In this study, ball burnishing processes of the holes drilled in Al 6013 and MS 58 materials were investigated. In the tests, three different deformation portion (0.03-0.06-0.09) were left for both materials. After ball burnishing process, the samples were examined for surface roughness, micro hardness and microstructure.
Figure A. Ball burnishing process and surface roughness measurementPurpose: In this study, it is aimed to improve the surface properties of the holes drilled in Al 6013 and MS 58 materials. For this, the ball burnishing process was applied to the inside of the hole. Thanks to this method, besides improving the surface properties, increasing the surface hardness is another purpose.Theory and Methods: After drilling, the hole enlargement process was applied to the samples. Hole sizes were obtained in three different diameters (Ø a: 7.86-7.80-7.74 mm) depending on the ball diameter used in process. Ball made of bearing steel with a diameter of 7.92 mm was used in the ball burnishing process. The process was done on a lathe to forward the ball linearly along the hole axis. The inside of the hole is oiled to minimize friction and facilitate plastic deformation. Ball burnishing process was applied to the holes. The roughness of the hole surfaces was measured after the specimens were cut. Average surface roughness value was found by measuring from three different regions. After the sanding and polishing process was applied to the samples, microstructure images were taken and micro hardness measurement was made.Results: Thanks to the ball burnishing process applied to the Al 6013 material, the surface roughness value (in the sample A1 with 0.03mm deformation portion) decreased from 1.42 µm to 0.12 µm. It was observed that the surface roughness value of 1.65 µm measured before the process decreased to 0.17 µm in the MS 58 sample. It has been determined that the micro hardness of the Al 6013 material is 129 HV and the hardness increases to 142 HV in the area close to the hole surface. It was observed that the hardness of MS 58 material, which was 150 HV at a distance of 300 µm, was 180 HV in the region close to the hole surface.
Conclusion:It has been determined that the roughness of the hole surfaces is considerably reduced by ball burnishing process and polishing the holes in both materials. Thanks to this process, the surface roughness of the Al 6013 material decreased by 91.5% and for the MS 58 material by 89.6%. In the zone where plastic deformation occurred, 10% hardness increase was achieved for Al 6013 material and 20% hardness increase was achieved for MS 58 material. Considering the grain structure and hardness increase relationship, it has been found that the small grain structure enables higher surface hardness to be obtained.