LAUSR

Al–Zn–Mg–Sc–Zr alloy samples were annealed to four different states (under-aging, peak-aging, over-aging and double-aging) and then thoroughly investigated by means of electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), tensile and fatigue crack growth rate tests to explore the influence of annealing treatment on microstructure and fatigue crack growth behavior. The results indicate that Al3(Sc,Zr) particles can effectively refine grains and enhance tensile properties and fatigue properties. After annealing treatment, the under-aged sample and double-aged sample obtained average grain sizes of 4.9473 and 4.1257 μm, and the maximum value of yield/tensile strength (561 MPa/581 MPa) was obtained in peak-aged state. In the Paris region, fatigue crack growth rate, crack deflection and bifurcation, crack blunting and inter/trans-granular propagation were discussed based on data fitting and Laird model and Griffith theory. And the results show that the under-aged sample possesses the best resistance to fatigue crack propagation and the most tortuous and bifurcated crack path. For all samples, the fatigue crack growth rate in the rupture region was inversely proportional to yield strength.摘要本文采用电子背散射衍射(EBSD)、透射电子显微分析(TEM)、扫描电子显微分析(SEM)、 室温拉伸性能测试和疲劳裂纹扩展测试的方法研究了4 种时效处理(欠时效、峰时效、过时效和双级 时效)对Al–Zn–Mg-Sc–Zr 合金的显微组织和疲劳裂纹扩展行为的影响。 结果表明:合金中的Al3(Sc,Zr) 粒子能显著地细化合金晶粒、提升拉伸性能和抗疲劳裂纹扩展性能。其中,欠时效样品和双级时效样 品的平均晶粒尺寸分别为4.9473 μm 和4.1257 μm,峰时效处理后样品达到最高的屈服强度和抗拉强 度(561 MPa 和581 MPa)。基于Laird 模型和 Griffith 理论,本文研究了合金在Paris 区域中的裂纹 扩展速率、裂纹曲折与分叉、裂纹钝化与裂纹的沿晶和穿晶扩展行为。结果表明,欠时效样品表现出 最佳的抗疲劳裂纹扩展性能,其裂纹路径最为曲折、裂纹分叉最多。在高速扩展区域中,所有样品的 疲劳裂纹扩展速率均和屈服强度负相关。