Multiple Laser Shock Processing Research Articles

Grain refinement of LY2 aluminum alloy induced by ultra-high plastic strain during multiple laser shock processing impacts

The plastic deformation behavior and the effects of the impact time on the LY2 aluminum (Al) alloy during multiple laser shock processing (LSP) impacts were investigated. The residual stress in the near-surface region was determined by X-ray diffraction. In addition, the micro-structural features of the hardening layer were characterized by scanning electron microscopy, optical microscopy and transmission electron microscopy. It was found that the micro-structure was obviously refined due to the ultra-high plastic strain induced by multiple LSP impacts. The minimum grain size in the top surface after multiple LSP impacts was about 100–200 nm. The grain refinement process after multiple LSP impacts can be described as follows: (i) the formation and development of dislocation lines in original grains; (ii) dislocation tangles (DTs) and the formation of dense dislocation walls (DDWs); (iii) transformation of DTs and DDWs into subgrain boundaries; and (iv) evolution of the continuous dynamic recrystallization in subgrain boundaries to refined grain boundaries.

3-D FEM simulation of laser shock processing

Laser shock processing is an innovative surface treatment technique similar to shot peening. It can impart compressive residual stresses in material for improving fatigue, corrosion and wear resistance of metals. FEM simulation is an effective method to predict mechanical effects induced in the material treated by laser shock processing. An analysis procedure including dynamic analysis performed by LS-DYNA and static analysis performed by ANSYS is presented in detail to attain the simulation of the single and multiple laser shock processing to predict the residual stress field and the surface deformation. History of the energies during dynamic analysis is analyzed and validated by the theoretical calculation. The predicted residual stress field for single laser shock processing is well correlated with the available experimental data and a homogeneous depression with little roughness modification in the action zone of the shock pressure is induced on the treated surface according to the simulation of surface deformation. Simulation of multiple laser shocks is also performed, which indicates that compressive residual stresses and plastically affected depth can be extensively increased and gradually reach the saturated state with the increase of laser shock number.