Microstructure and Mechanical Properties of Wire + Arc Additively Manufactured Mild Steel by Welding with Trailing Hammer Peening

Abstract

Aiming at solving the problem of coarse grains and poor mechanical properties in weld by Wire Arc Additive Manufacture (WAAM), the welding with trailing hammer peening (WTHP) process is used. The stress state of weld after being processed by WTHP and the temperature distribution at different time are obtained by finite element simulation (FEM). The effects of different peening parameters on microstructure and mechanical properties of the weld are studied by using the light microscopy and Electron Back Scatter Diffraction (EBSD) for microcharacterization. The results show that the hardness of the near‐surface layer of weld is improved by 21.6% using WTHP. Ultimately, the yield strength of weld layer increases from 447 to 493.5 MPa, tensile strength from 560.8 to 661.9 MPa, while the ductility decreases from 32.9% to 21.1%. Three aspects of strengthening mechanisms for the near‐surface layer of the weld by WTHP are as follows: first, multiple high‐speed and high‐energy peening refines the grains of the near‐surface of the weld; second, the plastic deformation produced by hammer peening results in high‐density dislocation and deformation strengthening; and finally, the stress state of the weld is changed from the residual tensile stress to the residual compressive stress under the plastic deformation.