针对工业化生产的7N01铝合金板材,采用拉伸实验、疲劳实验和微观组织结构表征等手段研究了预拉伸变形对欠时效态7N01铝合金板材疲劳性能和疲劳断裂特征的影响。结果表明,预拉伸变形量增大至20%,欠时效态7N01铝合金板材中合金相粒子的形状、尺寸、数量、分布以及薄带状晶粒的尺寸和形状基本保持不变。然而,板材表现出明显的加工硬化效应,其屈服强度、抗拉强度和显微硬度分别由181 MPa、233 MPa和95 HV增大至254 MPa、271 MPa和117 HV,延伸率从23.2%降低至5.2%。在应力175 MPa、应力比R = 0的疲劳循环加载条件下,随预拉伸变形量的增加,欠时效态7N01铝合金板材的疲劳寿命呈现出先缩短再延长又缩短的趋势。未预拉伸变形试样的疲劳寿命为6.06 × 10⁵ cyc,5%预拉伸变形可将铝板的疲劳寿命延长75%,达到了1.06 × 10⁶ cyc,而3%和20%的预拉伸变形将铝板的疲劳寿命分别缩短至4.21 × 10⁵和2.89 × 10⁵ cyc。5%~16%预拉伸变形使欠时效态7N01铝合金板材基体中形成均匀分布的高密度位错或位错胞的显微组织,可将合金板材的疲劳寿命延长23%以上。

7N01 aluminum alloy is the main load-bearing structure material for bullet train bodies due to its high specific strength, high specific stiffness, good magnetic-shielding ability, strong corrosion resistance, and good formability and weldability. The fatigue performance of materials and components used in bullet trains determines their security. It is unavoidable that there is pre-deformation during the assembly process of aluminum alloy components, which will influence the active service and fatigue performance of the aluminum alloy. It is important not only to clarify the relationship between pre-deformation and fatigue performance but also to reveal the mechanism of pre-deformation on the fatigue fracture of 7N01 aluminum alloy, to ensure the security of the bullet train. In this study, the effect of pre-tensile deformation on the fatigue property, fatigue fracture initiation, and fatigue crack propagation characteristics of a commercial 7N01 aluminum alloy plate at under-aged conditions was studied using tensile and fatigue tests combined with microstructure analysis. As the pre-tensile deformation increased to 20%, the results showed that the shape, size, number, distribution of second phase particles, as well as the size and morphology of thin strips grain of under-aged 7N01 aluminum alloy plate were almost the same. However, the under-aged 7N01 aluminum alloy plate has a significant strain-hardening effect after pre-tensile at room temperature, with the yield strength, tensile strength, and hardness increased from 181 MPa, 233 MPa, and 95 HV (without pre-tensile deformation) to 254 MPa, 271 MPa, and 117 HV (after 20% pre-tensile deformation), while the elongation decreased from 23.2% to 5.2%. Under the 175 MPa pulsating tensile load condition (stress ratio R = 0), the overall fatigue life of the under-aged 7N01 aluminum alloy plate first reduced, then prolonged, and then decreased as pre-tensile deformation increased. Without pre-tensile deformation, the fatigue life of under-aged 7N01 aluminum alloy plate is about 6.06 × 10⁵ cyc, and when prolonged by about 75%, it reaches about 1.06 × 10⁶ cyc after 5% pre-tensile deformation. However, the fatigue life of the under-aged 7N01 aluminum alloy plate is decreased to 4.21 × 10⁵ and 2.89 × 10⁵ cyc after 3% and 20% pre-tensile deformation, respectively. The evenly distributed high-density dislocations or dislocation cells resulted in 5%-16% pre-tensile deformation in the under-aged 7N01 aluminum alloy plate, which can prolong the fatigue life of the alloy plate by over 23%.