Performance evaluation of laser shock micro-patterning process on aluminum surface with various process parameters and loading schemes

In this study, a laser shock micro-patterning process was used to indirectly transfer laser energy to materials and to efficiently fabricate a microscale pattern array on the material surface. Various pressure transfer methods of laser shock waves were investigated and the optimal process condition was determined. The method of pressurizing the workpiece using the ablation layer was considered most appropriate for achieving the desired depth and homogeneity of the micro-patterns. The method of pressing the grid mold using the ablation layer was very effective in minimizing the shape deviation between the patterns. However, excessive deformation of this layer resulted in a large loss of depth. The method of creating a micro-pattern array through high-speed collisions of metal flyers with the workpiece played a minor role in the laser shock micro-patterning process. This resulted from the considerable energy loss and concentration of the impact in the central region of the flyer. The effect of the ablation-layer thickness and the insertion of the hyper-elastic material on the surface patterning performance was investigated. When a thin ablation layer was used, the energy loss was reduced and, hence, the depth of the micro-pattern increased. However, when the hyper-elastic material was inserted, reductions in the pressure transfer efficiency prevented improvements in the depth and homogeneity of the patterns. Hardness measurements of the patterned surface revealed that the hardness increased, due to the influence of the laser shock load, even in the region indirectly exposed to the laser shock wave. Furthermore, the hardness value increased with increasing depth of the micro-pattern.