Microstructure,properties And Hot Compression Behavior Of Mg-11Gd-3Y-xZn-0.5Zr Alloys

As a new type of lightweight alloy,magnesium alloy has become a research focus because of its small density,high specific strength,and high specific stiffness.It has been widely used in automotive,aerospace,electronic products,and medical fields,but its high temperature performance is poor.Limiting the application of magnesium alloys in some aspects.After adding rare earth elements,the high temperature strength of magnesium alloys can be improved,but the high rare earth content will reduce the plasticity of magnesium alloys.Therefore,how to make magnesium alloy with high rare earth content have sufficient plastic deformation properties at the same time as high strength is necessary.In this paper,a Mg-11Gd-3Y-0.5Zr alloy with high rare earth content was used,and by adding different amounts of Zn(addition amounts are 0,0.3,0.7,1.1,1.5,wt.%,the same below)to study the effect of different Zn content on structure and property,the hot compression deformation behavior of those alloys was studied through hot compression simulation experiment.The results of the study are as follows:The as-cast Mg-11Gd-3Y-0.5Zr alloy is composed of?-Mg,Mg₅Gd and Mg₂₄Y₅phases.After Zn was added,those alloys were composed of?-Mg,Mg₅Gd and new lamellar Mg₁₂Zn Y phase.The Mg₂₄Y₅phase disappeared.With the increase of Zn content,Mg₁₂Zn Y phase increases,and the precipitation of the Mg₅Gd phase is promoted,and second phase is gradually distributed in intermittent network.The addition of an appropriate amount of Zn can significantly refine the grain size of the alloy,and the grain size is smallest when the Zn content is 1.1%.Within the scope of this study,with the increase of Zn content,room temperature tensile strength and elongation of as-cast alloys decreased first,then increased and then decreased.Both the tensile strength and elongation reached the maximum when the Zn content is 1.1%.After solution-treated of as-cast alloys at 525?for 10 h,alloy structure is more uniform.In the matrix alloy without Zn,all Mg₂₄Y₅phase was dissolved in the matrix,and only a small amount of Mg₅Gd phase remains was undissolved.The lamellar Mg₁₂Zn Y phase in alloys containing Zn did not significantly dissolved,and with the increase of Zn content,Mg₁₂Zn Y content increased.After solution-treated alloys were kept at 225?for 12 h,the alloy without Zn was composed of?-Mg,Mg₅Gd and Mg₂₄Y₅phases.After Zn was added,the grain size was refined,and the diffraction peaks of Mg₂₄Y₅phase disappeared.In addition to the precipitated phase of Mg₂₄Y₅,a new lamellar phase Mg₁₂Zn Y remained,and with the increase of Zn content,Mg₁₂Zn Y and Mg5Gd increased.The tensile test results of aging alloys at room temperature(25?),200?,250?and 300?show that within the scope of this study,at the same temperature,with the increase of Zn content,the tensile strength decreased first,then increased and then decreased,and reached the maximum when Zn content is 1.1%.Except for the alloy with Zn content of 1.5%,with the increase of temperature,the tensile strength increased first and then decreased,and reached the maximum at 200?,showing an abnormal temperature effect of tensile strength.When the Zn content is 1.1%,the alloy not only has high strength,but also has the largest elongation and excellent comprehensive mechanical properties.The solution-treated Mg-11Gd-3Y-x Zn-0.5Zr alloys were subjected to hot compression experiments at temperature of 350??500?and strain rate of 0.002s^-1?1 s^-1.The result show that the true stress-strain curves of the alloys all show obvious dynamic recrystallization characteristics.The peak stress and flow stress of the alloys decreased with increase of temperature or decrease of strain rate.At the same temperature and strain rate,with the increase of Zn content,the peak stress of the alloy increased.The hot compression activation energy of each component alloy were calculated and the constitutive equation were constructed.Within the scope of this study,compared to the alloy without Zn,the activation energy of the alloy increased significantly when 0.3%Zn was added,but when the Zn content was continued to increase(0.7%?1.5%),the activation energy of the alloys didn?t change significantly.Analysis of the alloys after hot compression show that the recrystallization of the alloys was more obvious with the increase of temperature or the decrease of strain rate.At same temperature and strain rate,compared to the alloy without Zn,the structure of alloy with 0.3%Zn was significantly refined after compression,and the recrystallization process was delayed.Continued to add Zn,the grain size continued to decrease,and reached the smallest when the Zn content is 1.1%,and then slightly increased.Based on the dynamic material model,the processing maps of alloys were drawn,and the appropriate technology of alloys were analyzed.The deformation performance of Mg-11Gd-3Y-0.7Zn-0.5Zr alloy is the best at strain of 0.3 within the scope of this study.