Cold hole-expansion was employed on the work of 7B50-T7451 aluminum alloy plate by using a mandrel. The effects of cold hole-expansion on the fatigue life and microstructures of 7B50-T7451 specimens were analyzed by fatigue tests under cyclic loading,and the results were compared with cold-worked holes of 705O-T7451 thick plate. The fatigue striation spacing was observed and measured by SEM. The magnitude of the residual stresses and dislocations introduced into the specimens by hole-expansion were evaluated by an X-ray diffraction and TEM methods. The results show that the 7B50-T7451 aluminum alloy obtained good fatigue enhancement effect with the shrink range of 4% - 6% and the fatigue lifetime were improved up to 29 times compared to the non-cold-expanded ones. The depth of strengthening layer was about 7.3mm, and the maximum residual compressive stress of 387MPa was observed at a distance of lmm to the border of the hole. The residual compressive stress and dislocation cell structure around the cold-worked holes retard the fatigue crack growth rate in propagation stages, and then the whole fatigue life is increased.%采用挤压棒直接冷挤压的方法对7 B50-T7451铝合金厚板进行了孔挤压强化,对比分析了其孔挤压前后疲劳寿命；并与第三代高纯7050-T7451铝合金厚板孔挤压强化效果进行对比.通过扫描电镜(SEM)、透射电子显微镜(TEM)以及X射线应力(XRD)等方法,研究了两种合金的疲劳断口形貌特征、微观组织变化以及孔表层的残余应力场.结果表明,采用4％～6％的挤压量对7 B50-T7451厚板进行挤压强化可取得较好的疲劳强化效果,试件的疲劳寿命是未挤压强化前的29倍；而7050-T7451铝合金厚板疲劳寿命仅是未挤压强化的5.5倍.孔挤压后,7B50-T7451厚板在强化层产生位错缠结及残余压应力,压应力层深度约为7.3mm,最大残余压应力出现在距孔边约lmm处,应力值为387MPa.强化层内形成的位错胞状结构和残余压应力可有效延缓疲劳裂纹的扩展速率,从而提高试件的疲劳寿命.
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