Study On Mechanical And Damping Properties Of Magnesium-based Damping Composites With Multiple Internal Friction Sources

Multiple internal friction magnesium-based damping composites have become a research focus in the field of magnesium alloys in recent years,due to their high mechanical properties,high damping properties,small density,high specific strength,good heat dissipation performance and other excellent performances.Magnesium-based composite refers to a kind of metal composite prepared by adding a ceramic reinforcing phase or an intermediate compound to magnesium or magnesium alloy,which can complement the advantages and disadvantages of the materials and expand the further application fields and the range of use.Particle reinforcement has become the most concerned preparation method for magnesium-based composite because of its simple preparation process,low cost,and easy control.Among different kinds of ceramic particles,Si C particles have the characteristics of high melting point,stable chemical properties,and the same crystal structure as magnesium,which is very suitable as reinforcement for reinforcing magnesium-based composites.Based on this,in this article,Mg-Zn-Y alloy containing long-period special structure phase（LPSO phase）and quasicrystalline phase（I-phase）is selected as the magnesium matrix,while Si C ceramic particles is used as the reinforcement,and magnesium based composite with multiple internal friction sources is prepared by the stirring casting method.To study the effects of secondary phase and Si C on the mechanical properties and damping properties,OM,SEM,TEM,XRD,and DMA were applied and then we discussed the strengthening mechanism and damping mechanism.The findings are as follows:（1）Through the study of Si C/Mg97Zn1Y2 composite,it is found that with the increase of Si C content,the mechanical properties show an upward trend and then a downward trend.When the amount of Si C particles is 0.5wt.%,the mechanical properties are the best.The maximum compressive strength is 319 MPa,where there is an increase of 6.3%over the as-cast alloy.According to the fracture analysis,it can be seen that the composite belongs to the brittle fracture like the as-cast alloy,and the crack source extends from the edge of the sample to the inside.For the damping properties of the composite,when the strain amplitude is low,with the content of Si C increases,the damping properties of the composite increases.The addition of Si C at 0.5wt.%shows the best damping properties.At higher amplitudes,the damping characteristics do not change much.（2）Through the study of Si C/Mg94Zn5Y1 composite,it was found that the existence of Si C particles had little effect on the microstructure and quasicrystal phase of the as-cast alloy,and the distribution of Si C particles was relatively uniform.With the increase of Si C content,the mechanical properties increased first and then decreased,and the maximum compressive strength reached 350 MPa,where there was an increase of 13.8%compared with the as-cast based alloy.For the damping properties of this material,when the strain amplitude is low,the damping performance of the Si C/Mg94Zn5Y1 composite did not change much with the increase of the Si C content,but the critical strain amplitude value was smaller than that of the Mg94Zn5Y1 alloy,indicating that the dislocation of the composite was less affected by the weak pinning point,and the dislocation mobility was better,so the damping properties were better;when the strain amplitude was high,the damping properties of the composite were significantly better than that of the Mg94Zn5Y1 alloy.（3）Through the research on porous Mg97Zn1Y2 materials,it was found that the porosity increased with the increase of the content of foaming agent Mg CO₃.The increase in porosity reduced the density,which also reduced the mechanical properties of porous Mg97Zn1Y2materials.However,the damping property was greatly improved.When the strain amplitude is low,the damping properties increased with the increase of porosity.At high amplitude,the damping property was complicated by the presence of more interfacial damping because the composite was no longer dense.（4）Through the research on the damping-strain amplitude correlation of Si C/Mg97Zn1Y2,Si C/Mg94Zn5Y1 and porous Mg97Zn1Y2 materials,it was found that when the composite was in the stage of hysteresis,the₁ and₂ values of various composites were calculated by using G-L theory,which the number of strong and weak pinning points in each composite material was derived.When the composite was in the stage of microplastic deformation,the damping and strain amplitude were no longer linear,so it could not be explained by the G-L theory.We introduced a new dislocation damping theory to successfully solve the activation volume of dislocation slip and explain the influencing factors of damping properties.