Effect Of Alloying Element Ag And Impurity Element Fe On Microstructure And Mechanical Properties Of Mg-Gd-Zn-Zr-Ag Alloys

Due to its low density,high specific strength and specific stiffness,Mg alloys have attracted a lot of attention in the fields of automobiles,aviation,etc.However,the inherent shortcomings of Mg alloys,such as poor plasticity,low strength,difficult deformation and easy corrosion,limit its further application.In order to overcome its shortcomings,researchers have adopted processes such as alloying,heat treatment,and deformation to improve properties.In addition,reducing the impurity content in the Mg alloys can also improve the performance of the Mg alloys.Mg alloys containing rare earth(RE)have broad development prospects due to their excellent mechanical properties at room temperature and high temperature.The Mg-Gd-Zn series alloy shows excellent mechanical properties due to the composite strengthening of the LPSO phase and the aging precipitation second phase,but the research on the Mg-Gd-Zn series alloy mainly focuses on the LPSO phase and the aging precipitated?'phase,there are few studies on the?'phase precipitated on the basal of?-Mg.The influence of impurity content on the structure and mechanical properties of the Mg-Gd-Zn alloy is even more lacking.Therefore,in this paper,the influence of Ag content on Mg-Gd-Zn alloys and the reduction of Fe content through the smelting process were investigated.In this paper,Mg-12Gd-1.0Zn-0.5Zr-x Ag(x=0,0.5,1.0,1.5wt.%)alloys with different Ag content were firstly prepared.After the optimal composition ratio of the alloy was studied,the impurity element Fe content of the alloy was reduced by smelting process,and the influence of Fe content on the properties of the alloy was studied.In this paper,by means of metallographic microscope(OM),X-ray diffraction analysis(XRD),scanning electron microscope(SEM),energy spectrum analysis(EDS),transmission electron microscopy(TEM),microhardness test,mechanical property test methods to study the Ag content and the content of Fe on microstructure under different condition,the influence of the performance,based on toughening mechanism of alloy microstructure analysis.The results are as follows:With the addition of Ag,the second phase of Mg-12Gd-1.0Zn-0.5Zr alloy is not affected much,and the main phase of the alloy is the?-Mg,(Mg,Zn)₃Gd phase.When the Ag content is low,the grain refinement of the cast alloy is not obvious,but when the Ag content increases to 1wt.%,the grain refinement of the cast alloy can be significant.After the solid solution treatment,with the addition of Ag,the LPSO phase in the alloy changed from block to lamellar LPSO phase.After extrusion at 400^oC,all the four alloys experienced dynamic recrystallization,but the number of unrecrystallized grains increased with the addition of Ag,mainly because the addition of Ag could promote the formation of lamellar LPSO phase,while lamellar LPSO phase could inhibit the occurrence of dynamic recrystallization during extrusion due to the difficulty of deformation.With the addition of Ag,the fine second phases dynamically precipitated in the alloy after extrusion increase.These grains and the precipitated second phases further increase the strength of the alloy.The tensile strength of the extruded Mg-12Gd-1Zn-0.5Zr-1.5Ag alloy reaches 411 MPa and the yield strength reaches 337MPa,which is 68 MPa and 66 MPa higher than the original alloy,respectively.The addition of Ag can significantly improve the age hardening effect of Mg-12Gd-1Zn-0.5Zr alloy.The tensile strength of the alloy during peak aging is 441MPa,and the elongation is 5.3%,which is an increase of 27 MPa compared to the alloy without Ag addition.The effect of different impurity element Fe content on the structure and mechanical properties of Mg-12Gd-1Zn-0.5Zr-1.0Ag alloy shows that with the decrease of the impurity element Fe content,the alloy grains are significantly refined.And after high temperature solution treatment,the content of the second phase decreases with the decrease of Fe content.After extrusion deformation,the grain size of dynamically recrystallized alloys with low Fe content is significantly smaller than that with high Fe content,and the structure is more uniform.The results of the mechanical properties of the alloy with Fe content of different impurity elements in the extruded state show that Fe content has a significant effect on the mechanical properties of the alloy.With the decrease of Fe content,the tensile strength increases from 371MPa to 384MPa,the yield strength from 254MPa to 261MPa,and the elongation increases from 10.2%to 18.3%.After 32h aging treatment,the Fe content has no significant effect on the Mg-12Gd-1Zn-0.5Zr-1.0Ag alloy,the tensile strength is only increased from 443 to453MPa,the yield strength is increased from 328 to 334MPa,and the elongation is from14.3%increased to 16.7%.