| WANG Wenquan,ZHAO Xintian,YU Wenhui,ZHENG Hongyu,WANG Zongshen.Effect of Laser Shock Peening on Surface Integrity of Additively Manufactured Mg Alloy[J],54(11):173-183 |
| Effect of Laser Shock Peening on Surface Integrity of Additively Manufactured Mg Alloy |
| Received:December 09, 2024 Revised:April 10, 2025 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.11.014 |
| KeyWord:laser shock peening selective laser melting additive manufacturing AZ91 Mg alloy surface integrity defect regulation |
| Author | Institution |
| WANG Wenquan |
Centre for Advanced Laser Manufacturing School of Mechanical Engineering, Shandong University of Technology, Shandong Zibo , China |
| ZHAO Xintian |
Centre for Advanced Laser Manufacturing School of Mechanical Engineering, Shandong University of Technology, Shandong Zibo , China |
| YU Wenhui |
Centre for Advanced Laser Manufacturing School of Mechanical Engineering, Shandong University of Technology, Shandong Zibo , China |
| ZHENG Hongyu |
Centre for Advanced Laser Manufacturing School of Mechanical Engineering, Shandong University of Technology, Shandong Zibo , China |
| WANG Zongshen |
Centre for Advanced Laser Manufacturing School of Mechanical Engineering, Shandong University of Technology, Shandong Zibo , China |
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| Abstract: |
| Mg alloys have drawn considerable attention in the biomedical field due to their superior biological properties, ultra-low density close to human bone, and no stress shielding phenomenon. Owing to its capability of fabricating geometrically complex structures, additive manufacturing has provided unprecedented opportunities to produce biodegradable metallic implants especially using Mg alloys. However, defects such as porosity, residual tensile stress and anisotropy resulted from the high cooling rates, high temperature gradients and multiple transient cycles greatly limit further applications of Mg alloys produced by additive manufacturing. Laser shock peening (LSP) stands as an innovative surface treatment technique by inducing intense plastic deformation and residual compressive stress at the material surface with a significant affecting depth. Thus, in this work, to improve the surface integrity and expand the application range of additively manufactured Mg alloys, the surface of AZ91 Mg alloy sheets prepared by selective laser melting (SLM) is creatively post-treated by employing different number of LSP and the effect of impact number on surface integrity of the alloy is investigated. The surface morphology and roughness, microhardness and residual stress level of additively manufactured Mg alloys are evaluated by scanning electron microscope, laser scanning confocal microscope, microhardness measurement and residual stress test, respectively. The evolution of microstructure and porosity defects of the alloy samples are analyzed by optical microscope, electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD). The results show that, after LSP, the unmelted particles and their agglomeration phenomenon on the sample surface are evidently reduced and the surface tends to be flat and smooth. The surface roughness is decreased with the increase of impact number from the initial 15.47 μm to 8.87 μm after 4 impacts by about 43%. The surface microhardness is increased from 103.04HV to 160.81HV with an increase of about 56%. The cross-sectional microhardness exhibits a gradient distribution along the depth direction, which is the most significant after 2 impacts, and the affecting depth is around 400 μm. The residual compressive stress is raised from the initial 3.52 MPa to 24.02 MPa. Meanwhile, the additively manufactured samples experience a prominent decrease in the number of internal porosity defects and the porosity morphology is evidently changed after LSP. Besides, gradient microstructure and grain refinement near the sample surface is introduced. The average grain size of the sample subsurface is refined from the initial 5.36 μm to 1.68 μm after 4 impacts, and a crystalline size of about 255 nm estimated by XRD results is finally obtained. In conclusion, the surface integrity of the additively manufactured Mg alloy samples is effectively improved by the combined action of the mechanical effect and the thermal effect generated by the laser-induced high-temperature and high-pressure plasma shock wave during LSP. The effect of LSP is gradually promoted by increasing impact number whereas basically the optimum results are achieved after 2 impacts and further repetition brings no more benefits. The availability and efficiency of LSP as a promising post-treatment technique utilized for improving surface integrity and related properties as well as enhancing their performance of additively manufactured Mg alloys are innovatively tried and proved in this work. |
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