The Microstructure Analysis And LPSO Phase Evolution Of Mg-13Gd-4Y-2Zn-0.5Zr Alloy After Hot Compression Processing

Rare earth magnesium alloy has the advantages of both traditional magnesium alloy and the characteristics of high strength and heat resistance, and has been widely used in the automotive, electronic 3C and aerospace and other fields. The special LPSO phase in the Mg-RE-X alloy system can significantly improve the strength and the plasticity of the alloy,and improve the comprehensive mechanical properties. it can be for plastic deformation of the alloy forming process provide an important theoretical basis to study the microstructure and changes of LPSO phase in distribution,morphology and evolution laws of strain mode in plastic deformation process under different deformation conditions. In this paper, with the Gleeeble 3500 thermal simulation machine, Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy has been deformed of hot compression experiment in different deformation rates and deformation temperature. By the means of optical microscopy(OM), scanning electron microscopy(SEM) with spectroscopy(EDS) and XRD,the phase and chemical composition analysis of alloys were studied. Then discuss and summary the evolution of LPSO phases in the microstructure.In the microstructure of the samples after homogenization and thermal compression,α-Mg matrix grain, eutectic phase α-Mg / β(Mg24 Y5) distributed in the grain boundaries, the second phase LPSO-Mg12 ZnY distributed in grains and ternary phases W and I were observed.There were also some second phases(LPSO-Mg12ZnY) with less quantity and having not yet fully grown in the microstructure of casted samples. In addition, the grain size after thermal compression increases with the deformation temperature and strain rate increasing.Under different experimental conditions the LPSO phase in alloy substantially presented in three forms, namely the fine lamellar within the grains, the stick-like shape distributed in the grain boundaries, and the short rod or small block shape within the grain. It is noteworthythat the fine lamellar LPSO phase can be observed in all the alloy, but at a strain rate of0.01s-1 with the deformation temperature of 450 ℃ and 500 ℃, in addition to this fine lamellar form, the fine lamellar LPSO phase in the grain portion disconnected from each other, breaking down into short rod or small block forms, LPSO phase in this form can make a dispersion strengthening effect on the matrix phase; meanwhile, a new form of LPSO structure appears in the samples under these two states——rod-like LPSO along the grain boundary, this form LPSO phase can also play a strengthen role by the mechanism of "short fiber reinforced".Alloys at 300℃ of hot compression temperature, all the samples have cracked, so the alloy deformation temperature should be selected higher than 300℃. When the strain rate is at 0.01s-1 and the deformation temperature is among 450-500 C, the alloy has a greater microstructure, and this is the best condition state for the alloy to carry on plastic deformations.