Microstructure and Corrosion Properties of ZnMgMn Alloy with Different Content of Rare Earth Gd Element AITranslate

［1］Hernández-Escobar D，Champagne S，Yilmazer H，Dikici B，Boehlert C J，Hermawan H. Current status and perspectives of zinc-based absorbable alloys for biomedical applications ［J］. Acta Biomaterialia，2019，97：1.

［2］Li H F，Zheng Y F，Qin L. Progress of biodegradable metals ［J］. Progress in Natural Science：Materials International，2014，24（5）：414.

［3］（郑玉峰，杨宏韬. 血管支架用可降解金属研究进展 ［J］. 金属学报，2017，53（10）：1227.）

Y F Zheng，H T Yang. Research progress in biodegradable metals for stent application ［J］. Acta Metallurgica Sinica，2017，53（10）：1227.

［4］Bowen P K，Guillory II R G，Shearier E R，Seitz J M，Drelich J，Bocks M，Zhao F，Goldman J. Metallic zinc exhibits optimal biocompatibility for bioabsorbable endovascular stents ［J］. Materials Science & Engineering C，2015，56：467.

［5］Li G N，Yang H T，Zheng Y F，Chen X H，Yang J A，Zhu D H，Ruan L Q，Takashima K. Challenges in the use of zinc and its alloys as biodegradable metals：perspective from biomechanical compatibility ［J］. Acta Biomaterialia，2019，97：23.

［6］（董广壮，张凯，涂浩，王建华，苏旭平. Si和La协同作用对ZZnAl4Y锌合金显微组织与力学性能的影响 ［J］. 稀有金属，2023，47（2）：236.）

G Z Dong，K Zhang，H Tu，J H Wang，X P Su. Microstructure and mechanical properties of ZZnAl4Y zinc alloy with synergistic effect of Si and La ［J］. Journal of Rare Metals，2023，47（2）：236.

［7］Dambatta M S，Izman S，Kumiawan D，Farahany S，Ya-haya B，Hermawan H. Influence of thermal treatment on microstructure，mechanical and degradation properties of Zn-3Mg alloy as potential biodegradable implant material ［J］. Materials & Design，2015，85：431.

［8］Huang H，Liu H，Wang L S，Li Y H，Solomon-Oshioke A，Jing Bai，Xue F，Jiang J H. A high-strength and biodegradable Zn-Mg alloy with refined ternary eutectic structure processed by ECAP ［J］. Acta Metallurgica Sinica，2020，33（9）：1191.

［9］Liu X W，Sun J K，Zhou F Y，Yang Y H，Chang R C，Qiu K J，Pu Z J，Li L，Zheng Y F. Micro-alloying with Mn in Zn-Mg alloy for future biodegradable metals application ［J］. Materials & Design，2016，94：95.

［10］Miao H G，Huang H，Shi Y J，Zhang H，Pei J，Yuan G Y. Effects of solution treatment before extrusion on the microstructure，mechanical properties and corrosion of Mg-Zn-Gd alloy in vitro ［J］. Corrosion Science，2017，122：90.

［11］Chen J X，Tan L L，Yu X M，Yang K. Effect of minor content of Gd on the mechanical and degradable properties of as-cast Mg-2Zn-xGd-0.5Zr alloys ［J］. Journal of Materials Science and Technology，2019，35（4）：503.

［12］（唐仁政，田荣璋. 二元相图及中间合金相晶体结构 ［M］. 长沙：中南大学出版社，2009. 1276.）

R Z Tang，R Z Tian. Binary Phase Diagram and Intermediate Alloy Phase Crystal Structure ［M］. Changsha：Central South University Press，2009. 1276.

［13］（李伟健. 医用可降解多孔锌镁合金的制备及性能研究 ［D］. 太原：太原理工大学，2019. 1.）

W J Li. Preparation and Study on Properties of Medically Degradable Porous Zinc-Magnesium Alloy ［D］. Taiyuan：Taiyuan University of Technology，2019. 1.

［14］（汪磊. 新型Zn-Mg-Zr三元合金可降解生物材料的研究 ［D］. 南京：南京航空航天大学，2018. 1.）

L Wang. Novel Zn-Mg-Zr Ternary Alloys for Biodegradable Medical Implants ［D］. Nanjing：Nanjing University of Aeronautics and Astronautics，2018. 1.

［15］Gadelmawla E S，Koura M M，Maksoud T M A，Elewa I M，Soliman H H. Roughness parameters ［J］. Journal of Materials Processing Technology，2002，123（1）：133.

［16］（付晓雨，贾瑞灵，张贵龙，李丹，马文，郭锋. 稀土对AZ91镁合金腐蚀行为的影响 ［J］. 中国有色金属学报，2021，31（7）：1798.）

X Y Fu，R L Jia，G L Zhang，D Li，W Ma，F Guo. Effects of rare earths on corrosion behavior of AZ91 Mg alloy ［J］. The Chinese Journal of Nonferrous Metals，2021，31（7）：1798.

［17］García-Mintegui C，Córdoba L C，Buxadera-Palomero J，Marquina A，Jiménez-Piqué E，Ginebra M P，Cortina J L，Pegueroles M. Zn-Mg and Zn-Cu alloys for stenting applications：from nanoscale mechanical characterization to in vitro degradation and biocompatibility ［J］. Bioactive Materials，2021，6（12）：4430.

［18］Bagha P S，Khaleghpanah S，Sheibani S，Khahbiz M，Zakeri A. Characterization of nanostructured biodegradable Zn-Mn alloy synthesized by mechanical alloying ［J］. Journal of Alloys and Compounds，2018，735：1319.

［19］（李妍. Zn-Ag-Zr系可降解生物医用锌合金的制备及性能评价 ［D］. 广州：暨南大学，2017. 1.）

Y Li. Preparation and Performance Evaluation of Zn-Ag-Zr Biodegradable Biomedical Zinc Alloy ［D］. Guangzhou：Jinan University，2017. 1.

［20］（郭浦山. 新型可降解生物医用Zn-Sn及Zn-Zr合金的组织及性能研究 ［D］. 太原：太原理工大学，2017. 1.）

P S Guo. Study on Microstructure and Properties of New Biodegradable Biomedical Zn-Sn and Zn-Zr Alloys ［D］. Taiyuan：Taiyuan University of Technology，2017. 1.

Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23060003

Chinese Library Classification Number:TG146.2

Citation Information:

Zinc and its alloys are expected to become new generation of biodegradable metal materials，due to excellent biocompatibility and moderate degradation rates. The strength of pure zinc is about 20 MPa，which cannot meet the mechanical performance requirements of biological implant materials. However，alloying of zinc can greatly improve its mechanical properties To ensure the synergy of the mechanical properties and corrosive properties of Zn alloy，the mechanical properties and corrosion resistance of ZnMgMn alloy are improved by adding different amounts of Gd. Gd and Zn are both closely arranged hexagonal structures with heterogeneous nucleation conditions，which can refine the grain size of Zn alloy and improve its mechanical properties. The research on rare earth Gd in degradable alloys mainly focuses on degradable Mg alloys，and there is less research on degradable Zn alloys. It is very important to study the effect of Gd on the microstructure of ZnMgMn alloy and the electrochemical corrosion behavior and corrosion mechanism in simulated body fluid. The as-cast Zn-6Mg-0.5Mn-xGd （x=0，0.3，0.6，0.9；%，mass fraction） alloys were prepared by vacuum casting in this study. The phase and microstructure of the as-cast Zn-6Mg-0.5Mn-xGd alloys were studied using X-ray diffraction （XRD），optical microscope （OM），and scanning electron microscope （SEM）. The electrochemical properties of Zn-6Mg-0.5Mn-xGd alloys in simulated body fluid （SBF） solution were tested by the type PAR2273 electrochemical workstation，corrosion morphology and corrosion products of the alloys were tested by OM，XRD，SEM，and energy dispersive spectrometer （EDS）. The results showed that the as-cast Zn-6Mg-0.5Mn-xGd alloys were mainly composed of α-Zn phase，Mg₂Zn₁₁ phase，MgZn₂ phase and MnZn₁₃ phase. After adding the rare-earth Gd，the alloy produced a GdZn₁₂ phase. GdZn₁₂ phase was easily present α-precipitation and enrichment near the Zn phase. With the increasing of Gd，the alloy communist crystal organization was changed from divorced common crystal to laminar shape. The rod-shaped α-Zn phase gradually transformed into a spherical shape in the alloy，and Mg₂Zn₁₁ phase transformed into an equiaxed crystal with the addition of Gd element. MnZn₁₃ phase mainly precipitated as a dispersed phase in the eutectic structure layer，playing a dispersion strengthening role in the alloy. The alloy was passivated in SBF with the addition of rare earth Gd element. The average corrosion depth of Zn-6Mg-0.5Mn was 2.225 μm，and the deepest corrosion reached 24.448 μm. With the addition of Gd element，the corrosion resistance of the sample was significantly improved. When the Gd content was 0.6%，the corrosion resistance of the alloy was most significantly improved，with an average corrosion depth of 0.931 μm and the deepest corrosion reached 18.868 μm for Zn-6Mg-0.5Mn-0.6Gd alloy. When the Gd content was 0.6%，the highest self-corrosion potential was –927.277 mV，the lowest self-corrosion current density was 9.91 μA‧cm^-2，the largest charge transfer resistance was 1310 Ω·cm². The addition of rare earth Gd elements had no obvious effect on the composition of corrosion products. The corrosion products mainly composed of zinc （magnesium） oxide and zinc （calcium） phosphate. These products had excellent biocompatibility and could be completely absorbed and degraded by the human body. The addition of Gd element caused passivation of Zn-6Mg-0.5Mn-xGd alloy in SBF，resulting in a more obvious passivation zone in the Tafel curve，improved the corrosion performance of the alloy in SBF. On the other hand，the addition of Gd element homogenized the alloy structure，improved the distribution of phases in the alloy，and thus enhanced the corrosion resistance of the alloy. As the addition of Gd element exceeded 0.6%，the self-corrosion potential of Zn-6Mg-0.5Mn-0.9Gd alloy shifted negatively，and the self-corrosion current density increased. It was the reason that excessive addition of Gd element，which precipitated more second phases in the alloy，increased the potential difference in the alloy and caused electrochemical corrosion of Zn-6Mg-0.5Mn-0.9Gd alloy. After immersed in SBF for 21 d，the surface of Zn-6Mg-0.5Mn-0.6Gd alloy underwent corrosion，but the cracking phenomenon between grain boundaries was significantly improved. This indicated that the addition of Gd elements could improve the mechanical stability of the alloy during use. At the same time，there was no serious enrichment of corrosion products on the alloy surface，and the accelerated corrosion of the alloy could be delayed to a certain extent. At the initial stage of immersion，the surface of the alloy sample came into contact with the simulated body fluid to form a corrosive primary cell. Zn-6Mg-0.5Mn-xGd alloy acted as anode and underwent oxidation reaction with the solution，forming ZnO or Zn（OH）₂ on the surface. The cathode underwent oxygen absorption reduction reaction. These products were unstable and dissolve in the simulated body fluid，causing the alloy to continue to oxidize and dissolve. As the reaction progresses，the solution reached saturation and a solid film began to form，resulting in a gradual decrease in corrosion rate. With the prolongation of immersion time，Ca²⁺ in the solution reacted with weak acid ions （HCO₃^-，HPO₄^2-） through diffusion，and produced insoluble products in the supersaturated solution layer. These insoluble products gradually adhered to the oxide layer，forming a white spherical corrosion layer on the surface，and the corrosion rate further decreased. As the reaction progresses，the thickness of the passivation film increased. The film with a certain thickness would crack，because of the different thermal expansion properties between the passivation film and the alloy. There were network cracks in the passivation film layer，and cracking of the film could lead to surface redissolution. When the formation and cracking of the film reached a dynamic equilibrium，the corrosion of alloy would maintain a certain rate.