预拉伸对7050铝合金断裂韧性的影响

Effect of prestretching on fracture toughness of 7050 aluminum alloy

采用光学显微镜、扫描电镜、透射电镜、常温拉伸及断裂韧性实验,研究预拉伸对7050铝合金板材力学性能和断裂韧性的影响。结果表明:预拉伸引入大量位错,时效过程中可以成为粗大平衡相η相的有利形核点;随着预拉伸变形量的增大,η相的尺寸增加,板材的强度降低;晶界析出相间距增大,呈不连续分布,晶内晶界之间的强度差减小,板材具有更高的变形抗力,断裂韧性提高;预拉伸变形量增大导致晶界沉淀相粗化,无沉淀析出带变宽,变形过程中容易产生应力集中,对韧性不利;综合组织结构的正负面影响,随着预拉伸变形量的增大,板材的断裂韧性逐渐增大。

The effects of prestretching on the tensile property and fracture toughness of 7050 aluminum alloy plate were investigated by optical microscopy,scanning electron microscopy,transmission electron microscopy,tensile and toughness tests.The results show that many dislocations are generated in the prestretch process,and the dislocations can provide efficient nucleation sites for larger equilibrium phase η in the ageing.With increasing the prestretching,the size of the η phase increases,which results in the reduction in the strength.Furthermore,the distance between precipitates in the grain boundaries becomes larger.The precipitates discontinuously distribute in the grain boundaries.The strength-differential between the matrix and the boundary is reduced,which promotes more homogeneous deformation,and is beneficial to the fracture toughness.With increasing the prestretching,the precipitates in the grain boundary become coarser,and the precipitate free zones become wider,which assists the strain concentration in the deformation process and results in continuous decrease in the resistance to fracture.In a word,with increasing the prestretching,the fracture toughness increases.