Influence Of Rolling On Microstructure And Properties Of AZ31 Magnesium Alloy Sheets Processed By Continuous Extrusion

As the lightest constructional material,magnesium alloy has high specific strength,high specific stiffness,good magnetic-shielding ability,good damping ability,and good machinability,which is considered as "the green engineering material of the 21st century".So it has been successfully applied in many fields such as aviation,spaceflight,communication,telecom,health,as well as machine manufacturing and traffic.But magnesium alloy has a hexagonal close-packed(hcp)crystal structure,so it is normally low formability at the room temperature.Weight reducing is the major trend,thus magnesium alloy will has a very good marketing prospect.At present,the production process of magnesium alloy plates mainly include ingot extrusion rolling process,double roll rolling process and ingot hot rolling process.All the above processes have defects such as complicated process,high production cost and unstable process.Continuous extrusion process produces heat by friction which realized continuous production of feeding at room temperature.It has the advantages of low production cost,high production efficiency and continuously production.At present,most AZ31 magnesium alloy plates produced by continuous extrusion are medium and thick ones,but the actual application of magnesium plate is mainly thin sheets.Rolling is the most effective way to obtain magnesium alloy thin sheets.In this paper,AZ31 magnesium alloy sheets prepared by continuous extrusion were thinned by hot rolling and warm rolling.In order to refine the crystal particle size and improve the formability of AZ31 magnesium alloy sheets.It has directive significance to the preparation and reprocessing of continuous extrusion magnesium alloys sheets.In this paper,AZ31 magnesium alloy plate was processed by unidirectional hot rolling,expanding hot rolling and warm rolling.The experimental methods such as metallographic microstructure observation,X-ray diffraction(XRD),tensile test,Erichsen test and forming limit test were used to study the microstructure evolution and mechanical properties of magnesium alloy sheet during the rolling.As the result,the mechanical properties of magnesium alloys sheets was improved with the increase of rolling pass.The grain size of hot rolled sheets was reduced from 31.3 ?m to 9 ?m.After annealling,the average grain size of hot rolling sheet was 7.4 ?m,the tensile strength was 261.88MPa,and the elongation was 27%.After seven passes of rolling,when the total reduction rate reached 80%the grain size of the middle area and the edge area was basically the same,and the microstructure of the plate was well homogenized.After 230? warm rolling the significant grain size of sheet was 6.8?m.The average grain size of sheet was 5.8 ?m,tensile strength was 267.75MPa and elongation was 21.66%after annealing.Rolling can effectively weaken the density of the(0002)base surface texture which reduced from 32.35 to 11.78,but it was increased with rolling pass.The polar density of(0002)base surface texture of sheets can be reduced more effectively by expanding hot rolling which could be reduced to 8.39.The rolled magnesium alloy sheet has good forming properties.The erichsen value can reach 13.1 mm at 250?,and the forming limit diagrams(FLD,Forming limit diagrams)of AZ31 hot rolled sheet were obtained through the forming limit test.The FLD of AZ31 magnesium alloy plate were obtained by simulation and theoretical derivation.