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Orthogonal experiments were conducted to investigate the effects of parameters on surface integrity in milling 7055 aluminum alloy. In order to correlate metamorphic layer with thermal and mechanical phenomena developed during milling, milling force and temperature fields of machined surface were obtained with finite element method, while milling speed and feed per tooth were paid particular attention to study formation of metamorphic layer. Experiment results show that when milling speed, feed per tooth, milling depth, and milling width are 1100 m/min, 0.02 mm/z, 0.7 mm, and 6 mm, respectively, obtained surface roughness, surface residual stress in X direction, surface residual stress in Y direction, and surface micro-hardness are Ra 0.258 µm, −123 MPa, −137 MPa, and 193.76 HV0.025, respectively. From precision machining to rough machining, depth of compressive residual stress layer increases from 35 to 45 µm, and the depth of plastic deformation layer increases from 5 to 20 µm. Finally, the formation of metamorphic layer can be explained by thermo-mechanical coupling effects.

To study the effect of different milled surfaces on shot peening surface integrity (roughness, residual stress, hardness, and microstructure), research on the change of surface integrity is carried out using the same shot peening process for different milling surfaces of 7055-T77 aluminum alloy. Surface integrity measurements, fatigue fracture analysis, and fatigue life tests are conducted to reveal the effect of surface integrity on crack initiation and fatigue life. The results show that shot peening can reduce the dispersion and instability of surface integrity brought by milling processing, although it increases the surface roughness; the maximum residual compressive stress and depth of residual stress layer increase significantly after shot peening, and the residual stress and hardening distribution are very good; larger surface roughness and irregular surface scratches of milling samples before shot peening easily lead to cracks and gouges produced on shot peening surface.