Mg-9Al-3Si-0.375Sr-0.78Y合金的热变形行为及本构模型

利用Gleeble-3500热模拟试验机对Mg-9Al-3Si-0.375Sr-0.78Y合金试样进行等温恒应变速率压缩实验,研究其在温度250~400℃、应变速率0.001~10s~(-1)条件下的热变形行为。结果表明:在热变形过程中,峰值应力随着应变速率的降低和温度的升高而减小,且峰值应力对应变速率的敏感性随着变形温度的下降而增强。建立了考虑应变的热变形Arrhenius本构模型,模型精度良好,在300,350℃及0.001~10s~(-1)范围内,模型的平均绝对误差分别为1.57%和1.76%;合金的平均变形激活能为183.58k J/mol,平均应变速率敏感指数为0.1616。热变形过程中,α-Mg相呈现明显的动态再结晶特征,β-Mg₁₇Al₁₂相尺寸减小且分布均匀,初生Mg_2Si相较小。在低温(250~300℃)变形时,动态再结晶仅发生在晶界处。在高温(350~400℃)变形时,初生α-Mg晶粒发生了明显的动态再结晶。随着温度的增加和应变速率的降低,再结晶程度提高,再结晶晶粒逐渐长大。

Hot deformation behavior and constitutive equation of Mg-9Al-3Si-0.375Sr-0.78Y alloy

The Mg-9 Al-3 Si-0.375 Sr-0.78 Y alloy specimens were compressed at constant isothermal strain rate by Gleeble 3500 thermal-simulation machine. The hot deformation behavior in the range of 250-400 ℃ and strain rate 0.001-10 s-1were studied. The results show that the peak stress decreases with the decreasing of strain rate and the increasing of temperature, meanwhile, the sensitivity of peak stress to strain rate increases with the decreasing of deformation temperature. In addition, the Arrhenius constitutive equation of hot deformation considering strain is established. The calculated flow stresses are compared with the experimental results, in the range of 300, 350 ℃ and 0.001-10 s-1, the mean absolute errors of the model are 1.57% and 1.76%, respectively. The average deformation activation energy is about 183.58 kJ/mol, and the average strain rate sensitivity index is 0.1616. The α-Mg phases exhibit dynamic recrystallization characteristics obviously. The size of β-Mg17Al12 phases decreases and its distribution becomes uniform, and the morphology of primary Mg2Si phase changes little. At low temperature(250-300 ℃), dynamic recrystallization occurs only at the grain boundary. Under high temperature(350-400 ℃) deformation, the primary α-Mg grains show significant dynamic recrystallization. With the increasing temperature and decreasing strain rate, recrystallization degree increases and recrystallization grain grows gradually.