The Thermal Deformation Behavior And Evolution Of Hot Spinning Microstructure And Property Of Mg-7Gd-5Y-0.6Zn-0.9Zr Magnesium Alloy

With increasing requirements of environment protecting and energy saving, the application of magnesium and its alloy gained more and more attention. So far, whether the automotive industry or the aerospace industry are actively trying to apply magnesium alloy, and constantly tapping the potential of its application. However, because of the poor heat resistance and creep resistance, low strength and poor formability, the application of traditional magnesium alloy is limited. The addition of RE elements can not only improve the strength of magnesium at the ambient and high temperature, but also improve the heat resistance, creep r esistance and the strength of heat treatment.In the present study, the microstructure evolution and the strengthening mechanism of Mg-7Gd-5Y-0.6Zn-0.9Zr magnesium alloy was investigated. Besides, in order to research the possibility to form the lightweight rotational co mponents with thin wall by spinning to meet the needs of aerospace industry, we firstly studied the hot deformation behavior, calculated the activation energy and constructed the hot processing maps of the alloys, based on which, the spinning experiments were carried and the microstructure evolu tion during spinning were analyzed.The results are as follows: Mg-7Gd-5Y-0.6Zn-0.9Zr magnesium alloys mainly consisted of α-Mg, Mg3(Gd,Y,Zn) phases, 14H-LPSO phases, the cubic phases rich in RE and Zr. After solution for 10 h at 500 ℃, the strength reached the peak. Because of the decomposition of Mg3(Gd,Y,Zn) phases and the RE elements diffuse to grains. The aging strength peak was reached at 210 ℃ and 120 h, but the elongation reduced obviously, which was caused by the precipitation of secondary phases particles at grain boundaries.With the increase of temperature and decrease of strain rate, the flow stress of Mg-7Gd-5Y-0.6Zn-0.9Zr magnesium alloy decreased during thermal compression, but the volume fraction of dynamic recrystallization increased. The defor mation activation energy was 260.85KJ/mol. The hot processing map shows that the re asonable deformation parameters of this alloy consisted of three main regions: the low temperature and low strain rate region with temperature from 375 ℃ to 440℃ and strain rate from 0.001s-1 to 0.006s-1, the middle temperature and middle strain rate region with temperature from 440℃ to 460℃ and strain rate from 0.006s-1 to 0.2s-1, the high temperature and high strain rate region with temperature from 460℃ to 475℃ and strain rate from 0.2s-1 to 1s-1. The instability occurred deforming at low temperature and high strain rate and the grain grew deform ing at high temperature and low strain rate.The reasonable temperature for spinning of Mg-7Gd-5Y-0.6Zn-0.9Zr magnesium alloy is from 440℃ to 460℃. The deformation was not uniform along the thickness direction, when the reduction ratio was small, and the deformation of outer surface was larger than inner surface. With the increase of reduction ratio, the materials’ strength increased firstly, and then decreased because of the occurrence of micro crack.