材料表面微纳形貌对血管细胞行为影响的研究综述

镁合金具有良好的生物相容性、优良的力学性能以及可完全降解的特点,是制备血管支架的理想材料。然而在支架植入初期,支架表面平滑肌细胞增殖速率超过内皮细胞增殖速率,导致支架内再狭窄的发生。近年来,在材料表面构筑微纳尺度形貌,通过调控血管内皮细胞和平滑肌细胞行为,实现支架表面快速内皮化成为一种新的研究思路。从基底材料、形貌特征、制备工艺、细胞种类以及实验结果等方面,系统地总结了近年来关于材料表面微纳形貌对血管细胞行为的影响。因为目前镁合金表面微纳形貌对血管细胞行为影响的报道尚少,从镁合金种类、形貌制备工艺、形貌特征以及形貌功能等方面详细整理了不同研究领域,在镁合金表面制备微纳形貌的相关研究。与此同时,分析了在镁基血管支架表面制备微纳尺度形貌用于实现支架表面快速内皮化研究所面临的挑战,并介绍了本课题组相关研究工作进展。

一种提高镁合金零部件抗火焰蔓延性的尺寸设计类判据

基于能量守恒定律提出了一种用于预测棒状镁合金样品火焰蔓延时间的判据,该判据表明火焰蔓延时间主要受合金材料和样品尺寸影响。控制体的初始温度和起燃温度以及样品的S/l_c比值(样品横截面面积/横截面周长)是火焰蔓延时间的决定性因素。火焰蔓延时间正比于ΔH(将单位质量的样品从初始温度加热到起燃温度所需的能量)和S/l_c比值,这在Mg-8.5Al-0.5Zn-0.2Mn、Mg-2.7Nd-0.4Zn-0.6Zr和Mg-4.0Y-3.3Nd-0.5Zr镁合金中得到验证。对于尺寸相同的样品,Mg-8.5Al-0.5Zn-0.2Mn合金样品有着最大的ΔH以及最长的火焰蔓延时间;对于材质、长度和横截面面积相同的样品,圆形横截面样品的S/lc比值最大,其抗火焰蔓延性能也最佳。

砂型铸造Mg-9Gd-3Y-0.5Zr合金的线收缩

研究铸件几何特征对砂型铸造Mg-9Gd-3Y-0.5Zr(VW93)合金线收缩的影响。利用3D扫描仪精确提取自由收缩和受阻收缩砂铸件的尺寸,并用于计算收缩系数。引入砂芯体积与铸件包络体积之比(γ)量化砂芯对铸件收缩的约束程度。通过分析自由收缩系数的统计分布和受阻收缩系数随γ的变化规律发现,VW93合金的自由收缩系数为1.96%,受阻收缩系数随γ的增大而线性减小,此关系为根据铸件几何结构预测VW93合金收缩率提供支持。

镁合金植酸化学转化膜研究进展

镁合金具有比强度高、密度低等优良的性能,目前正受到广泛关注,但镁合金本身的耐蚀性能差的特点限制了其应用。植酸转化膜对环境友好且具有良好的耐蚀性,在镁合金的防护上被视为铬酸盐转化膜的替代者之一。对目前镁合金植酸转化膜的研究进展进行了综述,对其成膜机理等进行了简要分析,并就其发展趋势进行了展望。

虚拟仿真实验教学研究现状和发展趋势--以液态成形为例

在线教学分为理论教学和实验教学,目前在线理论教学主要分为MOOC录播类教学和Zoom在线直播类教学。MOOC教学促进了优质教学资源的共享,很大程度上满足了学生自主学习的需求,是线下理论教学很好的补充。Zoom类在线直播教学与传统教学极为接近,同时也能突破地域的限制,在未来教学发展中具有很大的潜力。实验教学与理论教学一样有着重要的作用,目前很多线下实验教学开展困难,在线实验教学应运而生。虚拟仿真实验教学是在线实验教学的一个重要突破,解决了很多线下实验教学难以开展的问题,也是未来实验教学发展的一个重要方面。液态成形作为材料科学与工程专业的一个重要分支,其虚拟仿真实验教学可以解决高温、高污染环境下实验操作危险以及耗时长等问题。

固溶处理对铸造Mg-Gd-Ag-Zr合金的显微组织和室温拉伸力学性能的影响

采用不同的一级固溶和两级固溶工艺对Mg-xGd-2Ag-Zr(13≤x≤16,wt%)合金进行了固溶处理(T4)实验,采用OM、SEM显微组织分析以及室温拉伸力学性能测试,优化出Mg-xGd-2Ag-Zr合金的较佳的固溶工艺,并采用SEM和XRD对固溶态合金的相进行了研究。结果表明:对于GQ132K合金和G17K合金,采用一级固溶处理,共晶次生β相就可基本实现完全固溶。对于GQ142K、GQ152K、GQ162K合金而言,采用两级固溶处理工艺比采用一级固溶工艺更能取得较好的固溶效果,固溶后,残留Mg5(Gd,Ag)相的体积分数为0.30vol%~2.79vol%。优化出了Mg-xGd-2Ag-Zr系镁合金的最优固溶参数。经T4处理后,铸态Mg-xGd-2Ag-Zr合金的综合室温拉伸力学性能得到改善,其抗拉强度为295 MPa,屈服强度为157 MPa,而伸长率高达12.36%~17.52%。

Effects of processing parameters on microstructure of semi-solid slurry of AZ91D magnesium alloy prepared by gas bubbling

The semi-solid slurry of AZ91 D magnesium alloy was prepared by gas bubbling process.The effect of processing parameters,including gas flow rate,cooling rate and stirring end temperature,on microstructure of AZ91 D semi-solid slurry was investigated.With increasing the gas flow rate from 0 to 5 L/min,the average size of primary α-Mg particles decreases from 119.1 to77.2μm and the average shape factor increases continuously from 0.1 to 0.596.The formation of non-dendritic primary α-Mg particles during gas bubbling is the result of combined effects of dendrite fragmentation and copious nucleation.With increasing the cooling rate from 3.6 to 14.6℃/min,the average particle size of primary α-Mg phase decreases from 105.0 to 68.1μm while the average shape factor peaks at 9.1℃/min.Both high and low cooling rates can induce dendritic growth of primary α-Mg particles.Changing the stirring end temperature from 590 to 595℃ has little effect on the average size and shape factor of primary α-Mg particles in AZ91 D semi-solid slurry.The insensitivity of semi-solid microstructures to the stirring end temperature is attributed to the sufficient quantity of primary particles formed in the melt.

Effect of refining processes on inclusions and mechanical properties of cast Al-2Li-2Cu-0.2Zr alloy

The effect of different refining processes on inclusions and mechanical properties of cast Al-2Li-2Cu-0.2Zr alloy was investigated, including two-stage hexachloroethane (C2Cl6) refining process, two-stage rotating gas bubbling refining process and two-stage composite refining process. It was found that the two-stage composite refining process, which combined C2Cl6 and rotating gas bubbling, can significantly improve the melt purity and mechanical properties of cast Al-2Li-2Cu-0.2Zr alloy. Compared to the unrefined alloy, the volume fraction of gas porosity defects and slag inclusions decreased from 1.47% to 0.12%, and the yield strength, ultimate tensile strength and elongation of as-quenched alloy increased from 113 MPa,179 MPa and 3.9% to 142 MPa, 293 MPa and 18.1%, respectively. C2Cl6 was first utilized to degas and remove large size slag inclusions before lithium addition, and then the rotating gas bubbling was utilized to do the further degassing and remove the suspended fine inclusions after lithium addition. The two-stage composite refining process can take advantage of two methods and get the remarkable refining effect.

Microstructure and mechanical properties of squeeze-cast Al−5.0Mg−3.0Zn−1.0Cu alloys in solution-treated and aged conditions

The microstructure and mechanical properties at different depths of squeeze-cast,solution-treated and aged Al−5.0Mg−3.0Zn−1.0Cu alloy were investigated.For squeeze-cast alloy,from casting surface to interior,the grain size ofα(Al)matrix and width of T-Mg32(AlZnCu)49 phase increase significantly,while the volume fraction of T phase decreases.The related mechanical properties including ultimate tensile strength(UTS)and elongation decrease from 243.7 MPa and 2.3%to 217.9 MPa and 1.4%,respectively.After solution treatment at 470℃ for 36 h,T phase is dissolved into matrix,and the grain size increases so that the UTS and elongation from surface to interior are respectively reduced from 387.8 MPa and 18.6%to 348.9 MPa and 13.9%.After further peak-aging at 120℃ for 24 h,numerous G.P.II zone andη′phase precipitate in matrix.Consequently,UTS values of the surface and interior increase to 449.5 and 421.4 MPa,while elongation values decrease to 12.5%and 8.1%,respectively.

Effect of heat treatments on microstructure and mechanical properties of sand cast Al−2Li−2Cu−0.5Mg−0.2Sc−0.2Zr alloy

This study focused on modifying heat treatment schemes to enhance the mechanical properties of sand cast Al−2Li−2Cu−0.5Mg−0.2Sc−0.2Zr alloy.Different three-stage solution treatment schemes((460℃,32 h)+(520℃,24 h)+(530/540/550℃,4/12/24/32 h))and aging temperatures(125,175,225℃)were designed for comparison.The microstructure evolutions were analyzed by optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results showed that the three-stage solution treatment of(460℃,32 h)+(520℃,24 h)+(530℃,12 h)could dissolve most of the secondary phases.The TEM results illustrated that fineδ'(Al_(3)Li)particles were homogeneously distributed in the matrix after aging at 175℃for 8 h,accompanied by a small amount of lath-shaped S′(Al_(2)CuMg)and plate-like T_(1)(Al_(2)CuLi)phases.The best comprehensive properties of yield strength of 376 MPa,ultimate tensile strength of 458 MPa and elongation of 4.1%were obtained by the optimal heat treatment scheme((460℃,32 h)+(520℃,24 h)+(530℃,12 h)+(175℃,8 h)).

Microstructural evolution and mechanical performance of cast Mg−3Nd−0.2Zn−0.5Zr alloy with Y additions

This work investigated the effects of different Y additions(0,1.5,3.0 and 4.5 wt.%)on the microstructural evolution and mechanical performance of cast Mg−3Nd−0.2Zn−0.5Zr alloy.The results show that as the Y content increases,the key secondary phases in as-cast alloys change from the Mg_(12)Nd type to the Mg_(24)Y_(5) type.Meanwhile,the number density of Zn−Zr particles in the grains of as-quenched alloys gradually decreases.HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globularβ¢precipitates,leading to a significantly increased volume fraction and promoted precipitation kinetics ofβ¢precipitates,resulting in enhanced strength of the alloy.Tensile tests reveal that,with the addition of 4.5 wt.%Y,the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225°C under peak-aged conditions,respectively.

Effects of Mg content on microstructure and mechanical properties of low Zn-containing Al-xMg-3Zn-1Cu cast alloys

Effects of Mg content on the microstructure and mechanical properties of low Zn-containing Al−xMg−3Zn−1Cu cast alloys(x=3−5,wt.%)were investigated.As Mg content increased in the as-cast alloys,the grains were refined due to enhanced growth restriction,and the formation ofη-Mg(AlZnCu)_(2) and S-Al_(2)CuMg phases was inhibited while the formation of T-Mg_(32)(AlZnCu)_(49 )phase was promoted when Mg content exceeded 4 wt.%.The increase of Mg content encumbered the solution kinetics by increasing the size of eutectic phase but accelerated and enhanced the age-hardening through expediting precipitation kinetics and elevating the number density of the precipitates.As Mg content increased,the yield strength and tensile strength of the as-cast,solution-treated and peak-aged alloys were severally improved,while the elongation of the alloys decreased.The tensile strength and elongation of the peak-aged Al−5Mg−3Zn−1Cu alloy exceed 500 MPa and 5%,respectively.Precipitation strengthening implemented by T′precipitates is the predominant strengthening mechanism in the peak-aged alloys and is enhanced by increasing Mg content.

热处理对真空压铸NZ30K镁合金微观组织及力学性能的影响

使用光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)、硬度测试和拉伸性能测试等方法,研究了热处理对真空压铸NZ30K镁合金微观组织及力学性能的影响。结果表明:铸态合金的宏观组织分为表层区和心部区,表层区组织由细小α-Mg等轴晶和分布在晶界的Mg12Nd组成,心部区组织则由细小α-Mg等轴晶、粗大预结晶组织(ESCs)和分布在晶界的离异共晶Mg12Nd组成。在固溶处理过程中心部区晶粒的长大比表层区更为显著,晶界迁移速率与晶粒尺寸不均匀呈正相关性,满足晶粒长大模型v=M0exp (-Q/RT) A (1/D1-1/D2)。合金的优化热处理工艺为540℃×6 h+200℃×8 h。与铸态合金(UTS=186.0±1.5 MPa,YS=131±2.5 MPa,EL=6.6±0.4%)相比,峰值时效态合金的抗拉强度和屈服强度分别提高到了223.6±4.1 MPa和172.8±2.9 MPa,但延伸率降低到了4.2±0.3%。其强度的提高主要得益于时效析出的片状纳米β"相能够有效地阻碍位错在基面上的滑移。铸态和热处理态合金的表层区断裂模式均为韧性断裂,而心部区的断裂模式在铸态下为准解理断裂、在固溶态下为解理断裂、在峰值时效态下为准解理断裂。