预拉伸形变对Mg-Zn-Sr-Zr-Mn合金降解行为的影响

Effect of pre-stretching deformation on degradation of Mg-Zn-Sr-Zr-Mn alloy

摘要:

镁合金具有优异的生物相容性和独特降解性，但其在生理环境中的耐蚀性能较差，严重制约了其在临床应用中的发展。本文使用预拉伸工艺制备Mg-Zn-Sr-Zr-Mn新型镁合金，通过XRD（X-ray Diffraction）、OM（Optical Microscopy）和SEM（Scanning Electron Microscopy）探究预拉伸形变量与显微组织、腐蚀速率和膜层形貌间的关系。结果表明：随预拉伸形变量的增大（2%、4%、6%），合金晶粒尺寸被逐渐拉长，孪晶数目逐渐增多，析出相离散程度逐渐增大。4%预拉伸合金由于适量孪晶的出现及析出相离散程度的增大，增加了电偶腐蚀形核点位，加速了合金表面均匀氧化产物的快速产生，增大了合金极化电阻阻值（729.4 Ω·cm-2）；三种预拉伸合金电化学（0.39→0.25→0.74 mm·y-1）及失重速率（2.85→1.83→5.88 mm·y-1）均呈现先降低后升高的趋势。4%预拉伸合金具有较高的耐蚀性证明适当的预拉伸变形提高界面析出相的连续性，阻碍腐蚀进程，对合金腐蚀性能起到积极作用。而当预拉伸形变量继续增加，产生大量位错，创造氢扩散路径，有利于氢富集，导致合金耐蚀性下降。此外，适当的预拉伸形变通过改变残余应力的重新分布，提高腐蚀均匀性，同时提高膜层致密性与连续性，延缓腐蚀进程。

Abstract:

Magnesium alloys own excellent biocompatibilities and unique degradation characteristics. However, the poor corrosion resistance in physiological environment seriously restricted its development in clinical applications. In this study, Mg-Zn-Sr-Zr-Mn alloys were prepared by pre-tensile process. XRD (X-ray diffraction), OM (optical microscopy) and SEM (scanning electron microscopy) were used to investigate the relationship between the pre-tensile type variables and the microstructure, corrosion rate and film layer morphology. The results showed that with the increase deformation of pre-stretching, the grain sizes were gradually elongated, the numbers of twins were increased, and the dispersion degrees of precipitated phases were gradually increased. The corrosion rate of the three pre-stretching alloys in electrochemical (0.39→0.25 →0.74mm·y-1) and weight-loss (2.85→1.83→5.88mm·y-1) were both decreased firstly and then increased. Therein, the 4% pre-stretching alloy has high corrosion resistance, which indicated that appropriate pre-tensile deformation could improve the continuity of the precipitated phase at the interface, hinder the corrosion process, and play a positive role in the corrosion properties of the alloys. However, when the pre-tensile deformation continues to increase, a large number of dislocations will be generated and hydrogen diffusion path will be created, which was conducive to hydrogen enrichment and leads to the decrease of corrosion resistance. Moreover, appropriate pre-tensile deformation could improve the corrosion uniformity, densification and continuity of the film-layer, and delay the corrosion process by changing the redistribution of residual-stress.