【摘要】 采用多向锻造与轧制（MDFR）制备了Mg-4.4Li-2.5Zn-0.46Al-0.74Y合金,利用拉伸机、OM和XRD等研究了热拉伸流动应力、组织演变、本构模型与变形机理。结果表明,合金多向锻造晶粒细化机理为机械式剪切破碎与动态再结晶细化。合金在523～573 K时,热变形组织主要发生动态回复与动态再结晶;≥573 K时,热变形组织主要发生晶粒长大;在623 K发生由晶粒长大引起的应变硬化。合金退火组织由α（Mg）、β（Li）、Al₂Y、Al₁₂Mg₁₇、LiAl和Mg₂Y相组成。本构分析表明,合金应力指数为4.4,变形激活能为120.40 kJ/mol;623 K、1.67×10^-4s^-1条件下,对应240%延伸率的位错密度和数量与原子扩散计算表明,合金在该条件下的变形机理为晶格扩散控制的位错蠕变。晶粒长大模型确定该条件下的晶粒长大指数q=2,比例因子α’=0.2。更多还原

【Abstract】 Mg-Li alloys have potential applications in the aerospace, military, electronics, and automobile fields due to their superlight density, extremely high specific stiffness, high specific strength, damping, and electromagnetic shielding properties. Due to the limited slip systems of Mg and hcp-structuredα（Mg） at room temperature, magnesium and α（Mg）-based alloys are difficult to deform; thus, it is significant to investigate the high-temperature deformation behavior to address this issue. Thus, in this study,an ultralight α（Mg）-based Mg-4.4 Li-2.5 Zn-0.46 Al-0.74 Y alloy was fabricated via multi-directional forging and rolling, and its flow stress, microstructural evolution, constitutive modeling, and deformation mechanism at elevated temperatures were investigated by tensile tests, OM, and XRD. The results indicate that the grain refinement mechanism of this alloy processed by multi-directional forging（MDF） exhibits mechanical shearing fragmentation and dynamic recrystallization（DRX）. Additionally, the flow stress results demonstrate that strain-hardening occurred at 623 K due to grain coarsening, and microstructural evolution reveals that dynamic recovery and DRX occurred at tensile temperatures of 523-573 K; however,grain coarsening primarily appeared at 573 K（or more）. XRD analysis demonstrates that this alloy comprised α（Mg）, β（Li）, Al₂ Y, Al₁₂Mg₁₇, LiAl, and Mg₂ Y phases, and hyperbolic sine constitutive analysis reveals that the stress exponent was 4.4 and the activation energy for deformation was 120.40 k J/mol. The calculated results for dislocation density, number of dislocations in a grain, and atomic diffusion at 623 K and 1.67 × 10-4 s-1 corresponding to elongation-to-failure of 240% indicate that dislocation creep controlled by lattice diffusion governed the deformation mechanism under this condition. Predictions by grain growth models indicate that the calculated grain sizes were in good agreement with the practical grain sizes at 623 K and 1.67 × 10^-4 s^-1 when the grain growth factor was equal to 2 and proportional factor was 0.2.更多还原