铌在铀熔体中的溶解扩散行为研究

铀铌合金具有优异的抗腐蚀性能和良好的综合力学性能,是核工程中重要的结构与功能材料。通过直接真空感应熔炼的方式实现铀铌合金的合金化,可大幅度提高铀铌合金的生产效率。然而,铀铌合金的真空感应熔炼合金化过程易出现合金化不充分的现象,该问题主要与固态铌在铀熔体中的溶解扩散过程有关。为了提高对固态铌在铀熔体中的溶解扩散的认识,精确优化铀铌合金的真空感应熔炼工艺,提升铀铌合金材料质量,本文对固态铌在铀熔体中的溶解扩散行为进行了研究。通过溶解扩散实验获得铌在铀熔体中的溶解速率v与熔体温度T存在v=0.3651exp(-21150[K]/T)[m/s]关系;对U/Nb溶解扩散界面进行了表征,结果显示铌溶解于铀熔体的过程中,U/Nb溶解扩散界面形成了与固态Nb存在位向关系的片状结构;对比有无电磁搅拌情况下铌在铀熔体中的溶解行为及U/Nb界面结构,结果表明电磁搅拌提高了铌在铀中的溶解速率并改变了U/Nb界面的片状结构。     

Mg/Cu/Al接触反应钎焊工艺及元素扩散行为分析

采用铜中间层对镁合金与铝合金进行了接触反应钎焊,利用SEM,EDS研究了接头的微观形貌及组织结构,并对界面Cu元素的扩散行为进行了分析. 结果表明,铜中间层可有效阻隔镁与铝的接触反应,界面无Mg-Al系金属间化合物生成;相同温度下,Cu原子在Mg元素中的扩散能力远大于在铝中的扩散能力,导致Al/Cu侧在温度低于560 ℃时无法产生有效连接,且温度高于570 ℃时镁合金溶解过多,工艺区间过窄. 在565 ℃保温20 min可实现连接,但抗剪强度仅12.6 MPa. 采用低温长时间保温,随后高温短时加热的工艺可实现Mg/Cu/Al接头有效连接. 在475 ℃保温60 min,560 ℃加热7 min的条件下,接头强度可达31.2 MPa.     

Morphology and formation of Fe–Al intermetallic layers on iron hot-dipped in Al–Mg–Si alloy melt

We have examined the morphology and the growth of Fe–Al intermetallic layers of η-Fe₂Al₅ and θ-FeAl₃ phases formed on pure Fe sheets dipped in an Al-8.2Mg-4.8Si (wt.%) alloy melt and pure Al melt at 750 °C. The η phase layer grows one order of magnitude slower in the Al–Mg–Si alloy melt than in the pure Al melt. The change in thickness of Fe sheets with dipping time is less pronounced in the Al–Mg–Si alloy melt than in a pure Al melt. Microstructure observations suggest that the retarded interfacial reaction between solid Fe and liquid Al–Mg–Si alloy is associated with a continuous θ phase layer formed in the Al–Mg–Si alloy melt, which acts as the diffusion barrier.     

Stress-corrosion cracking of aged AlCuMg alloys in NaCl solution

Pitting potentials and stress corrosion life-times of AlCuMg alloys (mainly 2024 alloy) with various ageing structures have been measured in a de-aerated 1M NaCl solution under conditions of controlled potential. The aged alloy, which has the higher susceptibility to stress-corrosion cracking, showed two pitting potentials corresponding to pitting at the grain boundaries and within the grains. The susceptibility of the alloys to intergranular stress-corrosion cracking occurred at potentials above the pitting potential of the grain boundaries. The intergranular stress-corrosion cracking is caused not by the dissolution of the grain boundary precipitates (S phase) but by the pitting dissolution of the solute-denuded zones along the grain boundaries. Aspects of SCC in the alloys are similar to those in the Al-4%Cu alloy without Mg.     

Al-8.0Zn-2.0Mg-2.1Cu合金均匀化过程中Al2CuMg相的消除

采用光学显微镜(OM)、扫描电镜(SEM)、电子探针显微分析(EPMA)、X射线衍射(XRD)以及差示扫描量热仪(DSC)研究了一种高合金化Al-8.0Zn-2.0Mg-2.1Cu(wt%)合金在均匀化过程中难溶相Al₂CuMg的形成以及实现其充分溶解的工艺。结果表明:铸态时,合金中主要的非平衡凝固相为Mg(Zn, Al, Cu)₂相,Zn、Mg、Cu元素偏聚严重。经过470 ℃×40 h一级均匀化后,虽然Mg(Zn, Al, Cu)₂相逐渐回溶至基体中促进了合金中枝晶网络的基本消除,但合金中形成了一种耐高温的有害相Al₂CuMg。进一步采用485 ℃×14 h的高温均匀化工艺实现了合金中耐高温相Al₂CuMg的充分回溶。扩散动力学分析表明,470 ℃×40 h+485 ℃×14 h的双级均匀化工艺足以使合金中的非平衡相回溶至基体中。     

Synthesis of nanoporous copper by dealloying of Al-Cu-Mg amorphous alloys in acidic solution: The effect of nickel

Dealloying of Al-Cu-Mg based amorphous alloys in 1 M HCl solution and the effect of a minor amount of Ni in the precursor alloy were explored. A crystalline, Cu-rich, nanoporous structure with a pore diameter of 10–30 nm was formed as a result of the selective dissolution of Al and Mg and the reorganization of the remaining Cu. The entire specimen was fully dealloyed after prolonged exposure to a HCl solution. The nanoporous structure is finer (e.g. 10 nm) in the alloy containing Ni, likely because Ni suppresses the surface diffusion of Cu. The decrease in surface diffusion, in turn, suppresses the coarsening of the ligaments in the dealloyed layer enabling tunable porosity development. Electrochemical reactivity after the synthesis of nanoporous Cu was enhanced by a factor of 150 with Ni and 50 without Ni compared to a planar Cu electrode of the same overall dimensions.     

微量Ce对2090合金—纯Al扩散系统中Cu扩散系数的影响

测定了含Ｃｅ２０９０合金－纯Ａｌ扩散偶中Ｃｕ原子的浓度分布曲线，用Ｂｏｌｔｚｍａｎ－Ｍａｔａｎｏ法计算了扩散系数。结果表明：微量Ｃｅ可使Ｃｕ的扩散系数下降。Ｃｕ的扩散系数与其在扩散偶中浓度分布及浓度梯度有关。在合金中添加０．４０％Ｃｅ与添加０．２３％Ｃｅ相比，两者降低Ｃｕ扩散能力的效果相近。     

Enhanced Hydriding and Dehydriding Kinetics of as-Spun Nanocrystalline Mg2Ni-Type Alloy Substituting Ni with Cu

为了改善Mg2Ni型合金的吸放氢动力学性能,用Cu部分替代合金中的Ni。用快淬工艺制备了纳米晶Mg2Ni1-xCux(x=0,0.1,0.2,0.3,0.4)贮氢合金,用XRD、SEM、HRTEM分析了铸态及快淬态合金的微观结构;用自动控制的Sieverts设备测试了合金的吸放氢动力学性能。结果表明,快淬态合金具有纳米晶结构,Cu替代Ni不改变合金的主相Mg2Ni,但导致形成第二相Mg2Cu。随Cu含量的增加,合金的吸氢量先增加而后减小,但合金的放氢量随Cu含量的增加而单调增加。快淬显著提高合金的吸放氢量并改善合金的吸放氢动力学。     

Solidification behaviour of Al-7 %Si-Mg casting alloys

The effects of Mg content and cooling rate on the solidification behaviour of Al-7% Si-Mg(mass fraction)casting alloys have been investigated using differential scanning calorimetry, differential thermal analysis and microscopy. The Mg contents were selected as respectively 0.00%, 0.35% and 0. 70% (mass fraction). DTA curves of Al-7%Si-0.55%Mg(mass fraction) alloy at various cooling rates were accomplished and the alloy melt was cast in different cooling rates. The results indicate that increasing Mg content can lower the liquidus and binary Al-Si eutectic transformation temperatures. Large Fe-rich π-phases (AlsFeMg3Si6) are found in the 0.70% Mg alloys together with some small β-phases (Al5FeSi) ; in contrast, only β-phases are observed in the 0.35% Mg alloys. The test results of the Al-7%Si-0.55% Mg alloys identify that the liquidus and binary Al-Si eutectic transformation temperatures decrease, and the quantity of ternary Al-Si-Mg2 Si eutectic phase decreases as the cooling rate increases.     

铸造AlSi7Cu2Mg合金的变质处理研究

研究了不同的Sr含量对AlSi7Cu2Mg合金变质效果的影响。利用正交实验分析的方法,确定了主要影响因素。实验结果表明:Sr加入量、铝液温度和静置时间对于提高AlSi7Cu2Mg合金变质效果的影响程度大小的顺序是Sr加入量静置时间铝液温度,确定了AlSi7Cu2Mg合金的最佳的变质工艺,即Sr的加入量0.04wt%,静置时间60min,加入时铝液温度730℃。     

Effects of Cu addition on microstructure and mechanical properties of as-cast Mg-6Zn magnesium alloy

The application of Mg-Zn binary alloys is restricted due to their developed dendritic microstructure and poor mechanical properties. In this study, an alloying method was used to improve the mechanical properties of Mg-Zn alloy. The Mg-6Zn magnesium alloys microalloyed with varying Cu content(0, 0.8, 1.5, 2.0 and 2.5wt.%) were fabricated by permanent mould casting, and the effects of Cu content on the microstructure and mechanical properties of as-cast Mg-6Zn alloys were studied using OM, SEM, XRD and tensile tests at room temperature. The obtained results show that the addition of Cu not only can refine the grains effectively, but also can modify the eutectic morphology and improve the mechanical properties of the alloys. The main phases of the studied alloys include α-Mg, MgZn_2, Mg_2Cu and CuMgZn. When the content of Cu exceeds 0.8wt.%, Mg_2Cu phase appears. Meanwhile, the eutectic morphology is modified into dendritic shape or lamellar structure, which has an adverse effect on the tensile properties. Furthermore, among the investigated alloys, the alloy containing 0.8% Cu shows an optimalultimate tensile strength of 196 MPa, while the alloy with 1.5wt.% Cu obtains an excellent elongation of 7.22%. The experimental alloys under different Cu contents show distinguishing fracture behaviors: the fracture of the alloy with 0.8wt.% Cu reveals a mixed mode of inter-granular and quasi-cleavage, while in other investigated alloys, the fracture behaviors are dominated by cleavage fracture.     

The electrochemical behaviour of leaded brass in neutral CL and SO4 media

The electrochemical behaviour of lead brass with different leaded content in neutral chloride and sulphate solutions was investigated using the EIS technique. For comparison, the behaviour of the pure components of the alloy was investigated under the same conditions. The corrosion process was found to proceed via oxygen reduction following a diffusion controlled mechanism. The Cu electrode showed a higher polarization resistance due to film formation during oxygen reduction. Zn and Pb showed markedly lower impedance values due to continuous dissolution. The two investigated brass alloys (1.8% and 3.5% Pb, respectively) showed higher impedance values indicating the passivation of the surface in the Cl⁻ or SO₄⁻ media. Brass II was found to be more stable against corrosion indicating the beneficial effect of the lead content in the alloy.At cathodic potentials, the only process is the oxygen reduction. Anodic polarization leads to selective dissolution of Zn. At more positive potentials simultaneous dissolution of the alloy components with the deposition of Cu(I) salt takes place leading to the passivation of the alloy surface. At higher potentials, film breakdown occurs producing Cu(II) compounds whose diffusion control the corrosion process. At potentials higher than − 0.1 V, pitting corrosion was observed and a transmission line type in the impedance spectra was recorded.     

Transient liquid phase (TLP) brazing of Mg–AZ31 and Ti–6Al–4V using Ni and Cu sandwich foils

Transient liquid phase (TLP) brazing of Mg–AZ31 alloy and Ti–6Al–4V alloy was performed using double Ni and Cu sandwich foils. Two configurations were tested; first, Mg–AZ31/Cu–Ni/Ti–6Al–4V and second, Mg–AZ31/Ni–Cu/Ti–6Al–4V. The effect of set-up configuration of the foils on microstructural developments, mechanical properties and mechanism of joint formation was examined. The results showed that different reaction layers formed inside the joint region depending on the configuration chosen. The formation of ? phase (Mg), ρ (CuMg₂), δ (Mg₂Ni) and Mg₃AlNi₂ was observed in both configurations. Maximum shear strength obtained was 57 MPa for Mg–AZ31/Ni–Cu/Ti–6Al–4V configuration and in both configurations, the increase in bonding time resulted in a decrease in joint strength to 13 MPa. The mechanism of joint formation includes three stages; solid state diffusion, dissolution and widening of the joint, and isothermal solidification.     

Microstructural characteristics and paint-bake response of Al-Mg-Si-Cu alloy

The microstructural characteristics and paint-bake response of 6022 alloy with 0.3% Cu （mass fraction） were studied using optical microscope, scanning electron microscope（SEM）, transmission electron microscope（TEM） and tensile tester. The results indicate that the phase constituents in the as-cast microstructure are Mg2Si, Si, Al5Cu2Mg8Si6, Al5FeSi, α-Al（MnCrFe）Si and CuAl2. During the following homogenization, CuAl2, Al5Cu2Mg8Si6 and Mg2Si phases are almost completely dissolved, and Al5FeSi transforms to α-Al（MnCrFe）Si particles. After rolling, the phase constituents in the alloy change less except the precipitation of Mg2Si particles, and the precipitation behavior of Mg2Si strongly depends on the thermomechanical conditions. Cu addition significantly increases the paint-bake response of 6022 alloy by facilitating the formation of β＂ phase. Therefore, the tensile strength of 6022 alloy with 0.3% Cu is higher than that of 6022 alloy without Cu after paint-bake cycle.     

喷射沉积Al-Si-Ni-Cu-Mg合金的显微组织和相组成

利用喷射沉积技术制备了Ａ１Ｓｉ２０Ｎｉ４Ｃｕ３Ｍｇ合金,分析了合金沉积态、挤压态和Ｔ６热处理态的微观组织,结果表明,组织中存在三种含Ｎｉ的金属间化合物,在挤压和Ｔ６热处理时,它们能够有效地阻碍Ｓｉ原子的扩散,抑制初晶Ｓｉ的长大。此外,起常常强化作用的Ｃｕ与Ａｌ,Ｓｉ一起形成的金属间体例物,影响了合金在Ｔ６热处理时的沉淀强化作用。     

锌合金压铸射嘴身失效分析与提高其使用寿命的研究

根据射嘴身的工况,通过理论分析和损伤零件的破坏分析,确定了锌合金压铸射嘴身的失效机制,是锌合金熔体表面张力小、渗透性强、腐蚀性强、熔体腐蚀和应力腐蚀共同作用的结果。锌合金熔体能溶解钢材中的Fe、C、Si等元素,与Fe形成FeZn13相,同时C、Si、P、S等元素的存在,促进了Fe在锌合金熔体中的溶解,而形成锌合金压铸时特有射嘴身高温腐蚀问题。据此,提出了对射嘴身工作面进行稀土-B共渗,来阻止腐蚀发生和延长射嘴身的使用寿命;在稀土加入量为4%,加热温度为950℃,保温时间为7h,可获得60～70μm的渗B层。实际应用结果表明,经渗B的射嘴身使用寿命比未经处理的提高了4倍。     

Simulation study on function mechanism of some precipitates in localized corrosion of Al alloys

The function mechanism of different types of aging precipitates in localized corrosion of Al alloys was studied. The function mechanism of the precipitates of θ (Al₂Cu) and η (MgZn₂) is validated. The precipitate of θ containing noble element Cu is cathodic to the alloy base, resulting in the anodic dissolution and corrosion of the alloy base at its adjacent periphery. The precipitate of η containing active element Mg is anodic to the alloy base, anodic dissolution and corrosion occur on its surface. Meanwhile, a localized corrosion mechanism conversion associated with the precipitate of T1 (Al₂CuLi) is advanced, which contains noble element Cu and active element Li simultaneously. The precipitate of T1 is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Li and the enrichment of noble element Cu make its potential move to a positive direction. As a result, the corroded T1 precipitate becomes cathodic to the alloy base at a later stage, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery.     

Hydrogenation reaction of Mg-Based alloys fabricated by rapid solidification

Mg-23.5wt%Ni-xwt%Cu (x=2.5, 5 and 7.5) alloys for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The alloys were ground by a planetary ball mill for 2 h in order to obtain a fine powder. The Mg-23.5Ni-5Cu alloy had crystalline Mg and Mg₂Ni phases. Mg-23.5Ni-5Cu had an effective hydrogen capacity of near 5 wt%. The activated Mg-23.5Ni-5Cu alloy absorbed 4.50 and 4.84 wt%H at 573K under 12 bar H₂ for 10 and 60 min, respectively, and desorbed 3. 21 and 4.81 wt%H at 573K under 1.0 bar H₂ for 10 and 30 min, respectively. The activated Mg-23.5Ni-5Cu alloy showed a quite high hydriding rate like Mg-10Fe₂O₃, and higher dehydriding rates than the activated Mg-xFe₂O_3?yNi. This likely resulted because the melting before melt spinning process has led to the homogeneous distribution of Ni and Cu in the melted Mg, and the Mg-23.5Ni-5Cu alloy has a larger amount of the Mg₂Ni phase than the Mg-xFe₂O_3?yNi alloy.     

Interfacial phase formation of Al-Cu bimetal by solid-liquid casting method

The solid-liquid method was used to prepare the continuous casting of copper cladding aluminium by liquid aluminum alloy and solid copper, and the interfacial phase formation of Al-Cu bimetal at different pouring temperatures (700, 750, 800 ℃) was investigated by means of metallograph, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) methods. The results showed that the pouring temperature of aluminum melt had an important influence on the element diffusion of Cu from the solid Cu to Al alloy melt and the reactions between Al and Cu, as well as the morphology of the Al-Cu interface. When the pouring temperature was 800 oC, there were abundant Al-Cu intermetallic compounds (IMCs) near the interface. However, a lower pouring temperature (700 ℃) resulted in the formation of cavities which was detrimental to the bonding and mechanical properties. Under the conditions in this study, the good metallurgical bonding of Al-Cu was achieved at a pouring temperature of 750 ℃.     

球磨条件对Sn-0.7Cu合金形成的影响

通过对Sn、Cu混合粉末的机械球磨,利用X射线衍射仪、差热热分析仪和扫描电镜对粉末进行了检测与分析,研究了不同球磨条件对Sn-0．7Cu合金形成的影响。结果表明,电压、球料比及球磨时间对Sn-0．7Cu合金的形成有很大影响。对于Sn-Cu二元系,其机械合金化反应机制是通过机械诱发原子扩散,使原子间发生置换固溶和晶界溶解,而逐渐形成Cu4Sn5等合金相的。