Fatigue failure analysis and life prediction of forged 6061 aluminum alloy wheel hubs based on precipitate size effects and multiaxial stress modeling

Abstract

Forged aluminum alloy wheel hubs are susceptible to premature fatigue failure under multiaxial loading in automotive applications. This study aims to address these challenges by developing a fatigue life prediction model that incorporates the crack initiation mechanisms specific to forged 6061 aluminum alloy. The microstructure and mechanical properties of the material were thoroughly characterized, revealing that cracks typically initiate at surface defects and precipitate-matrix interfaces. The grain sizes are refined to 50–100 μm, and a uniform precipitate distribution is obtained by dynamic recrystallization during the spinning process, thereby enhancing the strength–ductility synergy. Fractographic analysis revealed crack initiation at surface defects or precipitate–matrix interfaces. A three-stage failure mechanism “precipitate size–interfacial stress–microvoid evolution” is proposed: (I) stress concentration caused by precipitates exceeding the critical size, (Ⅱ) debonding driven by interfacial stress, and (Ⅲ) crack nucleation induced by microvoid evolution. To improve the accuracy of fatigue life predictions, a modified Basquin equation is combined with the critical plane method, integrating a fatigue stress concentration index (FSCI) and a life sensitivity coefficient (η = 0.085). The model demonstrates high predictive accuracy, with a maximum deviation of −1.8 % and an average error of less than 2 % compared to simulation results. The FSCI-based model gives a reliable prediction on the fatigue life exceeding 10⁷ cycles at operational stress amplitude below 140 MPa.