Study On The Homogenization And Thermal Deformation Of Mg-Zn-Zr-RE(Y+Nd)alloy

The requirements of light weight structures provide opportunity as well higher demand for magnesium alloy. Magnesium alloys with rare earth elements have not only the inherent advantages as magnesium alloys, but also corrosion resistance and heat resistance. Therefore, it has become the research focus in the materials field. The rare earth elements would easily get together in the grain boundary and form the non-equilibrium eutectic which has a negative effect on the following deformation. Homogenization heat treatment can eliminate this segregation phenomenon and make the alloy elements distribution even, what’s more, the workability of the magnesium alloys could be improved. Besides, magnesium alloy possess close-packed hexagonal structure and less slip system, so it is difficult to deform. But the combination properties and microstructure can be improved after deformation. Therefore, it can provide theoretical and technical support for the preparation of high-performance magnesium alloy to explore the homogenization process and hot deformation behavior of rare earth magnesium alloy, meanwhile, as are of great engineering value and academic significance.In this paper, Mg-Zn-Zr-RE(Y+Nd) alloy was chosen to investigate the homogenization process and hot deformation behavior. The microstructures of Mg-Zn-Zr-RE(Y+Nd) homogenized under different conditions were tested with OM, SEM, EDS and DSC. The curves of Vickers hardness with homogenization temperature and time were obtained, and the influence of the parameters of heat treatment on the homogenization result was carefully discussed. Homogeneous level of the alloy had been judged by the variance of Vickers hardness distribution. Final, the optimal homogenization process, 500 ℃ × 16 h, was obtained for Mg-Zn-Zr-RE(Y+Nd) magnesium alloy.Hot compression tests of homogenized Mg-Zn-Zr-RE(Y+Nd) magnesium alloy were performed on Gleeble-1500 at deformation temperature ranged in 523K-723 K and strain rates 0.001s-1-1s-1. The results show that the stress and strain curve of Mg-Zn-Zr-RE(Y+Nd) magnesium alloy has a typical feature of dynamic recrystallization. The flow stress rapidly increased and reached a peak at the initial state of deformation, then gradually decreased and finally reached steady-state when stain is large. The material constants of Mg-Zn-Zr-RE(Y+Nd) magnesium alloy for the hot compressive deformation were calculated, Q=181.9026 k J/mol; A=1.8193×1013s-1; α=0.0143MPa-1; n=4.5322. the flow stress equation was established.Basing on the dynamic material model, the process maps of the alloy was established. Combineing with processing maps with deformation microstructure the optimal hot working parameters of homogenized state Mg-Zn-Zr-RE(Y+Nd) alloy were obtained, temperature 660K-700 K, Strain rate 0.008s-1-0.1s-1. Under such hot compression conditions, power dissipation coefficient reached 60%-70%. The dynamic recrystallization occurred under the deformation condition. The main nucleation mechanisms were the original boundary bulging and second phase particle promotion nucleation.