微量CaO对Mg-2Zn-0.5Sr镁合金显微组织、力学性能及腐蚀性能的影响

Effect of trace CaO on microstructure, mechanical properties and corrosion behavior of Mg-2Zn-0.5Sr alloy

摘要:

本文主要研究了添加0.1 wt.% CaO和0.3 wt.% CaO对Mg-2Zn-0.5Sr显微组织、力学性能及腐蚀性能的影响。光学显微镜(OM)、X射线衍射仪(XRD)及电子探针显微分析仪(EPMA)分析了材料均匀化热处理后的显微组织和第二相的组成与分布,发现CaO颗粒的加入使Mg-2Zn-0.5Sr的晶粒尺寸明显细化,而且CaO颗粒机械地富集于晶界及晶粒内的第二相与基体之间。室温拉伸试验研究材料机械性能,CaO颗粒的加入可以提高材料强度,但添加0.1 wt.% CaO时材料的塑性降低,而添加0.3 wt.% CaO时材料的塑性也有所提高,延伸率达到10.9 ± 1.1%。Kokubo模拟体液中的动电位极化曲线表明添加CaO颗粒使腐蚀电位正移。浸泡失重实验表明Mg-2Zn-0.5Sr的平均腐蚀速率为7.55 mm/year,添加0.1 wt.% CaO时腐蚀速率降低大约18.3%,添加0.3 wt.% CaO时腐蚀速率增高大约52%。CaO颗粒对显微组织及机械性能的影响决定于晶粒细化和CaO颗粒在第二相与基体之间机械富集的综合影响,而其对生物腐蚀行为的影响主要决定于晶粒细化及CaO颗粒在溶液中反应对致密稳定CaHPO4保护膜生成的促进作用。Mg-2Zn-0.5Sr/0.1CaO表现出较高的强度和较佳的耐腐蚀性能,是生物医用材料中的一种较好选择。

Abstract:

Effect of the addition of trace CaO particles (0.1 and 0.3wt. %) into Mg-2Zn-0.5Sr on the microstructure, mechanical properties, and bio-corrosion behaviors was investigated. Microstructures and the composition and distribution of the second phases of Mg-2Zn-0.5Sr-xCaO composites (x=0, 0.1 and 0.3wt. %) were characterized by optical microscope (OM), X-ray diffraction (XRD), electron probe microanalyzer (EPMA), which indicated that the addition of CaO particles can lead to grain refinement and the CaO particles were mostly enriched between the second phases at grain boundaries and the α-Mg matrix. Results of mechanical properties investigated by tensile tests at room temperature show that the addition of CaO particles can improve the strength. However when adding 0.1 wt.% CaO particles, the plasticity decreases, but when adding 0.3 wt.% CaO particles, the plasticity increases. Electrochemical tests show that the corrosion potential (E_corr) of Mg-2Zn-0.5Sr/CaO composites significantly shifts toward a more positive direction when CaO particles were added into Mg-2Zn-0.5Sr. Immersion tests show that the average corrosion rate of Mg-2Zn-0.5Sr is 7.55 mm/year. And when adding 0.1 wt.% CaO, the corrosion rate decreases by about 18.3%, and when adding 0.1 wt.% CaO, the corrosion rate increases by about 52%. Both the microstructure and mechanical properties can be attributed to grain refinement and the mechanical bonding of CaO particles with the second phases and the α-Mg matrix. The bio-corrosion behaviors can be attributed to grain refinement and the formation of table and dense CaHPO₄ protective film due to the reaction of CaO.