commercial Mg alloys such as AZ31 or AZ91. In particular, compared with monolithic Mg-based BMGs, the BMGMC displays obvious yielding, serrated plastic flow and plastic strain of 0.22 ± 0.02%. This result is attributed to the dispersed primary α-Mg phases which prevent the rapid propagation of shear bands and promote the formation of multiple shear bands. The Mg-rich crystalline matrix composites (x = 14-18 at%) containing primary α-Mg phases exhibit an enhancement in the plastic strain (from 0% to 1.51%) and pronounced work hardening at the expense of yield strength ( < 500 MPa) due to the absence of the amorphous phase. These results would give us a promising strategy to fabricate Mg-based BMGMCs with high specific strength and enhanced plasticity for lightweight structural applications.