Effects Of Ga On Microstructure,mechanical Properties And Damping Capacity Of Mg-6Zn-0.6Zr Magnesium Alloy

ZK60（Mg-6Zn-0.6Zr）magnesium alloy has the advantages of being lightweight and high strength,but it also has some problems,such as serious hot cracking tendency,poor plasticity,and poor damping performance.Alloying is one of the main methods to improve its mechanical properties.Because of the excellent plasticity and damping capacity of Mg-xGa binary alloys,Ga is proposed to be used as an alloying element in this study to clarify its effects on the microstructure,mechanical properties,and damping capacity of ZK60 magnesium alloys and explore its mechanism.The purpose is to provide new attempt of adding Ga element into Mg-Zn-Zr alloys and provide powerful composition design experience for the development of Mg-Zn-Zr alloys with high strength,high plasticity and high damping.At first,the effects of Ga alloying on the microstructure characteristics of as-cast and as-solutionized Mg-6Zn-0.6Zr alloys were studied,and the mechanism was explored.The experimental results show that Ga mainly exists in three forms in the as-cast Mg-6Zn-0.6Zr-xGa alloys,which are in the form of solid solution atoms,enriched in the Mg₇Zn₃ phase and combined withα-Zr to form GaZr₂ phase.The addition of Ga consumes Zr element due to the interaction between solute atoms which comes from Ga alloying,thus weakening the grain refinement of Zr,resulting in the coarser grain size of as-cast and as-solutionized alloys.In addition,the interaction between solute atoms also leads to the increase of the eutectic Mg₇Zn₃ phase in the as-cast alloys,and also improves the thermal stability of the eutectic Mg-Zn phase.The interaction between the Ga atom and Zn atom inhibits the dissolution of the Mg₇Zn₃ phase enriched with Ga during the homogenization process and becomes the residual second phase in theα-Mg matrix.The alloy sheets are prepared of as-solutionized Mg-6Zn-0.6Zr-xGa alloys by high strain rate rolling deformation at 300℃,and the effects of Ga content on the dynamic recrystallization（DRX）behavior of the alloys were clarified.The experimental results show that there are obvious differences in the dynamic recrystallization behavior of the alloys with different Ga content during high strain rate deformation.Adding 0.5 wt.%Ga is beneficial to DRX,and the volume fraction of DRX increases from 89%of the Mg-6Zn-0.6Zr alloy to 94%of Mg-6Zn-0.6Zr-0.5Ga alloy;When the Ga content increases,the dynamic recrystallization behavior of the alloys is inhibited,and the volume fraction of DRX decreases gradually.The mechanism of Ga content affecting DRX behavior is related to the effect of Ga alloying on the stacking fault energy（SFE）.The interaction between Ga atom and Zn atom weakens the effect of Ga on reducing the SFE of Mg alloys,which affects the twin induced recrystallization（TDRX）behavior during high strain rate deformation.Therefore,the DRX behavior is inhibited in the alloys containing high Ga content.The residual Ga-riched second phase initiates the PSN mechanism of DRX.The effects of Ga content on the mechanical properties of as-HSRRed Mg-6Zn-0.6Zr-xGa alloy sheets were studied,and its mechanism was analyzed.The experimental results show that the addition of Ga leads to the reduction of the strength and plasticity of ZK60 alloys.The ultimate tensile strength of the Mg-6Zn-0.6Zr alloy sheet is 361 MPa,the yield tensile strength is 267 MPa,and the elongation after fracture is as high up to 25.3%.However,the strength and plasticity of the alloys gradually decrease with the increase of Ga content.It can also be ascribed to the increasing grain size and the decreasing number of dynamic precipitates with the addition of Ga content.The existence of Ga atoms affects the dynamic precipitation behavior of Mg-6Zn-6Zr alloy.When analyzing the tensile deformation behavior of the alloys,it is found that the work hardening ability of Mg-6Zn-0.6Zr-xGa alloy sheet in the early stage of uniform plastic deformation can be significantly improved with the increase of Ga content during the tension process in room temperature.However,in the later stage of uniform plastic deformation,the work hardening curve of the alloys fluctuates periodically,which eventually indicates the fracture failure of the material,and this phenomenon becomes more and more obvious with the increase of Ga content.Due to the decreasing degree of the alloys caused by the Ga addition and the formation of the coarse undissolved second phase,the deformation behavior of the alloy sheet is uneven.And it is easy to produce stress concentration during tensile deformation,thus resulting in fracture failure.The effects of Ga content on the damping capacity of the as-cast,as-solutionized,and as-HSRRed Mg-6Zn-0.6Zr-xGa alloys were studied,and the mechanism was explored.The experimental results show that the damping mechanism of the alloys in three conditions is all dislocation damping.The number of solute atoms in theα-Mg matrix increases with the increase of Ga content,thus increasing the number of weak pinning points on the dislocation lines,which makes the critical strain amplitude(ε_Cr)of the alloy increase gradually.The second phase in the as-cast alloys acts as the strong pinning point of dislocation,thus hindering the mobility of the dislocation lines.A minor addition of Ga content is beneficial to improve the damping capacity of the as-cast alloys,but the effect of the second phase relative damping capacity gradually changes from promotion to hindrance with the increase of Ga content.The damping capacity of as-solutionized Mg-6Zn-0.6Zr-xGa alloys is mainly affected by the lattice distortion,grain size,and the undissolved particles.When 0.5 wt.%Ga is added,the damping capacity is not good due to the small dislocation density in the alloy and the large lattice distortion.With the increase of Ga content and the strain amplitude,the damping capacity of the alloys is significantly improved.Especially the damping value Q^-1 reaches 0.022 in the Mg-6Zn-0.6Zr-1.5Ga alloy.The damping mechanism of the as-HSRRed Mg-6Zn-0.6Zr-xGa alloys is related to the strain amplitude.When the strain amplitude is lower than 0.065%,the dislocation damping mechanism plays a major role.At this time,Ga alloying will significantly hinder the mobility of dislocation lines,which is adverse to the damping capacity.When the strain amplitude exceeds 0.065%,the damping mechanism of the alloys is micro-plastic damping.At this time,the influence of dislocation proliferation should be considered.Ga alloying is conducive to the improvement of the micro-plastic damping capacity of the Mg-6Zn-0.6Zr-xGa alloys.