The pretreatment processes of direct electroless nickel plating on AZ91D magnesium alloy were studied in this paper.The surface morphology and surface composition after pretreatment processes,and the phase composition of nickel coating were analyzed by Optical Microscope,SEM and Energy Spectrometer and so on.And the alkali washing process,the pickling process and the activating process were defined.Results show that in the conditions of pickling in CrO3 125 g/L and HNO3(68%) 110 mL/L solution,and actvating ...