Simulation Study On The Effect Of Twin Boundaries On The Mechanical Behavior Of High-entropy Alloys

Magnesium（Mg）alloy,as a green engineering material in the 21st century,has become an important light alloy material due to its excellent advantages such as low density,high specific strength,and damping capacity.In recent years,magnesium alloys have been used in aerospace,transportation,electronic communications,and other industries.However,as a potential inventory of light alloys,magnesium alloys must face the reality that due to the hexagonal compact packing（HCP）structure of magnesium alloys,the number of active slip systems at room temperature is limited,resulting in poor plastic deformation ability of magnesium alloys,which limits their wide application in various fields.Therefore,finding effective measures to improve the plasticity of magnesium alloys has become an urgent problem to be solved.Traditionally,rare-earth（RE）alloying is usually used to prevent the<a>basal slip of Mg alloys and activate their potential<a>pyramidal,<a>prismatic and<c+a>pyramidal slips to obtain five independent slip systems,so as to improve the plasticity of Mg alloys.Although some achievements have been made in improving the plasticity of Mg alloys by alloying,it still cannot meet people’s requirement.Therefore,there is an urgent need for a new approach to improve the plastic deformation ability of magnesium alloys.Crystalline/amorphous（C/A）dual phase structure is a new design strategy for improving the mechanical properties of magnesium alloys.In this paper,the effect of the content of rare earth element yttrium（Y）on the deformation mechanism and mechanical behavior of C/A Mg/（Mg Cu）_100-xY_xdual phase magnesium alloy under tensile load was studied by molecular dynamics simulation.The main research content of this article is as follows:（1）The deformation mechanism and mechanical behavior of C/A Mg/（Mg Cu）_100-xY_xdual-phase magnesium alloy under tensile load were studied,and the effect of different content of Y element on the mechanical properties and deformation behavior of C/A Mg/（Mg Cu）_100-xY_xwas revealed.The results show that the stress drop of dual-phase magnesium alloy with different content of Y element appears sharply after the yield point.With the further increase of the content of Y element,the stress drop almost disappears during the plastic deformation of dual-phase magnesium alloy,and the nearly perfect plastic flow behavior appears.The results also show that the yield stress of dual-phase magnesium alloy decreases with the increase of Y element content.（2）The occurrence of amorphization in the relaxation process of C/A Mg/（Mg Cu）_100-xY_xdual-phase magnesium alloy was studied.The results show for the first time that the amorphous phase thickness of the alloy increases significantly after relaxation,which is mainly due to the existence of Y element in the amorphous phase.With the increase of Y element content,the thickness of amorphous phase increases.The results show that the diffusion of element Y from amorphous phase to amorphous interface（ACI）promotes the migration of ACI to crystalline phase（i.e.,the crystallization of crystalline phase）.The results further pointed out that the crystallization of magnesium alloy depends on two factors:one is that the amorphous phase contains a certain concentration of Y element,and the other is the existence of ACI.Temperature also plays a role in increasing the thickness of amorphous phase.With the increase of temperature,the amorphous phenomenon becomes more obvious.The results show that there is a critical thickness of amorphous phase in dual-phase magnesium alloy,that is,the critical content of Y element.By adjusting the strength of amorphous phase or crystalline phase and optimizing the content of Y element（i.e.the thickness of amorphous phase）,the strength of dual-phase magnesium alloy can be improved while maintaining its excellent plasticity.