Surface Conditions after LASER Shock Peening of Steel and Aluminum Alloys Using Ultrafast Laser Pulses

Laser shock peening (LSP) is a mechanical surface treatment process to modify near-surface material properties. Compared to conventional shot peening (SP) the process parameters can be finely adjusted with greater precision and a higher penetration depth of compressive residual stresses could be reached. However, high process times of LSP leads to high production costs. In this study, ultrafast LSP (U-LSP) with an ultrafast laser source (pulse time in the picosecond range) was applied on specimens made of X5CrNiCu15-5 and AlZnMgCu1.5. The surface characteristics (surface roughness) and surface-near properties (microstructure, residual stresses, and phase composition) were compared to the as-delivered condition, to conventional laser shock peening (C-LSP), and to SP, whereas metallographic analyses and X-ray and synchrotron radiation techniques were used. The process time was significantly lower via U-LSP compared to C-LSP. For X5CrNiCu15-5, no significant compressive residual stresses were induced via U-LSP. However, for AlZnMgCu1.5, similar compressive residual stresses were reached via C-LSP and U-LSP; however, with a lower penetration depth. A change in the phase portions in the surface layer of X5CrNiCu15-5 after C-LSP compared to SP were determined.

Automated summary

Laser shock peening (LSP) is a mechanical surface treatment process that can modify near-surface material properties. Compared to conventional shot peening (SP), LSP allows for more precise adjustment of process parameters and achieves greater penetration depth of compressive residual stresses. However, the high process times of LSP result in high production costs. This study explores the application of ultrafast LSP (U-LSP) using an ultrafast laser source on different materials. The results show that U-LSP significantly reduces process time and can achieve similar compressive residual stresses compared to conventional laser shock peening (C-LSP) in certain cases.