| With the development of high-tech fields such as aerospace and military industry in China,the requirements for high-strength,lightweight and large-scale integrated structures of equipment are put forward.Accordingly,severe plastic def’ormation of ingots is needed to meet the special requirements of such components.In recent years,Mg-RE-Zn alloys containing special long-period ordered structure(LPSO)have become a hotspot of research and development,which have excellent comprehensive properties.But up to now,there are few reports about plastic deformation behavior of Mg-Gd-Y-Zn-Zr alloys with high rare earth content.Therefore,the deformation mechanism and evolution of recrystallization microstructure for the new Mg-11.0Gd-4.0Y-2.0Zn-0.4Zr(GWZK114)alloy during hot compression were systematically investigated in this paper.And the phenomenological dynamic recrystallization model of the alloy was proposed and established.This model was applied to the finite element simulation of the hot deformation process of large-size GWZK114 alloy.Firstly the microstructures of as-cast and homogenized alloy were characterized using advanced test analysis techniques such as SEM and TEM.The results show that the as-cast microstructure consists mainly of a-Mg matrix,18R-LPSO phase,14H-LPSO phase,bulk eutectic phase and rare earth-rich block phase.After homogenization treatment at 500 °C for 16 h,the bulk eutectic phase and the rare earth-rich block phase with highest hardness are basically dissolved,and the tensile properties of the homogenized alloy are obviously improved at room temperature.The tensile strength is 208 MPa and the yield strength is 172 MPa.The deformation mechanism and microstructure evolution of the homogenized GWZK114 alloy were systematically studied by a constant strain rate and isothermal compression test at 300 ℃～500 ℃ and strain rate of 0.01 s-1～10 S-1 The results show that the plastic def-ormation is mainly coordinated by the lamellar 14H-LPSO phase kink and dynamic recrystallization(DRX)behavior at temperatures between 350 ℃ and 450 ℃.At 500 ℃.the deformation is coordinated by dynamic recrystallization.It is found that the kinking behavior of 14H-LPSO phase can icinhibit the occurence of DRX at 350℃～450℃.The dynamic recrystaluzation mechanism is mainly composed of continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX).A phenomenological dynamic recrystallization kinetics model is proposed and established based on the deformation mechanism and the evolution of microstructure.Firstly,considering the non-uniformity of compression deformation,the finite element simulation of the isothermal compression process of the homogenized GWZK114 alloy is carried out to determine the strains of the locations for microstructure observation,and the fraction of dynamic recrystallization and the grain size of recrystallized grains were quantitatively counted.A model of dynamic recrystallization fraction in accordance with Avrami equation was established.At the same time,considering the restraining effect of 14H-LPSO phase kinking on DRX at 350 ℃～450℃,a power law function is added to the original model to describe the gradient structure successfully.Compared with the experimental results of uniaxial compression and repetitive upsetting extrusion(RUE),this model can accurately predict the dynamic recrystallization fraction and dynamic recrystallized grain size at large strain deformation.Numerical simulation of thermal deformation of GWZK114 alloy with large size was carried out.Microstructure evolution model was compiled by Fortran language.Based on the subroutine of DEFORM-3D software,the coupled simulation of physical and microstructural fields of GWZK114 alloy during hot compression was carried out.The results show that the predictions of dynamic recrystallization fraction and grain size are in good agreement with the experimental results,verifying the accuracy of the phenomenological dynamic recrystallization kinetics model. |
PDF Full Text Request