关键词： Mg alloys   Second phase   Dynamic recrystallization   Particle-stimulated nucleation   Pinning effect  

摘要： Dynamic recrystallization (DRX) and the related phenomena take place during thermomechanical processing that furnishes the final microstructure of a product. The microstructure of most Mg alloys composed of Mg matrices and second-phase particles, which significantly affect the DRX behavior and the formation of final microstructure. In the present work, four specific and inter-related topics were investigated according to four typical ingot conditions (as-homogenized, as-cast, cast-aged, and homogenization-aged) before hot extrusion on Mg-6.0Zn-0.5Zr (ZK60) alloy: the effect of initial grain boundaries on the DRX nucleation, the role of primary particles on the particle-stimulated nucleation (PSN) effect, the effect of precipitates on DRX nucleation and grain boundary migration, and the influence of two types second-phase particles on DRX behavior. After extrusion, the average grain size of cast-aged ZK60 is the finest, which is refined from 20.5 to 2.8 mu m. With the grains significantly refined, the mechanical properties of the cast-aged ZK60 are improved. The tensile yield stress, ultimate tensile stress, fracture elongation, compressive yield stress, and tension-compression yield asymmetry of the cast-aged ZK60 are 261 MPa, 338 MPa, 26.9%, 252 MPa, and 0.97, respectively. The results show that initial grain boundaries have huge potential to promote DRX nucleation. Coarse particles distributed at grain boundaries accelerate grain boundary nucleation. And the ones distributed in the grains have significant PSN effect to promote DRX nucleation. The fine precipitates distributed at new grain boundaries produce a pinning effect on the migration of grain boundaries, which prevent the growth of DRX grains. The combination of fine initial grains, coarse particles, and fine precipitates generate the best grain refinement during the DRX process. Therefore, after hot extrusion, the ZK60 alloy with cast-aged state before extrusion exhibits fine microstructure and good mechan

关键词： Biomedical magnesium alloys   Corrosion protection   Cytocompatibility   Composite coatings   Synergistic effects  

摘要： Practical application of magnesium (Mg) alloys to bone fixation implants is hampered by the rapid degradation under the physiological conditions. Herein, a composite coating composed of poly(L-lactic acid) (PLLA) / (3-aminopropyl)triethoxysilane (APTES) / hydroxide nanosheets is produced on the Mg alloy by spin coating, immersion, and hydrothermal methods to enhance the corrosion resistance and cytocompatibility. The combination of the inner hydroxide nanosheets and middle APTES layer promotes the formation of strongly adhering and dense PLLA layer on the Mg alloy by increasing the active sites for chemical bonding and flexible physical interlocking. Electrochemical studies reveal decreased corrosion current densities from 1.3 +/- 0.4 x 10(-4) to 1.8 +/- 0.6 x 10(-9) A cm(-2) and increased pore resistance from 1.15 x 10(2) to 2.70 x 10(7) Omega cm(2) in the simulated body fluid (SBF). Propagation of corrosion along the horizontal (surface) and vertical (depth) directions after soaking in SBF for 7 days is retarded notably by the composite coating which is capable of mitigating dissolution of the Mg alloy by impeding electrolyte penetration and minimizing coating delamination. Furthermore, the attachment and viability of MC3T3-E1 pre-osteoblasts in vitro demonstrate the obviously enhanced cytocompatibility by the composite coating.

关键词： Magnesium AZ31   Strontium (Sr)   Fracture micro-mechanisms   In-situ characterization   Digital image correlation (DIC)   Anisotropy  

摘要： Micro specimens of hot-rolled AZ31 and AZ31 + 0.8 wt% Sr magnesium alloys were tensioned in the rolling direction, and fracture micro-mechanisms were studied by in-situ real-time optical observations, electron microscopy, and DIC analysis. In-situ observations indicated that strain localization on the microstructural shear bands developed during tension was responsible for the fracture of the AZ31 specimens. DIC analysis demonstrated a substantial strain heterogeneity in the AZ31 sample, with the most intense concentration on the tensioninduced shear bands. Neither rolling nor tension shear bands were observed in AZ31-Sr alloy. Instead, many cracks were formed on the specimen surface, whose propagation led to the final fracture. Compared to the AZ31 alloy, the Sr-containing AZ31 alloy experienced a more uniform strain distribution during deformation. Most of the twins inherited from the rolling process were perpendicular to the rolling direction, which were identified as the source of crack initiation, especially in the Sr-added alloy. Microstructural evidence showed that the contribution of precipitates in damage of Sr-added AZ31 alloy was higher than that in AZ31 alloy. However, cracks were mostly initiated from the twin boundaries, not the precipitate stringers. The variations of plastic anisotropy coefficient (R-value) were described as a function of applied strain using DIC analysis. It was found that incorporation of Sr into AZ31 alloy reduced its pronounced anisotropy.

关键词： Cryogenic deformation   Slip   Plasticity   Magnesium alloys   Electron backscattering diffraction (EBSD)  

摘要： The mechanical behaviours of magnesium alloy (WE43) at cryogenic temperatures are investigated. The significant improvement in both fracture strength (28%) and strain-to-failure (24%) at -196 ?C is observed when compression direction is normal to the extrusion direction, as benchmarked against room-temperature properties. This considerable improvement in strain-to-failure and strength at cryogenic temperature is attributed to unusual enhanced pyramidal slip.

关键词： Magnesium alloys   Precipitation   Grain boundary co-segregation   Recrystallization   Grain growth  

摘要： Alloying additions in magnesium can modify common basal textures during recrystallization based on their solid solubility and precipitation behavior. With a variety of tenable theories in the literature, a far greater understanding is required of how restricted growth due to drag effects and annealing texture formation are linked. In the current work, a complex magnesium alloy Mg-3Al-1Zn-0.3Ca (wt.%) with multiple substitutional elements was subjected to a combination of deformation and annealing treatments in order to examine how a variation of bulk solute concentrations would influence its segregation and precipitation behavior. The work focuses in particular on solute segregation to grain boundaries and demonstrates that the type and level of segregation play a key role in controlling the growth behavior in such a way that restricts preferential growth of grains with a basal texture. Deeper knowledge in this area can be expected to advance current alloy design strategies by tweaking the solute concentration in the solid solution through targeted heat treatments to result in the required amounts of second phase precipitation and grain boundary segregation. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Hexagonal close-packed (HCP) materials   Magnesium (Mg) alloys   Grain-size effect   Textural variability   Crystal Plasticity  

摘要： This work investigates the microstructure-property linkages in magnesium (Mg) with an emphasis on understanding interaction effects between the grain size, texture, and loading orientation. A single crystal plasticity framework endowed with experimentally informed micro Hall-Petch type relations for the activation thresholds for slip and twinning is adopted to resolve polycrystalline microstructures over a broad texture-grain size space. The macroscopic trends from the simulations corroborate with experiments. The synergistic effects of microstructural engineering on the micromechanical characteristics are mapped, which reveal their role in the emergent macroscopic behaviors. The simulations predict reduced extension twinning with grain size refinement even though the micro Hall-Petch coefficient for twinning is smaller than that for the non-basal slip modes. While grain refinement and textural weakening generally reduce the net plastic anisotropy and tension-compression asymmetry, the degree to which these macroscopic behaviors are tempered depends on the loading orientation. The results offer preliminary insight into the roles that texture and grain size may play in the damage behavior of engineered Mg microstructures. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Coating materials   Alcohols   Liquids   Alloys   Magnesium  

摘要： The application of magnesium alloys is seriously limited by their poor environmental adaptability. In this work, we report a robust superamphiphobic coating, which endows magnesium alloys with extraordinary environmental adaptability. The coating was fabricated on magnesium alloys by a facile, cost-effective, and scalable method, one-step particle-free spraying. The as-treated magnesium alloys show excellent superamphiphobicity with the static contact angles (CAs) of water, ethylene glycol, benzyl alcohol, and cyclohexanol droplets of 157.5 degrees, 155.1 degrees, 151.7 degrees, and 151.3 degrees, respectively. These samples also display small dynamic CAs (0 degrees for water and 10 degrees for ethylene glycol) and water super-repellency, which endow magnesium surfaces with droplet impact resistance, self-cleaning, and oil-resistance functions. The simulating environmental-adaptability tests demonstrate that the as-treated magnesium alloys can remain superamphiphobic under various mechanical, chemical, and physical damages including sand impact (>= 10 cycles), water impact (nu = 4.5 m.s(-1), 2 impacts.s(-1), 20 h), abrasion (1.0 kPa, 50 cycles), strong acid/alkaline solution (pH = 1-14), organic solvents immersion (ethylene glycol, n-hexane, >= 48 h), high temperature (200 degrees C, 72 h), and ultraviolet irradiation (lambda = 254 nm, 672 h). The natural environmental-adaptability tests in the acidic industrial atmosphere for 40 days further confirm the robustness of the as-treated magnesium alloys under harsh environments. This work not only provides a promising method for industrially fabricating environmental-adaptable coatings on metallic materials but also paves the way for the much wider applications of magnesium alloys.

关键词： 磷酸钙骨水泥   生物相容性   骨缺损   成骨作用  

摘要： 目的:评价新型磷酸钙骨水泥(calcium phosphate cement,CPC)的生物相容性以及成骨效果,为其进一步的临床应用提供实验数据。方法:选择新西兰大白兔30只,以其双后腿外侧髁(60个)为实验对象,随机分为CPC组、CPC+Bio-Oss组、Bio-Oss组和空白对照组4组,在兔双侧后腿外侧髁制造直径6 mm、深7 mm的骨缺损模型,按照组别分别植入CPC、Bio-Oss、CPC+Bio-Oss混合物(CPC与Bio-Oss骨粉质量比为4∶1)。实验动物分别在手术第4周、第12周、第24周处死,取骨缺损周围组织,HE染色进行组织学评价,并计算新骨生成率(bone ingrowth fraction,BIF);利用免疫组织化学染色,计算阳性区域平均光密度(mean optical density,MOD),检测术后第4周各组样本BMP-2和COL-Ⅰ的表达情况,评价各组样本在不同时间点的骨愈合情况。结果:HE染色发现,在相同时间点,与空白对照组相比,CPC组、CPC+Bio-Oss组、Bio-Oss组的BIF值明显较高(P<0.01),其中,CPC组BIF低于Bio-Oss组和CPC+Bio-Oss组(P<0.01),CPC+Bio-Oss组与Bio-Oss组相比差异无统计学意义(P>0.05)。免疫组织化学染色结果显示,与空白对照组相比,CPC组BMP-2和COL-Ⅰ的MOD值较高,但低于Bio-Oss组和CPC+Bio-Oss组(P<0.01),CPC+Bio-Oss组BMP-2和COL-Ⅰ的MOD与Bio-Oss组相比差异无统计学意义(P>0.05)。结论:新型磷酸钙骨水泥具有良好的生物相容性,可以促进早期成骨,成骨效果稳定,长期有效。

关键词： 人工血管   动物模型建立   实验目的   生物相容性   在体实验   初步成果   模型的建立  

摘要： 近年来有不少国内研究人员致力于人工血管的研究,并取得初步成果为验证这类产品的生物相容性,大动物在体实验评价是必不可少的一环[2]。本实验目的是探索一种标准的降主动脉置换动物模型建立方法,为大口径人T.血管产品的动物在体评价提供实验基础。

关键词： 镁合金   有限元模拟   ECAP   模具拐角   模具圆心角  

摘要： 本文利用有限元软件对镁合金ECAP变形工艺进行了二维动态模拟,分析了不同模具拐角和模具圆心角镁合金试样的变形分布情况,并通过计算的方法研究了试样的变形均匀性。结果发现不同模具拐角时试样上、中、下部位的变形程度并不相同,中上部的变形程度要大于试样下部。计算得到,模具拐角为120°时,试样的变形相对均匀。而模具圆心角不同时,试样不同部位的变形各不相同。模具圆心角为52°时,试样整体变形较均匀。模具圆心角的大小还影响着死区的大小和试样的翘曲程度。为后续实验提供了可靠的理论依据。