Effect Of Mn Addition On The Microstructure And Properties Of Mg-5Sn-2Al-Zn Alloys

Mg-5Sn-2Al-Zn-xMn(x=0,0.2,0.5and0.8)alloys with different compositions were made by using pure Mg,Sn,Al,Zn and Mg-10%Mn alloy under laboratory conditions..Because the crystallization process of the alloy in the casting is very fast,so it is difficult to get balanced organizations.This resulted in a serious segregation of components in organizations of alloys.In order to balance the organization,uniform compositions,and prepare for subsequent plastic deformation experiment,alloys need to be carried on heat treatment.Analyze alloy microstructure of different Mn contents by means of X-ray diffraction(XRD),optical microscopy,scanning electron microscopy(SEM)with energy dispersive spectrometer(EDS)and transmission electron microscope(TEM).Then test mechanical properties of alloys by using compression intensity tester and hardness tester.By the above method,we analyze effect of Mn in TAZ521 alloys.On thermal simulation press machine,selected different temperature and different deformation speed,did high temperature deformation experiments to TAZ521-xMn(x=0?0.2?0.5and0.8)alloys after heat treatment.Analyzed the effect caused by different temperature and different deformation speed of the rheological performance.We also formed a stress-strain relational model of TAZ521 alloy.And at the same time,analyzed the effect caused by Mn addition on high temperature deformation behavior and dynamic recrystallization of TAZ521 alloy.The experiment results showed that:TAZ521-xMn(x=0,0.2,0.5and0.8)alloys are mainly composed of ?-Mg,Mg2 Sn and some ?-Mg17Al12 phases.The addition of Mn promoted the precipitation of Mg2 Sn and ?-Mg17Al12 phases at grain boundaries and in dendritic arms,and also made dendritic grains refined.There is a certain amount of Al-Mn phases distributed in the Mn-containing TAZ521 solid solution alloys,mainly in the form of particulate Al8Mn5 phases and some Al11Mn4 phases in elongated rod-like form.Some small Al-Mn phases mainly distributed at original grain boundaries,as the cores of heterogeneous nucleation.The compressive test was also be done at room temperature by using TAZ521 alloys of different Mn addition.While the addition of Mn reached 0.2% or 0.5%,the alloys performed better mechanical properties.However,as the Mn content in 0.8%,second phases of particulate form in the structure increased significantly,and the mechanical properties fell dramatically.With the increase of Mn content,the hardness of TAZ521 alloys is generally improved,but the degree of improvement is not very significant.When the Mn content increased from 0.2% to 0.5%,hardness of TAZ521 alloys slightly increased.While Mn content continue increasing to 0.8%,the effect is not obvious.The addition of Mn significantly reduced rheological stress of TAZ521 alloy in high temperature deformation experiments.And in maintaining high temperature conditions,the lower the deformation rate,the effect of stress reduction from Mn became more remarkable.A small amount of Mn addition can also promote dynamic recrystallization nucleation of TAZ521 alloy during high temperature deformation.With the gradual increase of Mn content,the recrystallization promoting effect is more obvious to TAZ521 magnesium alloys.So Mn plays a role of grain refinement in the process of TAZ521 magnesium alloy high temperature plastic deformation.