Interface axial evolution process and surface integrity improvement mechanism of aluminum hole burnishing

Hole burnishing serves as a highly efficient and economical technique for improving the fatigue performance of aluminum alloy load-bearing holes. However, the effectiveness of burnishing is limited by the presence of the critical burnishing depth (BD). This study employs aluminum alloy 7050 to explore approaches for increasing the critical BD by altering the shape of the contact geometry between the tool’s roller and the workpiece. By observing the hole geometry, surface roughness, surface morphology, hardness, residual stress, and fatigue life of the workpieces’ hole wall, the impact of the roller bottom shape on the burnishing effect was investigated. The results indicated that changes in the roller bottom shape affect the rate of normal-direction deformation (NDD) and the material deformation duration (MDD), thereby influencing the processing effect. By setting the chamfer radius at the bottom of the roller to 1.25 mm, 2.5 mm, and 5 mm, it was found that tools with a radius of 2.5 mm and 5 mm achieved a critical BD larger than the original tool with a radius of 1.25 mm. Furthermore, the tool with a 2.5 mm radius resulted in better surface roughness after burnishing, and the fatigue life was maximized with 0.1 mm BD and 2.5 mm radius, representing an increase of 119.8% compared to the unburnished hole.