超轻细晶Mg-8.4Li合金的低温超塑性

Mg-8.4Li合金铸锭经573 K×24 h均匀化处理和473 K温轧得到1.5 mm厚板材,总加工率为92.5%.该板材经盐浴再结晶退火后在473 K,应变速率1.67×10-3s-1条件下获得500%的超塑延伸率.唯象学计算的应变速率敏感性指数为0.47,反映晶界滑移是其主要变形机理.利用透射电子显微镜和光学显微镜研究了板材573 K×1 h盐浴退火和超塑性变形后的组织,发现盐浴退火后的晶粒尺寸为2.4μm,超塑变形后标距内晶粒尺寸为5.8μm,发生了一定程度的晶粒长大,这与原子扩散机理有关.利用扫描电镜观察了超塑变形后试样的断口形貌,发现断口中韧窝细小而深,呈圆形分布,保持了晶粒等轴化...

Low-Temperature Superplasticity of a Ultralight Fine-Grained Mg-8.4wt%Li Alloy

A 1.5 mm-thick Mg-8.4wt%Li alloy sheet was obtained through warm-rolling at 473 K with a total reduction of 92.5% after melting, casting, ingot homogenization annealing at 573 K for 24 h. A percentage elongation up to 500% was demonstrated for such sheet at 473 K and initial strain rate of 1.67 × 10^-3/sec after said 1.5 mm sheet passed the recrystallized salt bath annealing. The strain rate sensitivity index was 0.47 through phenomenological calculation, indicating that grain boundary sliding is the dominant deformation mechanism. The microstructure of such sheet after 573 K × 1 h salt bath annealing and superplastic deformation was studied by TEM and optical microscope. It was found that the grain size after salt bath annealing was 2.4 μm and that within the gauge length of specimen after superplastic deformation was 5.8 μm, indicating the occurrence of certain grain growth which is relevant to the atomic diffusion mechanism. SEM was used to examine the fractograph of specimen after superplastic deformation. It was found that the dimples are fine, deep and roundly distributed, thus retaining the original feature of equiaxial grains.