Microstructure Evolution Of LPSO Phase And The Corresponding Mechanical Properties And Damping Capacities In Mg-RE-Zn Alloys

In recent years,the development of major equipment in key areas such as aerospace,rail transit,and national defense and military industry has become more rapid,lighter and more powerful,and vibration and noise problems have become increasingly prominent.The structural and functional integrated magnesium alloy with high-strength damping characteristics is of strategic significance for improving the reliability,stability,control accuracy and survivability of equipment.Therefore,the development of new structural and functional integrated magnesium alloys with high strength and high damping properties has become increasingly important.However,due to the contradiction between the strength and damping performance of magnesium alloys,it is difficult to achieve both,which severely restricts the development and application of high-strength damping magnesium alloys.The discovery of LPSO phase（long period stacking ordered phase）magnesium alloy provides a reference idea for the preparation of high-strength damping magnesium alloy.However,the current research on the damping mechanism of LPSO phase in Mg-RE-Zn alloy is still lacking.In response to the above problems,this article focuses on the major requirements for high-strength damping magnesium alloys in the upgrading of major equipment such as aerospace,rail transit,national defense and military industry.Mg-RE-Zn alloy is the research object to study the microstructure evolution law of LPSO phase in magnesium alloy and its influence on mechanical and damping properties.In this paper,firstly,the evolution of the LPSO phase in different states of the Mg-Er-Zn alloy which directly forms the LPSO phase in the as-cast state and its influence on the mechanical and damping properties are studied.Mg-Er-Zn series alloys with different amounts of LPSO phases were prepared by controlling the content of Er element in the magnesium alloy.The study found that after solid solution treatment of Mg-Er-Zn alloy,the second phase in the as-cast magnesium alloy disappears,and the alloying elements exist in the form of solid solution atoms.After solution treatment,the mechanical and damping properties of the magnesium alloy can be improved at the same time.After the Mg-Er-Zn alloys are extruded,a lamellar LPSO phase can be obtained.With the increase of the content of Er element,the number of lamellar LPSO phase gradually increases,but the damping performance of the alloy shows a downward trend,indicating that the lamellar LPSO The phase is not conducive to the improvement of the damping performance of magnesium alloys.Secondly,the microstructure evolution of Mg-Gd-Zn alloys forming LPSO phase after heat treatment with different components under different heat treatment processes and their effects on the mechanical and damping properties of magnesium alloys are studied.By fixing the ratio of Gd/Zn atoms,the change of the content of LPSO phase in the magnesium alloy is regulated.The study found that after the solution treatment,the Mg-Gd-Zn alloy still has only two second phases:α-Mg matrix phase and（Mg,Zn）₃Gd eutectic phase.The strength of Mg-Gd-Zn alloy has no obvious change,but the plasticity of magnesium alloy has increased to varying degrees.The tensile strength of Mg_97.67Gd_1.33Zn₁ alloy is 260MPa,the elongation after fracture is 26%,and the damping value is 0.0128,with good comprehensive performance and excellent plasticity.Then,based on the experimental results of the first two chapters,the evolution of the LPSO phase and the influence on the mechanical and damping properties of the Mg-Gd-Y-Zn-Mn alloy containing the Mg-Y-Zn type LPSO phase and the Mg-Gd-Zn type LPSO phase were studied.By changing the Gd element content,heat treatment and deformation process control,the quantity,morphology and distribution of the LPSO phase of the Mg-Gd-Y-Zn-Mn alloy with two LPSO phases are adjusted,and its influence on the mechanical and damping properties is studied.The study found that the heat treatment process has a greater impact on the damping performance of the Mg-Gd-Y-Zn-Mn alloy.The maximum damping obtained under different heat treatment processes is 0.014 and the minimum is 0.005.The difference between the two is nearly 3 times,which is comparable to that of LPSO.The morphology is closely related.Therefore,the morphology control criteria for LPSO phase high-strength damping magnesium alloys are proposed.If high-damping magnesium alloys are to be designed,more rod-shaped LPSO phases should be obtained as much as possible,and lamellar LPSO should be obtained if the tensile strength is to be improved.Subsequently,the influence of Nd,which is not involved in the formation of LPSO phase,on the microstructure evolution and mechanical and damping properties of Mg-Gd-Y-Zn-Mn alloy was studied.The study found that adding a small amount of Nd to the Mg-Gd-Y-Zn-Mn alloy further optimizes the mechanical and damping properties of the magnesium alloy,and the presence of Nd can hinder the transition from the eutectic phase to the LPSO phase.Among them,the magnesium alloy with 1.0wt.%Nd element has better comprehensive mechanical properties,the tensile strength reaches 414MPa,the elongation after fracture is 7.3%,and the damping value is 0.015.Finally,the mechanism of balance optimization between mechanical and damping properties of Mg-Gd-Y-Zn-Mn alloy is discussed.The study found that LPSO phase extruded magnesium alloy can obtain interphase grains by preparing bimodal structure.This kind of structure can not only cooperate with the stress deformation of magnesium alloy,improve the strength and plasticity of magnesium alloy,and it is also very beneficial to the improvement of the damping performance of magnesium alloy.For the extruded Mg-Gd-Y-Zn-Mn alloy,the kink microstructure is summarized.