Study On Magnesium Matrix Materials With Multi-internal Friction Mechanism

Pure magnesium and its alloys are good vibration and noise reduction materials due to their high damping capacities.In order to explore the effects of various internal friction mechanisms on the damping capacity of pure magnesium and magnesium alloys,other damping mechanisms different from the dislocation damping mechanism are introduced by tensile deformation,ultrasonic impact,heat treatment and addition of graphite particle.The microstructure and properties of pure magnesium and magnesium alloys were analyzed by OM,SEM,TEM and related performance tests.The correlation between damping and strain amplitude of pure magnesium and magnesium alloys was studied in detail,and the internal friction peaks were investigated.The research results are as follows:（1）The damping mechanism of the twin boundary is introduced into the pure magnesium by tensile deformation.As the amount of deformation increases,the number of twins also increases.Compared with pure magnesium,the damping capacity of pure magnesium is improved after tensile deformation.With the increase of the amount of tensile deformation,the damping value of pure magnesium shows a trend of increasing first and then decreasing,and the value of critical strain amplitude increases.（2）The damping capacity of pure magnesium is improved by ultrasonic impact on pure magnesium.The impact time and the impact current have a great influence on the damping capacity of pure magnesium.With the increase of the ultrasonic impact time and the current,the damping capacity of pure magnesium decreases.（3）In the strain amplitude-independent stage,the damping value of the alloy also increases with the increase of aging time.Compared with the as-cast Mg97Zn1Y2 alloy,the strain amplitude-dependent damping of the heat-treated alloy decreases,and as the aging time increases,the strain amplitude-dependent damping value of the alloy decreases.The critical strain amplitude of the alloy is higher than that of the as-cast alloy after heat treatment.The damping mechanism of the heat treated Mg97Zn1Y2 alloy mainly includes dislocation damping,grain boundary and phase boundary damping.（4）The addition of graphite particle has little effect on the microstructure of the matrix.Compared with the as-cast Mg97Zn1Y2 alloy,the hardness of the graphite particles/Mg97Zn1Y2 composite is low.The smaller the size of the graphite particles,the lower the volume fraction,and the higher the hardness value of the graphite particles/Mg97Zn1Y2 composite.The damping capacities of graphite particles/Mg97Zn1Y2composites are higher than those of Mg97Zn1Y2 alloys in the strain-independent stage.As the graphite particle size decreases and the volume fraction increases,the damping capacity of the graphite particle/Mg97Zn1Y2 composite is better.In addition to the dislocation damping mechanism,there are also interface damping and grain boundary damping.（5）The correlation between damping and strain amplitude of pure magnesium and magnesium alloys is analyzed from hysteresis and microplastic deformation,respectively.When the strain amplitude is lower thanε_cr2,the relationship between the damping properties of pure magnesium and the strain amplitude in the hysteretic stage can be explained by the G-L dislocation pinning model.When the strain amplitude is higher thanε_cr2,pure magnesium is in a state of microplastic deformation.During the aging treatment of Mg97Zn1Y2 alloy,theε_cr1r1 value increases with the increase of aging time,while the values of C₁ and C₂ decrease.When the strain amplitude is higher thanε_cr3,the accumulation and entanglement of dislocations leads to a decrease in the number of movable dislocations inside the grains,which reduces the activation volume of dislocation slip.（6）There are three internal friction peaks in pure magnesium,and only two obvious internal friction peaks existed in pure magnesium after tensile deformation and ultrasonic impact.The internal friction peak of P₁ is related to the interaction of dislocations with vacancies and solute atoms in pure magnesium;The internal friction peak of P₂ is related to the movement of dislocations in pure magnesium,and P₃ peak is the grain boundaries internal friction peak.