The increase of microhardness of Al-Li alloy is due to grain refinement and work hardening. Large elongated
grains are refined into small grains on the surface layer after shot peening. During shot peening process, the surface
of the workpiece is continuously impacted by a number of shots, which causes the plastic deformation of surface of
the workpiece. Therefore, the surface layer has a surface hardening effect to improve the surface hardness and
wear resistance