“…It is believed that grain refinement supplies a high density of nucleation sites for passive film formation [41,42] , which assists in the formation of a dense passive layer and a reduction in corrosion rate. The improved corrosion resistance behavior of the SMAT sample can be attributed to the rapid formation of a passive film on the grain refinement surface, which improves the chemical stability of the alloy by decreasing the diffusion of corrosive ions and the activity of charge carriers at the interface between solution and substrate [23,25,44,45] .…”