Combining gradient structure and supersaturated solid solution to achieve superior mechanical properties in WE43 magnesium alloy

•Surface mechanical attrition treatment was employed to successfuly produce a gradient nanostructured layer on WE43 magnesium alloy.•High-resolution TEM was mainly performed to successfully dissect the refinement mechanisms of the gradient nanostructure.•A supersaturated solid solution is formed by re-dissolving the Mg3RE second phase into nanostructured α-Mg matrix phase in the gradient layer.•Gradient structure and supersaturated solid solution cooperatively contribute to the extraordinary mechanical properties.