7B04铝合金超塑性变形过程中的微观组织演变

Microstructure Evolution of 7B04 Aluminum Alloy during Superplastic Deformation

通过高温拉伸试验研究了7B04铝合金超塑性变形的力学特征,采用OM、SEM、EBSD、TEM、FIB分析研究了超塑性变形的组织演变过程。结果表明,试样的最佳变形条件为515℃、3×10^(-4)s^(-1),此时材料的伸长率达到最大值(850%);在变形初期,空洞在空位迁移和拉应力的共同作用下逐渐形成,部分晶粒沿拉伸方向发生碎裂,造成沿拉伸方向的晶粒尺寸略微下降,晶粒纵横比也随之下降,然后晶粒随应变量的增加逐渐长大。7B04铝合金超塑性变形过程中,试样表面在扩散蠕变和晶界滑移的共同作用下出现条纹带,晶界附近形成无沉淀析出带,不存在晶内位错滑移,其超塑性变形机理为伴随扩散蠕变的晶界滑移机制。

The mechanical characteristics during superplastic deformation of 7 B04 aluminum alloy were investigated by high temperature tensile test,and the microstructure evolution of superplastic deformation was observed by optical microscopy,scanning electron microscopy,electron backs cattered diffraction,transmission electron microscopy and focused ion beams.The results indicate that optimal deformation condition is at 515 ℃ and 3×10^(-4)s^(-1),where the elongation rate reaches the maximum value of 850%.At the initial stage of deformation,voids are gradually generated under the combined action of vacancy migration and tensile stress.Partial grains are fractured along the tensile direction,resulting in a slight decrease in grain size along the tensile direction and a decrease in grain aspect ratio,and the grains grow gradually with the increase of strain subsequently.With the proceeding of deformation,stripe bands appear on the surface due to the joint action of diffusion creep and grain boundary sliding,and precipitate free zones are formed near grain boundaries.The absence of intracrystalline dislocation slip is achieved,and the superplastic deformation mechanism is characterized by grain boundary sliding accompanied with diffusion creep.