Investigation Of Microstructure And Grain Refinement Mechanism About Surface Nanocrystallization Aluminium Alloy

Increasing interests have been focused on nanocrystalline (nc) materials during the past decade with the anticipation that their properties will be different from,and often superior to those of conventional coarse-grained materials. However,difficulties exist in obtaining "ideal" (i.e.,flaw-free,contamination-free,residual stress-free and with a sufficiently large sample size) nc samples by using the present preparation techniques. With increasing evidences of novel properties in nc materials,it is reasonable to propose to achieve surface modification by the generation of a nanostructured surface layer so that the overall properties and behavior of the material are significantly improved.A nanostructured surface layer has been successfully obtained in many material systems.Nevertheless,up to now,a clear scenery of microstructures and properties of the nanostructured surface layers,especially formation of nano sized crystallites from coarse polycrystals during plastic deformation,is still lacking. Therefore,understanding of the underlying mechanism for grain refinement by severe plastic straining is becoming more and more crucial.In this work,microstructural characteristic at different depths of the nanostructured surface layer in Al-Zn-Mg alloy sample induced by surface high energy shot peening(HESP) treatment was investigated by means of...