Influence of ultrasonic surface rolling process on the microstructure and rotating-bending fatigue properties of 7075-T6 aluminum alloys

Abstract

Ultrasonic surface rolling process (USRP) has attracted significant attention in metal surface strengthening due to its ability to tailor microstructural features and enhance mechanical properties. However, its effects on aluminum alloys remain insufficiently understood. This study aims to produce 7075-T6 aluminum alloys with varying surface conditions by adjusting the static pressure during USRP. The influence of gradient hardness and residual stress on rotating-bending fatigue properties was investigated. The results reveal that USRP induces surface gradient layers characterized by work hardening, compressive residual stress, and a high density of dislocations. At a static pressure of 200 N, the surface hardness and residual compressive stress reach 167 HV and 560 MPa, respectively. Enhanced surface hardness inhibits fatigue crack initiation, while compressive residual stress and dislocation density delay crack propagation. Consequently, the fatigue life of the USRP-200 N sample reaches 7.9 × 10⁶ cycles under 300 MPa, approximately 100 times longer than that of the untreated alloy.