AZ31镁合金超塑性及其变形机制图

Superplasticity and Deformation Mechanism Map of AZ31 Magnesium Alloy

在温度为400～440℃、应变速率为10-2～10-4s-1范围内,研究挤压态AZ31镁合金的超塑性。结果表明,当应变速率较高时,颈缩是超塑性断裂的主要原因。温度越高,应变速率敏感指数m值越大,AZ31镁合金的超塑性伸长率越高。当应变速率较低时,空洞扩张是影响超塑性断裂的主要原因,温度越高,超塑性伸长率越低。研究了超塑性变形机理,建立了超塑性变形机制图,结果表明,温度为400℃或420℃、应变速率较低时,AZ31镁合金的超塑性变形属于溶质拖曳的位错蠕变机制;当应变速率较大时,属于攀移控制的位错蠕变机制。温度为440℃时,AZ31镁合金的变形机制符合晶格扩散控制的位错蠕变。

The superplasticity of as-extruded magnesium alloy was examined with strain rate of 10-2~10-4s-1 at 400~440℃. The results reveal that necking contract is dominant in tensile fracture of the specimens with a higher strain rate. With increasing in temperature,m value (strain rate sensitivity index) and elongation of the alloy are increased. With a lower strain rate,tensile fracture mechanism is controlled by cavity expansion,resulting in the decrease of elongation with increasing in temperature. Superplasticity deformation mechanism map was drawn by analyzing deforming mechanism. The results indicate that,with a low strain rate,at 400℃ or 420℃,deformation mechanism is characterized by dislocation creep controlled by the solute drag,while with a higher strain rate,it is characterized by the dislocation creep controlled by climb. At 440℃,deformation mechanism of the as-extruded alloy is accordant with the dislocation creep controlled by lattice diffusion.