Effect Of Rare Earth Elements(Ce,Y,Gd)on The Microstructure And Evolution Of ZK Magnesium Alloy

As an important deformed magnesium alloy,ZK magnesium alloy has been practically applied in many fields.The role of rare earth elements in improving its mechanical properties and deformation processing properties has also been agreed by many researchers.However,it is found from the current research that the study on the existence of different rare earth elements in ZK magnesium alloy is obviously insufficient,and the comparative study on the influence of rare earth elements on the microstructure characteristics of ZK magnesium alloy is rarely involved.Although a large number of literatures have reported the effects of rare earth elements on the deformation properties and microstructure of alloys,there is a lack of systematic research on the effects of rare earth elements on the whole processing process of alloys.Therefore,the representative rare earth elements Ce,Y,Gd are selected to be added into ZK31 and ZK61 respectively.The ingot is made by semi continuous casting method.In order to study the influence of different rare earth elements on the microstructure and evolution of the alloy,homogenization annealing and hot compression deformation are carried out according to the usual deformation process.In addition,the change of the content of solid solution,the size of grain and the structure of compound in as cast,homogeneous and variable forms was analyzed.In this paper,the solid solution of the elements in the as-cast and homogeneous alloys was determined by the method of chemical phase separation and ICP measurement.The solid solution ability of different rare earth elements in ZK magnesium alloy and the effect of different homogenization process on the solid solution of alloy elements were analyzed.The results showed that Ce had the lowest solid solution,Y and Gd had almost the same solution.The solution of rare earth elements decreased with the increase of Zn content.After the homogenization treatment,the solid solution amount of rare earth element Ce increased with the extension of the homogenization time,while the solid solution amount of Y and Gd decreased with the extension of the homogenization time.The solid solution quantity of Zn increased with the time of homogenization increase in ZK31-RE,and decreased in ZK61-RE.The as cast and homogeneous microstructure of alloy were observed and studied,the effects of different rare earth elements on the grain size and compound phase of alloy were analyzed by the OM,SEM and XRD.The results show that the addition of rare earth elements has the effect of refining grains of as-cast alloy,and Ce has a relatively strong refining ability.After homogenization,the grain size of alloy grows obviously.but rare earth elements can inhibit the grain growth.Ce is added to the ZK magnesium alloy to form?Mg Zn?₁₂Ce intermetallic compound?T phase?and the compound phase does not change after homogenization.Y and Gd are added to ZK31 magnesium alloy to form Mg₃Y₂Zn₃?W phase?and Mg-Y-Zn phase,Mg₃Gd₂Zn₃?W phase?and Mg-Gd-Zn phase.Y and Gd are added to ZK61 magnesium alloy to form Mg₃Y₂Zn₃?W phase?,Mg₃YZn₆?I phase?and Mg₃Gd₂Zn₃?W phase?,Mg₃Gd Zn₆?I phase?.After homogenization,only Mg₃Y₂Zn₃ and Mg₃Gd₂Zn₃?W phase?in the ZK-Y and ZK-Gd magnesium alloys.The hot compression deformation of ZK-RE magnesium alloy after homogenization treatment at 400?for 12 hours was carried out by Gleeble 3500.The microstructure under different deformation were observed.The influence of rare earth elements on deformation properties and deformation microstructure of alloy was discussed.The results show that with the addition of rare earth elements,the overall flow stress level of alloy increases,and the sequence is Ce>Y>Gd.The whole deformation of alloy shows a softening dominated by dynamic recrystallization.Both the increase of deformation and the addition of rare earth elements increase the dynamic recrystallization of alloy.