Research On Phase Transformation Mechanism And Corrosion Resistance Of Mn-Cu-Al-Sn Damping Alloys

In recent years,the vibration controlling methods are very important for precision instruments in engineering manufacturing industry.High damping alloys,as functional materials,can reduce vibration and noise,thus improving the accuracy of sensors in mechanical equipment.Among the alloys,Mn-Cu based alloys exhibit an excellent damping capacity because of the motion of phase and twin boundaries.Experimentally,the specimens were prepared by induction-melting the pure metal.The influence of Sn content,plastic deformation and heat treatment process on the damping properties,mechanical properties and corrosion resistance of the alloy were emphatically analyzed,and this article takes Mn-（44-x）Cu-1.5Al-x Sn（x=0,1,2,3 wt.%）damping alloy as the research object.Subsequently,this article explored the influence of the Sn content on the damping and mechanical properties of the alloy,and with the increased of the Sn content,the FCT phase of Cu₄Mn Sn formed in the alloy,and the damping performance of the alloy gradually decreased.The best damping performance of the alloy was obtained at 1 wt%Sn content(Q^-1=0.06,when the torsional amplitude was 2×10^-4),and there were two main reasons for this.Firstly,the Sn element increased the martensite transition point and led to form more FCT phases and larger phase boundaries.Secondly,the addition of Sn reduced the activation energy of twin boundaries,which indicated the relaxation strength of the twins were obviously enhanced.In addition,because the large atomic radius of Sn elements and part of Sn atoms soluted into the matrix and enriched in grain boundaries,causing higher lattice distortion and more FCT phases,which made the FCT phases mainly distributed in the Sn-rich regions near grain boundaries.At the same time,the increasing of internal phase interface also made the plastic deformation more difficult.Moreover,Sn atoms and Cu₄Mn Sn particles played an important role in solid solution strengthening and second phase strengthening,respectively.Therefore,with the increasing of Sn-contenting,the hardness of the alloys increased continuously.Regarding the degradation behavior of Mn-Cu alloy damping performance,this paper also found that the addition of Sn element can effectively suppress the degradation of damping performance,and with increasing the Sn content,more pronounced inhibition.After 18 months of natural aging,with the Sn content from 0 to 3 wt.%,the internal friction decreased by 51.1%,22.99%,5.34%and 43.41%,respectively.The 2Sn alloy had the best degradation resistance.However,the damping performance of 3Sn alloy decreased due to the presence of Cu₄Mn Sn.Plastic deformation can improve the damping performance of Mn-43Cu-1.5Al-1Sn（wt.%）alloys,when the plastic deformation was 3%,the damping performance was the most superior(Q^-1=0.045167,when the torsional amplitude was 2×10^-4).The main reason was that a large amount of deformed martensite was produced during the plastic deformation of the alloys,and the dislocation caused by the deformation has a weak effect on the nailing of martensite phase.However,with the increase of plastic deformation,the nailing effect of internal dislocations played a dominant role,led to the rapid decline of damping performance.When the plastic deformation reached 30%,the martensite was almost completely nailed,and the damping performance hardly decreased with the increase of the plastic deformation.Moreover,when the amount of plastic deformation was below 5%,the hardness of the alloy increased faster,and the strengthening mechanism was mainly martensite phase boundary strengthening;when the amount of plastic deformation was above 5%,the hardness of the alloy increased slowly,and the strengthening mechanism was mainly dislocation strengthening.For the corrosion resistance of the alloy,this study first made its composition uniform through homogenization treatment to reduce the effect of galvanic corrosion.On this basis,it was found that the addition of the Sn elements made the alloy more prone to forming passivation film,reduced the self-corrosion current density of the alloy,and inhibited the pitting corrosion behavior of the alloy,which was mainly because the porosity of the passivation film of the alloy was the lowest(the porosity of the alloy was 2.28×10^-5 by calculation),and the passivation film had the best compactness.