Study On Non-equilibrium Structure And Properties Of Mg-Zn(Sn) And Mg-Zn-Sn Magnesium Alloys

In recent years,Mg-Zn-Sn alloys have received extensive attention in the world because of their better aging strengthening and high-temperature resistance.Under the condition of metal-mold casting,Mg-Zn-Sn alloys are easy to form a non-equilibrium eutectic structure,which is the alloy of non-eutectic composition on the phase diagram of the eutectic structure due to the fast cooling rate.The non-equilibrium structure has an important influence on the properties of magnesium alloys,but there are few studies on the non-equilibrium structure of Mg-Zn-Sn alloys.In this paper,Mg-Zn,Mg-Sn and Mg-Zn-Sn alloys with different composition were prepared by metal mold casting.The influence of Zn and Sn content on the as-cast structure of the alloys was studied,the Schiel equation was used to calculate the number of non-equilibrium eutectics;The mechanical properties of the alloys at room temperature and high temperature was studied by compression tests,the work hardening rate-stress curve was drawn,the solid solution content of Zn and Sn in the alloys were measured by EDS,and the influence of the as-cast structure was analyzed on the mechanical properties;The Mg-Zn-Sn alloys with good plasticity were subjected to compression deformation at different temperatures and strain rates,the thermal deformation constitutive equation was constructed,the activation energy and activation volume were calculated.Thereby,the plastic deformation mechanism of the alloys was analyzed.The results of the non-equilibrium structure study show that Mg-Zn and Mg-Sn alloys produced eutectic structures when Zn?4wt.%and Sn?3wt.%,respectively,and divorced eutectics appear in Mg-5Zn-5Sn alloys.With the increase of Zn and Sn content,the eutectic integral increased,and the non-equilibrium eutectic integral of Mg-10Zn alloys reached 15.6%.The research results of mechanical properties reveal that the compressive strength and compressibility(ie plasticity)of the alloys have an increased trend first and then decreased with the increase of Zn and Sn content at the room temperature,because on the one hand,the solid solution content of Zn and Sn increases with the increase in content,the alloys produced a solid solution strengthening effect.However,on the other hand,if the content of Zn and Sn exceeds a certain value,non-equilibrium lamellar eutectic structures were produced.Cracks are easy to initiate at the eutectic structure during compression,which reduces strength and toughness.When compressed at 250°C,the strength of Mg-Zn alloys increased first and then decreased with the increasing of Zn content,while the strength of Mg-Sn and Mg-Zn-Sn alloys increased with the increasing of Sn content because of the Mg₂Sn is a high-temperature resistant phase and the Mg Zn phase is not resistant to high temperatures.By constructing the thermal deformation constitutive equation of Mg-2Zn-2Sn alloys,the deformation activation energy Q=175.865k J/mol;the strain rate sensitivity index m=0.164;the activation volume V=12?106b³ were calculated,it shows that the alloys had non-basal surface slip occurs in the range of 200?350?.