Effect Of Gd And Mn On Microstructure And Properties Of Mg-Gd-Mn Alloy

In this paper,effects of Gd and Mn content on the microstructure and mechanical properties of Mg-Gd-Mn alloys were studied.The as-cast and as-extruded Mg-xGd（x=1,2,4,6,10）and Mg-x Gd-0.8Mn（x=2,4,6,8）alloys were obtained by melting and extrusion tests.Microstructure of alloys were analyzed by the optical microscopy and scanning electron microscope（SEM）.The ICP,DSC,XRD,microhardness,tensile properties at room temperature,thermal compression,weightlessness and other experimental methods were used,The effect of changes of Gd and Mn contents on the law and mechanism of alloys was studied,achieved the following results:（1）With the increase of Gd content,the second phase of as-cast Mg-x Gd alloys increased,and the second phase of homogenization alloys decreased.As-cast and homogenization Mg-x Gd alloys are poor with tensile strength 60MPa and 65MPa.（2）Homogenization alloys produced a lot of dynamic the recrystallized grain in the thermal compression process.With the increase of Gd content,the dynamic recrystallization is more complete,the greater the proportion of dynamic recrystallization,the peak value of the flow stress raised,The maximum value is74MPa.（3）Grain refinement effect of as-extruded Mg-xGd alloys is significant.With the increase of Gd content,the grain size is the smaller.When the content of Gd is more than 4%,the grain refinement effect is not obvious.The minimum average grain size of alloys is 3.35μm.In addition,the second phase was precipitated when the Mg-x Gd alloys were extruded.The mechanical properties of the extruded alloys have been greatly improved,With the increase of Gd content,the tensile strength of the alloys increases continuously When the Gd content is 4%,the tensile strength is 194MPa and the elongation is 35.6%.When the content of Gd is 10%,the tensile strength of the alloy is 270MPa,but the elongation is 16%,the plasticity is poor.（4）With the increase of Gd content,the conductivity of as-cast,as-homogenized,and as extruded the alloys is lower.The conductivity decreases when the alloys were homogenized.After the extrusion deformation,the conductivity began to increase.（5）Gd is helpful to improve the corrosion resistance of the alloys.The as-extruded alloy has the best corrosion resistance but the corrosion resistance of as-cast alloys is the worst.In the as-cast alloy,Mg-6Gd has the best corrosion resistance,the weight loss rate is 29.48 mg.cm^-2.d^-1.The corrosion resistance of Mg-1Gd alloy is the best in homogenized and extruded state,the weight loss rate is 6.45 mg.cm^-2.d^-1 and 2.44mg.cm^-2.d^-1 respectively.（6）The Mg-x Gd-0.8Mn cast microstructure is large and has a large number of dendrite structures.The second phase mainly includes Mg₅Gd phase.With the addition of Gd and Mn,The microhardness of alloy Mg-8Gd-0.8Mn is the highest,The microhardness of the as-cast alloy is 62.3HV.After Mg-x Gd-0.8Mn was extruded,the grain size is obviously refined,the average grain size of Mg-4Gd-0.8Mn is the smallest,the average grain size is 5.56μm,the second phase is Mg₅Gd and Mn.（7）The tensile strength of the as-extruded Mg-xGd-0.8Mn increases with the increase of Gd content.The Mg-8Gd-0.8Mn alloy has the best tensile strength220.3MPa.When the content of Gd is 6%,the maximum yield strength of the alloy is119.8MPa.the elongation of the alloy is optimal,The elongation of the alloy reached29.7%.The comprehensive mechanical properties of alloy Mg-8Gd-0.8Mn are the best with yield strength 115.3MPa,tensile strength 220.3MPa and elongation 25.7%.（8）The conductivity of as-cast,as-homogenized,and as extruded,aging states the alloys decreases with the addition of Gd and Mn.The conductivity of the as-extruded alloy is the highest,and the conductivity of as-extruded Mg-0.8Mn is 34.8%IACS,as-extruded Mg-8Gd-0.8Mn is 12%IACS.The conductivity of the as-cast is the lowest,The conductivity of as-cast Mg-0.8Mn and as-cast Mg-8Gd-0.8Mn is 20.1%IACS and11.5%IACS.（9）The addition of Gd and Mn greatly improved the corrosion resistance of Mg-x Gd-0.8Mn,and the corrosion resistance of Mg-8Gd-0.8Mn alloy is the best.The weight loss rate of the as extruded pure magnesium is 55.31 mg.cm^-2.d^-1.In as-extruded alloys,the weight loss rate of Mg-8Gd-0.8Mn is the smallest.The weight loss rate is 1.2mg.cm^-2.d^-1,The Mg-4Gd-0.8Mn alloy has the maximum weight loss rate that is 3.02mg.cm^-2.d^-1,The weight loss rate of the Mg-0.8Mn is 1.38 mg.cm^-2.d^-1.So the corrosion resistance of Mg-8Gd-0.8Mn is the best.