Study on surface Enhancement mechanism and fretting fatigue behavior of casting aluminum alloy under acousto-electropulsing-stress synergistic strengthening

Abstract

Casting aluminum alloy faces challenges during service, such as micro defects, low surface hardness, and inadequate fretting fatigue performance. This study employs acousto-electropulsing-stress synergistic strengthening to construct a strengthened layer structure on the surface of casting aluminum alloy, characterized by “micro-defect healing + surface gradient nanostructure.” The results demonstrate that, compared to surface burnishing processing, electro-ultrasonic surface burnishing processing (EUSBP) increases the thickness of the fine-grained layer by 75 % and enhances the amplitude of surface residual compressive stress by 39.3 % while simultaneously achieving micro-defect healing in the surface layer. Through fretting fatigue tests, it is discovered that the fretting fatigue life of EUSBP specimens is significantly higher than that of burnished and original specimens. Fracture surface analysis and damage zone characterization indicate that EUSBP specimens exhibit the best crack propagation resistance and fretting damage resistance. Molecular dynamics simulations reveal that EUSBP specimens enhance their resistance to fretting fatigue damage by utilizing the nano-gradient grain structure to inhibit dislocation motion and reduce the influence range of plastic deformation during the fretting fatigue process, resulting in a reduction of damage depth in the fretting fatigue damage zone by more than 25 %.