Ductility improvement of aluminum 1050A rolled sheet by a newly designed ball burnishing tool device

Abstract

Conventional ball burnishing processes using a roller or a ball pressed against round or small flat surfaces have long been used to improve hardness, fatigue strength, and wear resistance of mechanical parts by plastic deformation. However, the treatment of large flat surfaces using conventional techniques is rarely considered because of its time consumption. In the present work, the optimal burnishing parameters of rolled sheets of aluminum 1050A are determined by means of a newly developed burnishing tool device especially designed to treat large flat surfaces with orders of magnitude reduction in burnishing time. Experiments were designed and performed on a machining center based on response surface methodology with central composite design. The burnished specimens were then tested to find the burnishing condition under which ductility was improved. This study has resulted in significant new insights into the effect of burnishing on the surface quality and workpiece properties of aluminum 1050A plates. A second-order mathematical model, validated using data obtained from atomic force microscopy, was developed to predict the surface roughness as functions of speed, force, and feed rate. The results indicate that burnishing of aluminum 1050A plates improves its ductility, but not its micro-hardness. Following the various burnishing conditions, the micro-hardness measurements range from 40 to 43 HV (50 g), indicating that there is little or no hardening. Although a moderate effect with varied degrees is found on the surface roughness as functions of the investigated parameters, the burnishing force has a significant effect on ductility. The results also indicate that lower values of roughness do not guarantee better ductility for aluminum 1050A plates. Furthermore, the effect of the burnishing loads on the residual stresses was found to depend on the feed direction.