Study On High Temperature Creep Performance Of New Mg-Al-Zn Magnesium Alloy

In general,the comprehensive mechanical properties of magnesium alloys are better,but when the temperature exceeds 120?,it will affect the application of magnesium alloy under some special conditions.Adding a small amount of elements such as Y,Sn,and Mn to the magnesium alloy can significantly improve the creep resistance of the alloy.At present,most researches on magnesium alloys are carried out under high temperature and high stress conditions,and research under high temperature and low stress conditions is quite rare.In order to better design the magnesium alloy with good creep resistance,this paper selected the magnesium alloy designed by the cooperative research group,which contains a small amount of multielement,extruded Mg-3Al-0.8Zn-0.4Mn-0.4Sn?AZMT30?sheet and pipealloy,extruded Mg-2.6Al-0.6Zn-0.5Mn-0.7Sn-0.01Y?AZMT31?sheet alloy.Through the tensile creep experiments,analysis of creep behavior of the alloy at the condition of200? to 300?,6-22 Mpa.The main research contents and conclusions are as follows:?1?The high temperature creep behavior of extruded AZMT30 sheet and pipe alloy and extruded AZMT31 alloy at 200?-300? and 6-22MPa were studied.The results show that with the increase of temperature and stress,the steady state creep rate of AZMT30 sheet and pipe alloy and AZMT31 sheet alloy increases continuously,and the total strain is correspondingly increased.The steady-state creep rate and the total strain incrementare more sensitive to temperature than the stress,that is,the temperature can affect the creep resistance of the three alloys more than the stress.Under the same conditions,AZMT30 pipe alloy has the lowest steady-state creep rate and total strain,and always shows the best creep resistance.?2?The phases and microstructures of three alloys before and after creep were analyzed by XRD,SEM and EDS.The results show that the extruded AZMT30 sheet and the pipe alloy are composed of?-Mg matrix and?-Mg₁₇Al₁₂2 second phase before and after creep;Extruded AZMT31 sheet alloy is composed of Mg,Mg₁₇Al₁₂2 and Al₈Mn₅ before and after creep;And with the increase of temperature,the Mg₁₇Al₁₂phase in the AZMT30 sheet and the pipe alloy increases,and the Mg₁₇Al₁₂2 and Al₈Mn₅ phases in the AZMT31 sheet alloy are also increased.?3?The stress index n and the creep activation energy Q of the three alloys were obtained by the constitutive equation,and the creep mechanism of the alloy was analyzed according to the calculation results.The results show that the average stress indexes of extruded AZMT30 sheet and pipe alloy and AZMT31 sheet alloy are 1.94,1.96 and 1.04,respectively.The average creep activation energies of the three alloys were 92.84 kJ/mol,71.36 kJ/mol and 84.53 kJ/mol,respectively.The creep mechanism of AZMT30 sheet alloy is the grain boundary slip mechanism.The AZMT30 pipe alloy is the grain boundary slip mechanism at low stress and becomes the dislocation slip mechanism under high stress.The creep mechanism of AZMT31sheet alloy is grain boundary diffusion mechanism.?4?The results of tensile test at room temperature and the microhardness test before and after creep show that the microhardness of the deformation of the three alloys after creep is higher than that of the undeformed and pre-creep alloy.The extrusion state AZMT30 sheet alloy has high microhardness before and after creep,and the tensile performance of AZMT31 sheet alloy at room temperature is relatively good.