Materials with a gradient microstructure after surface strengthening have received a lot of attention due to their excellent mechanical properties. This paper reviews the preparation of gradient microstructures

their effects on mechanical properties (strength-plasticity

work hardening

friction wear and fatigue properties). Firstly

the mechanism of gradient microstructure formation and preparation methods are summarised according to the different principles of process preparation. Secondly

recent progress in the study of the mechanical properties of gradient microstructures (strong plasticity

work hardening

friction wear) and the analysis of the enhancement mechanism are summarised

while the anomalous test phenomena are explained. The reasons for the improvement of low and high cycle fatigue properties of metallic materials are comprehensively analyzed from the aspects of the gradient microstructure and residual stresses formed after surface strengthening. Finally

some of the current problems faced by gradient microstructure metals and future research directions are pointed out.