| AZ31B magnesium alloy is in the category of biodegradable materials and has properties similar to human bones,so it is widely used in the field of transplantation of medical materials,However,the high corrosion rate and biocompatibility problems caused by entering the human body limit its application.Existing surface treatment methods,such as micro-arc oxidation,shot peening,laser fusion,etc.,have the risk of endangering biocompatibility and reducing mechanical properties when solving the above shortcomings.As one of the surface modification technologies,laser shock peening technology can introduce high-amplitude residual stress on the surface of the material,refine the surface structure,and can effectively improve the mechanical properties and corrosion resistance of the material.This subject takes AZ31 B magnesium alloy as the research object,uses laser shock peening technology for surface modification,and studies the influence of different pulse energy laser shock on the corrosion resistance and biocompatibility of AZ31 B magnesium alloy.The main research contents are as follows:(1)Through surface microstructure analysis,surface morphology and roughness analysis,microhardness and residual stress testing,the effect of laser shock peening with different pulse energy on the surface integrity of AZ31 B magnesium alloy was studied:Laser shock refines the surface structure,induces surface plastic deformation and strain hardening,increases surface roughness,and both increase with the increase of pulse energy.The OM results show that the surface grains of the sample are refined after laser shock,and the depth of the shock-affected layer increases with the increase of pulse energy.In the TEM observation,it is found that the crystal grains are nanosized after impact,and at the same time,a large number of twins and high-density dislocation entanglements are produced by laser shock peening.According to the EBSD grain size distribution,the grain sizes of LSP 2 J,LSP 3 J,and LSP 4 J are 4.370 ?m,3.865 ?m,and 3.062 ?m,respectively.Compared with the original material with a grain size of 12?m,it has been refined by 63.6%,67.8%,and 74.5%.XRD analysis found that the main diffraction peaks of the sample after impact were broadened and shifted to the left,the secondary diffraction peaks disappeared,and no new phases were produced,indicating that the grains were refined after impact,the microscopic strain increased,and the second phase solid solution phenomenon appeared.(2)Through the electrochemical corrosion test in 0.9 wt.% NaCl solution,the effect of laser shock strengthening with different pulse energy on the electrochemical corrosion performance of AZ31 B magnesium alloy was studied:After immersing for a long time,the AZ31 B magnesium alloy exhibits better corrosion resistance after laser shock peening.In the initial stage of immersion,the open circuit potential of the AR specimen and the pulse energy of 2 J,3 J,and 4 J specimens are-1.542 V,-1.562 V,-1.571 V and-1.583 V,respectively.After 24 hours of immersion,the open circuit potentials of the four groups of samples were-1.404 V,-1.482 V,-1.48 V and-1.470 V,respectively.The samples showed a low self-corrosion tendency after impact.Analyzing the impedance spectrum curve,it is found that the impedance value of the untreated sample continues to decrease.After the impact,the impedance spectrum of the sample decreases first and then increases with the immersion time.The accumulation of surface corrosion products to form a protective film can effectively slow down the corrosion rate.(3)The cytocompatibility test was carried out on the samples before and after impact,and the effect of laser shock peening on the cytocompatibility of AZ31 B magnesium alloy was studied:The observation results of cell survival rate and cell morphology show that laser shock-strengthening AZ31 B magnesium alloy has no toxic effect on the growth and reproduction of the cells on the surface,does not change the cell morphology,and shows a certain promotion effect on the cell survival rate under long-term culture.The larger the pulse energy,the stronger the promotion.When cultured for 7 days,the cell survival rate of the sample group after shock increased by 35.6% on average compared with the AR sample group.Laser shock peening makes the ? phase solid solution,and the content of surface Al and P elements increase with the increase of pulse energy,forming an aluminum-rich layer and a phosphorus-rich layer on the surface of the sample,and the corrosion resistance and cell compatibility are improved.In summary,the research in this article provides a theoretical and experimental basis for laser shock peening of AZ31 B magnesium alloy to improve corrosion resistance and cytocompatibility. |
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