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The Research Of Mg-Mn-Zn Series Magnesium Alloy On The Structure And Properties

Posted on:2018-11-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:L LaiFull Text:PDF
GTID:1311330515961381Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
Mg-Mn Magnesium alloy is a kind of non-heat treatable alloy with coarse as-cast grain size.Due to the poor plastic deformation ability,it is hard to obtain uniform deformation structure and easy to crack.Improving the ability of plastic deformation of magnesium alloy and developing anew type of wrought magnesium alloy with high plasticity has become one of the most important issues in the research of magnesium alloys.With Mg-Mn alloy and Mg-Mn-Zn alloy as the research object,by first principle calculation method,explains the Mn in magnesium solid solution strengthening effect in principle;The microstructure of the alloy was observed by means of optical microscope,scanning electron microscope,transmission electron microscope and X ray diffraction analysis;The mechanical properties,corrosion resistance and damping properties of the alloys were evaluated by means of tensile tests at room temperature,electrochemical tests and mechanical dynamic analysis;The constitutive equations of as cast and extruded alloys were constructed by hot compression experiments;The mechanical properties and thermal processing properties of Mg-Mn-Zn wrought magnesium alloy were evaluated by comparing the AZ40 magnesium alloy with the similiar content of alloy elements.In the melting process of different preparation of Mg-Mn alloy,found by the microstructure difference between Mg-Mn master alloy,Mn flux and three Mn anhydrous manganese chloride added Mg-Mn alloy prepared in the form of the very small,there are a larger size of-Mn particles.The TTT curve of Mg-Mn alloy was drawn by means of conductivity measurement.That of cast Mg-Mn alloy,Mn magnesium alloy elements in maximum solid solubility only in the melting and solidification process obtained,heat treatment at 250 ℃ to will lead Mn in matrix precipitation.The first principles calculation of Mg-Mn solid solution shows that Mg2s and 2p orbital electrons have strong hybridization with Mn3d orbital electrons,and Mg-Mn forms a strong covalent bond.In addition,Mn solid solution to Mg will also make the Mg-Mg covalent bond around the Mn atoms to a certain extent,so that the Mn atom has a high solid sollution strengthening efficiency.The addition of Zn has a significant effect on the microstructure and properties of extruded Mg-Mn alloy.The dynamic recrystalization of extruded Mg-Mn-Zn alloy increases with the increase of Zn content,and the microstructure is more uniform.The strength and elongation of the alloy increased with the increase of Zn.The effect of adding 0.5%Zn on the mechanical properties of the alloy was improved obviously.The addition of Zn could improve the performance of the alloy but the effect was weakened.In the process of Mg-Mn-Zn alloy,a small amount of disk like alpha-Mn phase is dispersed,and the dispersion of the alloy is within 20nm There is a {0001} texture of extruded alloy,the basal texture with Zn elements added there is a tendency of weakening.At the same time,{0001}texture was diffused in the TD direction,with the increase of Zn content,increase the degree of texture.With the increase of annealing temperature and Zn content,the recrystallization nucleation time is shortened,and the recrystallization rate of Mg-Mn-Zn magnesium alloy can be improved and the recrystallization of Mg-Mn-Zn alloy can be improved.The hot deformation behavior of Mg-2Mn-Zn magnesium alloy was studied by isothermal compression test,and the rheological behavior of Mg-2Mn-Zn alloy during isothermal compression deformation was studied,The material constants of the alloy during hot deformation were obtained:Deformation activation energy Q=223.863kJ/mol,Stress index n=4.87856,Average stress factor a=0.022503.The thermal deformation of Mg-2Mn-Zn alloy is slightly worse than that of AZ40 alloy.The high plasticity magnesium alloy with uniform size of1.83m was obtained by ECAP.The extruded Mg-2Mn-Zn alloy with 1 passes of ECAP deformation,deformation of alloy tensile strength decreased from 251 MPa to 300MPa,the yield strength decreased from 251MPato 133MPa,but the elongation rate increased from 12.1%to 26.7%,mainly due to the grain refinement of magnesium alloy and the grain boundaries of high plastic compatibility stress activation the nonbasal slip.Considering that the addition of alloying elements is less,and the proper amount of Mn element can improve the corrosion resistance of magnesium alloy,the corrosion resistance of Mg-Mn-Zn alloy is further studied.The corrosion of Mg-Mn-Zn alloy in the extrusion process of the alloy corrosion,the increase of Zn content will lead to the increase of pitting corrosion.The presence of grain boundary can accelerate the corrosion rate,and the corrosion resistance of the alloy with high degree of recrystallization is poor.To improve the corrosion resistance of alloy can be a Zn element,but when the Zn content exceeds 0.5%,the corrosion resistance of the alloy is decreased significantly,in five kinds of alloy in Mg-2Mn-0.5Zn alloy had the best corrosion resistance.The effects of Zn content,cold deformation and heat treatment on the damping properties of as extruded Mg-Mn-Zn alloy were investigated.It was found that the strain independent damping of extruded Mg-Mn-Zn alloy decreased with the increase of Zn element.The addition of 2%Zn can suppress the damping peak near the alloy’s temperature of about 200 ℃,but the damping peak caused by the grain boundary sliding at the temperature of about 350 ℃ is obvious.The cold deformation can lead to the decrease of the damping property of the extruded Mg-Mn-Zn alloy at room temperature,and the lower the pressure,the lower the damping value of the alloy.The annealing treatment results in the decrease of the room temperature damping,which is mainly due to the decrease of the dislocation density and the precipitation of alpha-Mn phase.
Keywords/Search Tags:Mg-Mn-Zn alloy, microstructure, mechanical property, corrosion property, damping property
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