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利用Gleeble-3500试验机,在300~450℃和0.1~10 s~(-1)的变形条件下,研究了大规格铸锭晶粒尺寸的不均匀性对新型高强Al-7.68Zn-2.12Mg-1.98Cu-0.12Zr合金热变形行为的影响。SEM观察表明,大铸锭表层的晶粒尺寸比心层细小。热变形过程中,细晶组织(铸锭表层)的流变应力在高温和低应变速率条件下低于粗晶组织(铸锭心层)。计算得到表层和心层组织的热变形激活能分别为140和125.4 kJ/mol。基于位错密度理论,利用一种两阶段型本构方程分别预测了粗晶和细晶组织的流变应力,并建立了不同晶粒度组织的动态再结晶软化方程。电子背散射衍射(EBSD)观察表明,合金在300~400℃条件下发生动态回复,在450℃和低应变速率速(0.1 s~(-1))条件下出现动态再结晶(DRX)现象,动态再结晶晶粒在原始大角度晶界上形核。由于表层(细晶)组织的晶界密度高,因此其动态再结晶程度高于心层(粗晶)组织。
Using the Gleeble-3500 testing machine, the inhomogeneity of the grain size of the large size ingot was studied under the deformation conditions of 300 ~ 450 ℃ and 0.1 ~ 10 s ~ (-1). The effects of the new high strength Al-7.68Zn-2.12Mg Effect of Hot Deformation Behavior of -1.98Cu-0.12Zr Alloy. SEM observation shows that the grain size of the ingot surface is smaller than that of the heart layer. During thermal deformation, the flow stress of fine grain structure (ingot surface layer) is lower than that of coarse grain structure (ingot core layer) at high temperature and low strain rate. The calculated thermal activation energy of the surface layer and the core layer were 140 and 125.4 kJ / mol, respectively. Based on the dislocation density theory, a two-stage constitutive equation was used to predict the flow stress of coarse and fine grains respectively and the dynamic recrystallization softening equation of different grain size was established. The electron backscatter diffraction (EBSD) observation shows that the alloy dynamically reacts at 300-400 ℃ and the dynamic recrystallization (DRX) occurs at 450 ℃ and 0.1 s -1 (-1) Dynamic recrystallization grains nucleate at the original large-angle grain boundaries. Due to the high grain boundary density of the surface (fine grain) structure, its dynamic recrystallization is higher than that of the heart layer (coarse grain).