轧制形变量对Mg-Zn-Sr-Zr-Mn合金组织特征及降解性能的影响

Effect of Rolling Shape Variation on Microstructure Characteristics and Degradation Performance for Mg-Zn-Sr-Zr-Mn Alloys

摘要:

镁合金作为“新型可降解医用植入金属材料”在骨移植/血管支撑等医用领域具备巨大的发展潜力。然而，选择性溶解和偶发性氢聚集仍是影响镁合金临床应用的关键因素。在本研究中，采用光学显微镜（OM）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）、静态浸泡及动电位电化学测试等手段，深入探究轧制形变量的改变所诱导的显微组织以及膜层结构变化对热轧镁合金在生理环境中降解性能的影响机制。结果表明:不同轧制形变量镁合金的降解产物层均主要由Mg(OH)2、MgCO3、CaHPO4以及HA所组成。随着轧制形变量的增大，Mg-Zn-Sr-Zr-Mn合金的组织结构逐渐变的均匀，降解速率由1.03 mm·y-1降至0.24 mm·y-1。这是由于随轧制形变量的增大，基体晶粒显著细化，导致更多晶界的产生，阻碍腐蚀裂纹的扩展，并在腐蚀介质侵蚀过程中起到屏障作用。此外，轧制形变量的增大使合金中的第二相破碎以及弥散分布，降低了合金内部电偶腐蚀密度和强度，促进腐蚀的均匀发生，减少点蚀坑的产生。最后，热轧能改善腐蚀膜层的缺陷，在为合金表面提供更多的氧化膜形核点位的同时，还可以减少氧化膜的开裂，其致密性及稳定性随轧制形变量的增大而大幅度提升，进一步减缓了腐蚀离子的渗透。

Abstract:

As a new degradable metal material for medical implantation, magnesium alloy has great development potential in medical fields such as bone transplantation and vascular support. However, selective dissolution and accidental hydrogen accumulation are still the key factors affecting the clinical application of magnesium alloys. In this study, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), static immersion and potentiodynamic electrochemical test were used to explore the influence mechanism of microstructure and film structure changes induced by the change of rolling shape variable on the degradation performance of hot-rolled magnesium alloy in physiological environment. The results show that the degradation product layers of magnesium alloys with different rolling shape variables are mainly composed of Mg(OH)2, MgCO3, CaHPO4 and HA. With the increase of rolling shape variable, the microstructure of Mg-Zn-Sr-Zr-Mn alloy becomes uniform gradually, and the degradation rate decreases from 1.03 mm?y-1 to 0.24 mm?y-1. This is because with the increase of rolling shape variable, the matrix grain is significantly refined, resulting in more grain boundaries, hindering the expansion of corrosion cracks, and acting as a barrier in the corrosion process of corrosive medium. In addition, with the increase of rolling shape variable, the second phase in the alloy is broken and dispersed, which reduces the density and intensity of galvanic corrosion in the alloy, promotes the uniform occurrence of corrosion and reduces the pitting pit. Finally, hot rolling can improve the defects of the corrosion film, provide more nucleation points for the oxide film on the surface of the alloy, and reduce the cracking of the oxide film. The compactness and stability of the oxide film are greatly improved with the increase of rolling shape variable, and further slow down the infiltration of corrosion ions.