Microstructure,Texture And Mechanical Properties Of Equal Channel Angular Pressed (ECAPed) Mg-Sn Based Alloys Containing Icosahedral Phase

Magnesium alloys has a serious of advantages,such as low density,easy to recycle,high specific strength and specific stiffness and so on,so Mg alloys have been used in automobile,aviation,electronics,military and other industrial fields.However,the relatively low strength and poor high temperature stability still limit the Mg alloys' widely using.Mg-Sn alloys has a better overall performance and high temperature stability than the traditional Mg-Al-Zn and Mg-Zn-Zr alloys due to their good deformability and containing high melting point Mg2 Sn phase(770 ?).Furthermore,previous studies have shown that the extra addition of Zn and/or Al in Mg-Sn alloys could enhance the age hardening response effectively.In addition,previous reports indicated that I-phase could be obtained in Mg-Sn alloys by selecting a suitable Zn/Al mass ratio using the normal casting method.And as a strengthening phase,the I-phase has a positive effect on improving the performance of the alloys.So the overall performance of Mg-Sn alloy is expected to get an obvious improvement by only add the cheap Zn and Al,which will be helpful for the further development of the non-RE heat-resistant Mg alloys.So this paper combined add Zn and Al into Mg-Sn alloy and proceed the Equal channel angular pressing(ECAP)to find the optimum alloycomposition.Then,conducted the aging treatment on this alloy to explore the effect of aging prior to ECAP on the alloy's tensile properties.Finally,In order to maximize the strengthening effect,this paper studied the influence of the number of ECAP passes on the alloys' mechanical properties.Using the optical microscope(OM),X-ray diffractometer(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)to analyze the microstructure and phase composition of the alloys,and characterize the mechanical properties of the alloy by measuring micro vickers hardness and room temperature tensile properties.The results showed that:(1)After adding 5%,6% and 7%(wt.%)of Zn in Mg-8Sn-2Al alloy and 2 passes of ECAP,Mg-8Sn-6Zn-2Al(TZA862)alloy showed the best strength and elongation due to relatively strong fine-grain strengthening and precipitation strengthening effect.Note that,the I-phase could be found in TZA862 and TZA872 alloy.(2)Mg-Sn alloys has relatively good timeliness,so conducted the aging prior to ECAP on TZA862 alloy,and results showed that APE treatment can not only improve TZA862 alloy's strength through decreasing the grain size,increasing the fraction of fine particles and texture intensity,but also can enhanced the ductility by reducing the amount of large non-deformed particles.(3)Through conducted different passes of ECAP on TZA862 alloy,it can be found that the 6p sample showed the best overall performance.Due to its relatively small average grain size,relatively strong precipitation strength and relatively high texture intensity,6p sample shows the relatively high strength.And relatively small amount of coarse particles and relatively high Hc make it has a better elongation.Although8 p sample has the strongest yield strength(YS),both the relatively lowworking hardening capacity and a amount of coarse secondary phase have a negative effect on the plasticity.