Abstract: Scanning electron beam surface alloying technology can improve the surface properties of aluminum alloy.Different content of Y₂O₃ and Ni mixed powders were coated onto the surface of 6061 aluminum alloy using a plasma thermal spraying technique for surface alloying treatment using a scanning electron beam. The change of microstructure, phase structure and hardness of the strengthened layer after surface alloying was studied, and the influence of rare earth Y₂O₃ content and electron beam process parameters on the microstructure and properties of the strengthened layer was discussed. The results show that the surface of the electron beam can be divided into alloying zone, heat affected zone and matrix zone. The microstructure of the alloying zone is mainly composed of YAl₃, AlNiY and Ni₁₇Y₂, with a maximum hardness of 396 HV0.2, which is six times than that of the matrix. The thermally affected zone is mainly composed of α-Al solid solution and Ni-Al compound phase, with a maximum hardness of 260 HV0.2, which is four times than that of the matrix.The phase structure of the matrix is mainly composed of α-Al and Mg₂Si reinforced phase. With the increase of rare earth Y₂O₃ content, the microstructure grains of the alloy layer are refined and the hardness is improved.The content of rare earth Y₂O₃ is 5%, and the degree of tissue refinement and hardness improvement are the most obvious. The microhardness of the strengthening layer increases first and then decreases with the increase of the beam flow, and decreases with the increase of the moving speed.When the electron beam flow is 10 mA and the moving speed is 10 mm/s, the grain height of microstructure of the strengthening layer is refined and the hardness is improved significantly.