超轻细晶Mg-8.4Li合金的低温超塑性

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

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,保持了晶粒等轴化的特点.

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 de...