Reconstruction Mechanism of Surface Integrity for Laser Additive Manufactured 316 L Stainless Steel Subjected to Ultrasonic Surface Rolling Process: Numerical Simulation and Experimental Verification

The ultrasonic surface rolling process (USRP) is a strengthening process to improve the surface properties and enhance the mechanical performances of metal materials based on severe plastic deformation and high strain rates. In this study, a three-dimensional numerical model was established to investigate the reconstruction mechanism of surface integrity for the laser additive manufactured 316 L stainless steel (LAMed 316 L) subjected to USRP. The accuracy of the USRP model was confirmed by experimental results of residual stress, microhardness, and surface roughness. The results showed that the static pressure played a crucial role in causing the plastic deformation and strain hardening, followed by the decreased surface roughness, improved microhardness, and induced compressive residual stresses. The introduction of ultrasonic high-frequency impact with the smaller force contributed to the high strain rate plastic deformation and the surface tensile stress release, and improved the plastic deformation efficiency greatly. The reconstructed surface integrity of LAMed 316 L was attributed to the plastic strain, strain hardening, and grain refinement.

Graphical Abstract