Microstructure evolution of AZ91D induced by high energy shot peening

A nanostructured surface layer was fabricated on a AZ91D magnesium alloy by using a high-energy shot peening(HESP). HESP induced structure along the depth of the treated sample surface layer was characterized by means of X-ray diffractometer (XRD), transmission electron microscope(TEM) and high resolution transmission electron microscope(HRTEM). The experimental results show that a deformed layer of about 50 μm has formed after HESP treatment and the average grain size increases from about 40 nm in the surface layer to about 200 nm at the depth of 40 μm. The surface nanocrystallization can realize intercoordination of the dislocations slipping and dynamic recrystallization. The nanocrystalline grains have stacking faults and dislocation in their interiors. The microhardness of the top surface is about triplicate that of the coarse-grained matrix.