Microplastic deformation activating residual stress relief for Al alloy

•The relationship between residual stress and microstructure during thermal-vibratory process is systematically investigated.•The reduced residual stress at the atomic scale mainly comes from the grain rather than the GB.•The phenomenon of micro-plastic deformation controls residual stress relief is revealed.•The effects of the TVSR amplitude, temperature, and initial residual stress on residual stress relief rate is predicted.