Study On Preform Modification Of Large-scale Rare Earth Magnesium Alloy Workpiece By Circulating Upsetting-extrusion

As the core component of large equipment,special working condition of large workpiece,complex loading,strict quality requirements,puts forward higher requirements on mechanical properties,Among various kinds of forming methods,plastic deformation process can effectively improve mechanical properties of workpiece,cyclic upsetting as a large plastic deformation process,with significant improvement in the uniformity of the workpiece and enhance the mechanical properties advantages.For the high performance requirements of large components,the use of circular upsetting method for preforming modification,make it before the final forming to achieve the refinement of grain size and enhance the purpose of mechanical properties.In this paper,In this paper,the deformation of Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy large components as the background,the experimental study on the multi-pass cycle upsetting of the alloy.Focus on the impact of multi-pass circulating upsetting to strain,mechanical properties,uniform and microstructure.Studied the impact of multi-pass circulating upsetting to Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy mechanical properties at room temperature.The results show that,With the increase of cyclic upsetting deformation,the tensile strength and yield strength of the alloy are increasing,elongation of the first rise,after the decline,and then increase the trend of change.The precipitation of the second phase is the main cause of the decrease in elongation.The tensile strength and elongation of the alloy after 4 passes were 364 MPa and10.32% respectively,the yield strength and tensile strength were 1.68 times and 2.06 times of that of as-cast.On the other hand,with the increase of the cyclic upsetting deformation,the hardness value of the alloy increases gradually,During the deformation process of 1-3 passes,the hardness curves of different parts of the alloy show obvious divergent state,and theuneven distribution is significant,after 4 passes,the hardness curve starts to cluster and coincides with the average hardness curve.Mechanical properties uniformity was significant improved.Through studied the microstructure of Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy after cyclic upsetting,found that the cyclic upsetting deformation has a strong ability to refine the alloy,With the increase of deformation pass,the refining efficiency of the alloy is gradually reduced,the average grain size is refined from 50.6 um to 7.5 um.Grain size numerical span from 27-38 um at 1 pass,reduce to 7.2-9.8um at 4 pass,microstructure homogeneity was significantly improved.At the same time,the reduction of the extrusion temperature results in a large amount of precipitation of the second phase,Hindered the dislocation motion.Under the combined action of fine grain strengthening and second phase strengthening,the mechanical properties of the alloy are improved remarkably.The finite element simulation software was used to simulate the multi-pass cycle upsetting,revealed the distribution of different field variables in the deformation process.The results show,the distribution of the equivalent stress field has decreased from the necking region to the top and bottom.At the beginning of the deformation,there is a significant strain gradient from inside to outside,the surface strain is the largest,7.3,the bottom strain is the smallest,1.21,the strain difference value reached 6.09.Uneven distribution of strain.With the increase of deformation pass,Under the effect of cumulative strain,the large strain region of the workpiece and the strain uniformity area are expand.4 passes after the deformation,the different parts of the workpiece equivalent strain range reached 10.5-12.5,the strain nonuniformity parameter C decreases from 2.481 to 0.151,strain uniformity was significantly improved.5-6 pass after deformation,the workpiece strain uniformity did not further improve.Through the research of this paper,mastered the cycle upsetting process deformation regularity,determined the optimal deformation pass of Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy at cycle upsetting,which laid the foundation for the popularization and application of the technology,it provides guidance and reference significance for the theoryand practice of prefabricated large-scale workpiece.