The role of microstructural features on degradation and surface film development of a thermomechanically processed Mg-4Zn-0.5Ca-0.8Mn alloy has been investigated employing electrochemical studies, scanning electron microscopy and X-ray photoelectron spectroscopy. The specimen forged at 523 K temperature developed a coarse unimodal microstructure consisting of basal oriented grains, whereas the specimens forged at 623 K and 723 K temperatures exhibited bimodal microstructures containing randomly oriented fine grains and basal oriented coarse grains. The bimodal microstructures exerted higher resistance to corrosion compared to the unimodal microstructure in presence of a protective surface film. The optimum size distribution of fine and coarse grains as well as the prevalence of basal oriented grains led to the lowest anodic current density in the specimen forged at 623 K. The morphology of CaMgZn precipitates governed the cathodic kinetics by controlling the anode to cathode surface area ratio. Despite the specimen forged at 723 K comprised comparatively lower fraction of precipitates than at 623 K, the mesh-like precipitate morphology increased the effective cathodic surface area, leading to enhanced localised corrosion in the former specimen. Optimal microstructural features developed at 623 K forging temperature formed a well-protective surface film with lower Mg(OH) to MgO ratio, exhibiting distinctly high polarization resistance and superior cytocompatibility in terms of cell-proliferation and cell-differentiation.

中文翻译：

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热机械加工的新型镁合金增强的体外降解抗性和细胞相容性：深入了解微观结构属性的作用

采用电化学研究、扫描电子显微镜和 X 射线光电子能谱研究了微观结构特征对热机械加工的 Mg-4Zn-0.5Ca-0.8Mn 合金的降解和表面薄膜形成的作用。在 523 K 温度下锻造的样品形成了由基底取向晶粒组成的粗单峰显微组织，而在 623 K 和 723 K 温度下锻造的样品则表现出包含随机取向细晶粒和基底取向粗晶粒的双峰显微组织。在存在保护性表面膜的情况下，与单峰微结构相比，双峰微结构具有更高的耐腐蚀性。细晶粒和粗晶粒的最佳尺寸分布以及基底取向晶粒的普遍存在导致在 623 K 锻造的样品中阳极电流密度最低。CaMgZn 沉淀物的形态通过控制阳极到阴极表面积来控制阴极动力学比率。尽管在 723 K 下锻造的样品包含的析出物比例相对低于在 623 K 下锻造的样品，但网状沉淀物形态增加了有效阴极表面积，导致前一个样品中的局部腐蚀增强。在 623 K 锻造温度下形成的最佳微观结构特征形成了具有较低 Mg(OH)2 与 MgO 比率的良好保护性表面膜，在细胞增殖和细胞分化方面表现出明显高的极化电阻和优异的细胞相容性。