Investigation of damage accumulation in under-aged 7005 aluminum alloy sheet during high-cycle fatigue process
摘要
Fatigue fracture is the primary failure in aluminum alloy structural components, and it often occurs without early warning and causes significant losses. Understanding the evolution of microstructure and properties during fatigue process to avoid fatigue fracture accidents has attracted much attention recently. In this work, the configuration of precipitates, dislocations and other microstructural features in under-aged 7005 aluminum alloy sheet subjected to various tension-tension fatigue cycles with a load ratio of 0.1 and at the maximum stress 205 MPa, as well as the fatigue crack propagation paths were investigated, to reveal the fatigue damage accumulation behavior of the alloy sheet during fatigue process. As the number of fatigue loading cycles increased to 7 × 106 cycles, the size of matrix precipitates in the under-aged 7005 aluminum alloy sheet gradually increased. Concurrently, the dislocation density in the alloy matrix monotonically increased from 0.07 × 1014 to 11.16 × 1014 m−2. The mechanical properties of the alloy sheet underwent two stages as the number of fatigue loading cycles increased, a fatigue hardening stage and a fatigue stable stage. During the fatigue cyclic loading, the proliferating dislocations primarily accumulated at front of the dispersoid particles to form dislocation arrays. Subsequently, dislocations transition to accumulating at the grain boundaries, forming dislocation networks that intersected the grain boundaries at approximately 45° and enveloped the grains, which resulted in the fatigue damage in the alloy sheet, ultimately leading to an intergranular fatigue fracture. The present work revealed the main reason for the high-cycle fatigue fracture of the under-aged 7005 aluminum alloy sheet, and provided basic data and theoretical basis to improve the safety and reliability of high-speed train components.