The Study Of The Deformation Mechanism And Regulation Mechanism Of Dual-phase Nanostructured Mg Alloy

Magnesium(Mg)alloys,as the lightest metal material for industrial applications,possessing high specific strength and specific stiffness,excellent mechanical and physical properties,are ideal materials for defense high-tech fields.However,the hexagonal close-packed(HCP)crystal structure of Mg limits the number of independent slip systems for dislocation motion,making it poor in plastic deformation ability and low strength at room temperature,which is difficult to meet the requirements of structural parts.Therefore,the further development and application of Mg alloys in various fields are limited.Recent studies have shown that the plasticity of Mg alloys can be effectively improved by crystalline/amorphous dual-phase nanostructured Mg alloys.However,with the introduction of the amorphous phase,the strength of dual-phase nanostructured Mg alloys decreases.Thus,it is an important task to explore the strengthening mechanism of dual-phase nanostructured Mg alloys and to design and develop the dual-phase Mg alloys with excellent strength and plasticity.In this paper,the molecular dynamics simulation method is used to investigate the effects of stacking faults(SFs),the strength of amorphous phase and the crystalline phase on the mechanical properties and the plastic deformation mechanism of the dual-phase nanostructured Mg alloys under tensile load.Moreover,the strengthening mechanism of the dual-phase nanostructured Mg alloys is revealed.The main results and conclusions are as follows:(1)The effects of SFs and amorphous boundary(AB)spacing on the mechanical properties of dual-phase nanostructured Mg alloys are studied.The results show that with the increase of AB spacing,the plastic deformation mode of dual-phase nanostructured Mg alloys with large SFs spacing converts from the generation and growth of new grains in crystalline phase to the plastic deformation dominated by amorphous phase.When the AB spacing reaches a critical value,the plastic deformation of dual-phase nanostructured Mg alloys is completely provided by the amorphous phase,and the crystalline phase hardly participates in plastic deformation.However,the results also indicate that when the SFs spacing in the crystalline phase is relatively small,the crystalline phase still contributes to the plastic deformation of Mg alloys to a certain extent,even if the AB spacing reaches the critical value.These analyses shed light on that the introduction of SFs may promote the formation of new grains,and the deformation mechanism of dual-phase nanostructured Mg alloys is not only related to the AB spacing of amorphous phase,but also the SFs spacing of crystalline phase.(2)The effect of the strength of the amorphous phase and the crystalline phase on the mechanical properties and strengthening mechanism of the dual-phase nanostructured Mg alloys are investigated.The results confirm that the strength of dual-phase nanostructured Mg alloys can be significantly improved while maintaining its excellent plasticity by adjusting the strength of the amorphous phase or crystalline phase and optimizing the AB spacing.For the dual-phase nanostructured Mg alloys,when the amorphous phase(or crystalline phase)is strengthened to enhance its strength,the AB spacing shall be increased(or decreased)to obtain good plasticity at the same time.The results also indicate that the dual-phase nanostructured Mg alloy containing high strength amorphous phase exhibits three different deformation modes during plastic deformation with the increase of AB spacing:the capacity of the amorphous phase in the dual-phase nanostructured Mg alloys to accommodate plastic deformation is insufficient when the AB spacing is small,dislocations and new grains appear in the crystalline phase;with the increase of the AB spacing to 5.0 nm,the plastic deformation behavior of the dual-phase nanostructured Mg alloys is almost completely dependent on the amorphous phase;when the AB spacing further increases to 8.0 nm,due to the interaction and"pinned" of SBs to each other in the amorphous phase,the stress concentration is caused,so the new grain is still observed in the crystalline phase.However,compared with the dual-phase nanostructured Mg alloys with small AB spacing,the growth of new grain is very slow,and the plastic deformation of the dual-phase nanostructured Mg alloys is still mainly the amorphous phase.