Study On Thermal Deformation Characteristics And Microstructure And Properties Of Mg-3Sn-1Mn-1La Magnesium Alloy

As one of the lightest metal structural materials,magnesium alloy has broad market application prospects.However,when the temperature is increased,its strength will be greatly reduced and cannot be used as a key material in a higher temperature environment.The development of heat-resistant magnesium alloy is of great significance to expand the application of magnesium alloy.Studies have shown that the addition of Sn as an alloying element to magnesium can form the Mg₂Sn phase,which is a heat-resistant strengthening phase with good thermal stability?melting point 778??and high hardness value?119HV?.As a result,Mg-Sn alloys have become a potential heat-resistant magnesium alloys series.In order to reveal the flow stress change and microstructure evolution of Mg-3Sn-1Mn-1La alloy during hot deformation,the hot deformation behavior of Mg-3Sn-1Mn-1La alloy was investigated.In this dissertation,the hot compression experiment were performed on the Gleeble-3800 thermal simulator in the deformation temperature range of 200-450?,the strain rate range of 0.001-1s^-1and the amount of compression of 50%.The effects of friction and deformation temperature rise on the flow stress were analyzed and corrected.The characteristics of the stress-strain curve of the alloy were analyzed.After friction and temperature correction,the peak stress constitutive model,strain-corrected flow stress constitutive model and dynamic material model processing map of the alloy were established.Through the optical microscope?OM?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,and electron backscatter diffraction?EBSD?and other analytical methods to study the influence of deformation parameters on microstructure evolution and deformation mechanism.The main results are as follows:?1?Through stress-strain curve analysis,it was found that the flow stress decreases with the increase of the deformation temperature or the decrease of the strain rate.Due to the work hardening effect,the flow stress increases rapidly at beginning.Subsequently,due to the dynamic softening effect of such as dynamic recovery and dynamic recrystallization,the increase rate of the flow stress slows down and gradually decreases after reaching the peak,and eventually stabilizes.?2?The friction between the testing machine and the sample will make the flow stress higher than the true value,and the deformation heat generated during the deformation process will make the flow stress lower than the true value.The effect of the friction and temperature raise on flow stress was corrected.The influence of the friction and temperature raise on the flow stress increases with the decrease of the deformation temperature or the increase of the strain rate.The influence of friction on the flow stress is not that much.?3?Using the corrected flow stress data,the peak stress and strain-corrected constitutive equation were established.The reliability of the strain-corrected constitutive equation was assessed.The results suggest that the developed constitutive equations can adequately describe the relationships between the flow stress and deformation parameters.?4?The microstructure evolution of Mg-3Sn-1Mn-1La alloy during hot compression was analyzed.The deformation temperature and strain rate both have significant impacts on the evolution of microstructure.As the deformation temperature increases or the strain rate decreases,the degree of recrystallization and the size of recrystallized grains gradually increase.?5?Using the corrected stress-strain data,the processing map of Mg-3Sn-1Mn-1La alloy was established,and the microstructure analysis of different processing areas was carried out.The most suitable hot working conditions of the alloy are at the temperature range 400-450?and at the strain rate range 0.1-1s^-1.