Mg含量对Al-Zn-Mg铝合金组织及性能的影响

通过改变镁的含量,设计了4种不同成分的Al-6.0Zn-xMg合金。采用光学显微镜(OM)、扫描电镜(SEM)、差式扫描量热分析仪(DSC)、硬度、导电率以及室温拉伸等分析测试方法,研究了Mg含量对Al-Zn-Mg合金铸态、均匀化态组织性能及T6态力学性能的影响。结果表明:4种铸态合金组织晶界附近存在大量共晶网状结构与链状第二相,主要为α(Al)+三元T(AlZnMg)相,合金中还存在少量的Al₃(Zr,Ti)相和富铁相,提高Mg含量会使合金组织中的非平衡共晶相增加。合金均匀化处理后空冷,基体内有大量细小弥散的针状η(MgZn₂)相析出,且随着Mg含量的提高,这种针状η(MgZn₂)相的析出数量也逐渐增多。随着Mg含量增加,硬度逐渐增加,导电率逐渐下降,且均匀化态合金的硬度及导电率比铸态的高。4种T6态合金中Al-6.0Zn-2Mg合金的综合力学性能最佳。     

Hydrogen storage characteristics of composite TiCr1.8 + X wt.% LaNi5 alloys

In this paper, phase constituent, hydrogen storage characteristics and electrochemical performances of composite TiCr_1.8 + X wt.% LaNi₅ alloys with different stoichiometry were investigated. X-ray diffraction (XRD) tests reveal that these alloys still remain Laves phase constituent despite the increase of LaNi₅ content in alloys. Electrochemistry performance is improved whereas the maximum hydrogen storage capacity of pressure composition temperatures (PCT) test slightly decreases at the same time. One kind of alloy with capacity up to 55 mAh/g has been developed.     

半哈斯勒型磁制冷合金的研究进展

半哈斯勒型合金是近些年来受到国内外广泛关注的室温磁制冷材料之一。由于其原料较为低廉,因此其工业应用前景非常看好。依据其化学成分可大致分为co基、Ni基和Fe基三大类。合金化是调整这些合金相变温度和磁性能的重要手段。通过元素替换、掺杂以及化学计量比的变化不仅可以使半哈斯勒合金的磁性转变温度降低至室温附近,并且可以使其和结构相变温度之间的偏差尽量减小,从而为产生一级磁相变和巨磁热效应创造条件。预计今后几年合金化仍将是半哈斯勒型磁制冷合金研究的重要和热门方向之一。此外,合金的脆性和相变滞后也是值得关注的重要问题。     

Effect of atomic order on the martensitic transformation of Ni–Fe–Ga alloys

The effect of atomic order on martensitic transformation (MT) temperatures has been studied by differential scanning calorimetry in three polycrystalline alloys with compositions Ni_53.5+x–Fe_19.5−x–Ga_27.0 (x = 0, 0.5 and 1.5). Samples water quenched from different temperatures (470–1070 K) exhibit higher MT temperatures than ones slow cooled from the same temperature. This effect has been ascribed to a decrease of the L2₁ degree of order of the austenitic phase, which promotes an increase in the MT temperatures in these Ni–Fe–Ga alloys. The differences in ordering with cooling rate have been qualitative confirmed by electron diffraction patterns.     

Design criteria for high-temperature steels strengthened with vanadium nitride

Fe-8-12Cr ferritomartensitic steels are widely used in the power generation, petrochemical and nuclear industries where they are subject to high operating temperatures and stresses. Resistance to creep deformation is therefore a critical materials property. One method of providing creep resistance is to precipitate a fine homogeneous distribution of vanadium nitride (VN) particles in the matrix. Maximizing this precipitation hardening effect requires a high nitrogen content, but this could cause gas bubble formation during conventional fabrication processes. It is therefore necessary to determine how much N can be added without encountering such problems. Phase stability calculations, using Thermo-Calc, were carried out to find high-N compositions to optimize the fraction of VN and the fabrication route for obtaining fine particles. Several experimental compositions, including nine high-nitrogen alloys, were fabricated as ingots; out of these, two exhibited porosity Thermo-Calc predicts that, in all of the high-nitrogen alloys, nitrogen gas is a stable phase around the solidus temperature. It is evident that porosity cannot simply be predicted from the presence of the gas phase on the equilibrium diagram. However, detailed analysis of the equilibrium phases predicted in these alloys, including their variation with composition, allowed a porosity criterion to be obtained. This criterion links porosity formation to the nature of the liquid-to-solid transformation. Further calculations were carried out to predict the dependence of gas phase evolution on both composition and pressure. Thermodynamic calculations are a valuable tool for the design of these industrially important alloys. Input from experimental data has enabled the refinement of the initial design criteria such that it should now be possible to propose compositions with high VN hardening but without the risk of porosity. This paper was presented at the International Symposium on User Aspects of Phase Diagrams, Materials Solutions Conference and Exposition. Columbus, Ohio, 18–20 October, 2004.     

Sn含量对Zr-Sn-Nb-Fe-Cr合金相变温度和沉淀析出相的影响

以Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr与Zr-0.8Sn-0.3Nb-0.3Fe-0.1Cr2种不同Sn含量锆合金为研究对象,采用差示扫描量热法(DSC)测量2种锆合金的相变温度,探讨Sn含量变化对锆合金相变点的影响。同时,采用SEM对热轧态、热轧退火态、冷轧态、冷轧退火态、终轧态、终轧退火态6种加工工序样品分别进行详细的微观组织观察,随后通过定量金相法对2种锆合金在不同加工工序下的第二相大小及分布等特点进行对比分析,得出2种锆合金定量的统计结果。降低Sn含量对α→β相变点有明显影响,而沉淀析出相的颗粒形状基本不变,但是第二相颗粒平均尺寸减小。扫描电镜的能谱(EDS)分析半定量地说明Sn在锆合金中存在不同程度的成分偏析。     

Correlation Between Diagrams of Isothermal and Anisothermal Transformations and Phase Composition Diagram of Hardened Titanium Alloys

A brief review of works devoted to phase transformations in titanium alloys and published by the authors during a long period and of recent publications on the topic is presented. When plotting phase diagrams of hardened titanium alloys (metastable diagrams) the authors used as a basis their relationship to the equilibrium diagrams and the transformations of the -phase of various compositions during hardening from the -range temperatures. After studying the structure of hardened alloys they investigated their transformations during aging, isothermal treatment, and continuous cooling from the -range temperatures. Using the interrelation between the phase diagrams of hardened alloys and the phase transformations of -phase under various kinds of heat treatment the authors developed theoretical diagrams of isothermal and anisothermal transformations, which were later confirmed by experimental diagrams for pilot and commercial alloys. The suggested classifications of diagrams of isothermal and anisothermal transformations are applicable to titanium alloys of various structural classes with allowance for the coefficient K of stabilization of the -phase.     

Microstructure Characterization and Fracture Toughness of Laves Phase-Based Cr–Nb–Ti Alloys

Three Laves phase-based alloys with nominal compositions of Cr2Nb–x Ti(x = 20,30,40,in at%) have been prepared through vacuum non-consumable arc melting.The results show that the microstructures of Cr2Nb-(20,30) Ti alloys are composed of the primary Laves phase C15–Cr2(Nb,Ti) and bcc solid solution phase,while the microstructure of Cr2Nb–40Ti alloy is developed with the eutectic phases C15–Cr2(Nb,Ti)/bcc solid solution.The measured fracture toughness of ternary Laves phase C15–Cr2(Nb,Ti) is about 3.0 MPa m1/2,much larger than 1.4 MPa m1/2for binary Laves phase Cr2 Nb.Meanwhile,the fracture toughness of Cr2Nb–x Ti(x = 20,30,40) alloys increases with increasing Ti content and reaches 10.6 MPa m1/2in Cr2Nb–40Ti alloy.The eutectic microstructure and addition of Ti in Cr2 Nb are found to be effective in toughening Laves phase-based alloys.     

Experimental Investigation of Microstructure and Phase Transitions in Ag-Cu-Zn Brazing Alloys

Microstructure and phase transitions of selected brazing alloys from the Ag-Cu-Zn ternary system were investigated. Four ternary alloys with silver content in the compositional range from 25 to 60 wt.% were studied using x-ray diffraction (XRD) and scanning electron microscopy coupled with the energy-dispersive spectroscopy (SEM–EDS). Phase transitions of the investigated alloys were measured using differential scanning calorimetry (DSC). Experimentally obtained results were compared with the results of a thermodynamic calculation of the phase equilibria according to the CALPHAD method. The experiments confirmed the optimized thermodynamic parameters for the calculations from the thermodynamic assessment in literature. Phase compositions, liquidus and solidus temperatures were confirmed by the EDS and DTA methods. Additionally, the calculated solidification paths and predicted phase transformations were in agreement with the SEM images.     

Effects of V Addition on Microstructural Evolution and Mechanical Properties of AlCrFe2Ni2 High-Entropy Alloys

The effects of vanadium addition on the microstructural evolution and mechanical properties of AlCrFe₂Ni₂ high-entropy alloy (HEA) were investigated. The results showed that the AlCrFe₂Ni₂V_0.2 HEA was composed of FCC phase, disordered BCC phase, and ordered BCC (B2) phase. With the increase in vanadium content, the formation of FCC phase was inhibited, and a transition from FCC phase to BCC phase occurred. The FCC phase disappeared completely when the value of x exceeds 0.4 in AlCrFe₂Ni₂V_x HEAs. Besides, the amplitude-modulated microstructure morphology transformed from a B2 phase matrix with dispersed BCC nano-phase into an alternating interconnected B2 and BCC phases. Vanadium element has the function of stabilizing BCC phase and B2 phase in AlCrFe₂Ni₂V_x alloys. The hardness of AlCrFe₂Ni₂V_x alloys increased from HV 332.4 to HV 590.7, while the yield strength increased from 765 to 1744.6 MPa with increasing vanadium content, which was mainly due to the decreasing content of FCC phase and the solid solution strengthening of vanadium element. At the same time, the compression ratio of the alloys decreased with the disappearance of the FCC phase. Among the alloys, the AlCrFe₂Ni₂V_0.2 alloy possessed the most excellent comprehensive mechanical properties with yield strength, fracture strength, and compressive ratio 1231.1, 2861.9 MPa, and 44.5%, respectively.     

含二十面体准晶相Mg-Zn-Y合金的组织和性能

采用常规凝固技术制备了MgZn_6xY_x(x=0.7,1.0,1.5,2.0)合金,研究了Y含量对含有二十面体准晶相(I相)MgZn_6xY_x合金组织和性能的影响。结果表明,MgZn6xYx合金由α-Mg基体和分布在晶界周围的(α-Mg+I相)共晶组织组成。随着Y含量增加,基体晶粒尺寸减小,共晶组织尺寸增大,含量增加,由不连续分布转变为连续分布。在凝固过程中,二十面体准晶相通过共晶转变形成。Mg_89.5Zn_9.0Y_1.5合金的抗拉强度和伸长率达到最大值,分别为179.2MPa和3.5%。MgZn_6xY_x合金的断口呈现准解理断裂特征。     

Microstructure and mechanical behaviour of Nb–Al–V alloys with 10–25 at.% Al and 20–40 at.% V—I: microstructural observations

The microstructures of three Nb–Al–V alloys with nominal compositions Nb–10Al–20V, Nb–15Al–20V and Nb–25Al–40V (in at.%) have been investigated. It is shown that the alloys each exhibit an A2 or B2 matrix and often contain A15 and/or σ phase precipitates depending on thermal history. Both the A15 and σ phase precipitates exhibit two different well-defined orientation relationships and for the former these correspond to minimisation of elastic strain energy. ALCHEMI data from the B2 phase indicate that this is more stable for higher Al concentrations, and this is consistent with measurements of A2/B2 order-disorder transformation temperatures. In the alloy Nb–15Al–20V, the precipitation of the A15 phase in a supersaturated B2 matrix is preceded by the separation of the B2 phase into Al-rich domains in an Al-lean matrix.     

The influence of hot deformation on the microstructure of Ni-Al and Ni-Al-Fe alloys with small Ti2B addition

Results of microstructure investigation of Ni-Al and Ni-Al-Fe alloys with addition of 0.5at.% Ti₂B after hot deformation are presented. Ti partially dissolves in the matrix, promoting formation of a discontinuous phase and precipitates of γ′ phase of Ll₂ structure during hot deformation of Ni-Al and Ni-Al-4.3at.%Fe alloys. In all investigated alloys precipitates of different compositions, enriched in Ti, were noticed. A compression test proved that due to the grain boundaries strengthening, the fracture mechanism changes into a transcrystalline one, improving fracture toughness of the hot deformed alloy. Fracture occurs in the deformation induced Ll₀ martensite.     

铝含量和退火温度对锆铝合金相组成和力学性能的影响

利用非自耗电弧炉熔炼了Al含量为6.0%,7.0%,8.0%(质量分数)的锆铝二元合金,通过退火过程中的包析反应得到了不同相组成的Zr3Al基合金,借助光学显微镜、XRD分析研究了合金的金相组织和相组成,进行了显微硬度测定和拉伸试验。结果表明:铸态的锆铝合金显微硬度随着铝含量的增加而增大;退火可得到组织均匀的Zr3Al基合金,其显微硬度和抗拉强度主要与相组成和基体晶粒大小有关,而与第二相的形态无关;合金的显微硬度、抗拉强度随着Zr3Al相的增多而增大,延伸率随着Zr3Al相的增多而减小;合金的显微硬度、抗拉强度和延伸率随着Zr3Al晶粒的细化而不同程度地增大。     

Impacts of Microalloying Elements on the Hardening β"-Phase in Automotive AlMgSi Alloys

Microalloying elements play a crucial role in mechanical properties and phase stability of metallic alloys. In this work, we employ first-principles calculations and atomic-scale high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to find promising microalloying elements that will improve the stability and properties of β"/Al interface and β" phase in Al-Mg-Si alloys. First, we define a substitution energy for evaluating the stability of β" phase and β"/Al interface with microalloying elements doped. Then, experiments of HAADF-STEM imaging are carried out to verify the calculational results. Next, using the most stable structures doped with microalloying elements, the mechanical properties of the β" bulk and the β"/Al interface were calculated and analyzed. At last, we have figured out the effects of all considered microalloying elements and obtained a rule that the stable occupancy of solute atoms is related to their own radius and the radius of Mg, Si, and Al. These findings will provide some theoretical basis for future microalloying strategies of Al-Mg-Si alloys.     

Influence of Zn Content on Microstructures,Mechanical Properties and Stress Corrosion Behavior of AA5083 Aluminum Alloy

To enhance the stress corrosion cracking (SCC) resistance, Zn was utilized as an alloy element to add in the AA5083 aluminum alloys. The effects of Zn content on the microstructures, mechanical properties and SCC resistance were systematically evaluated. The results demonstrate that in the studied range adding Zn can significantly improve the SCC resistance of the AA5083 alloys. This is related to the relatively low amount of continuous β (Al₃Mg₂) phase along grain boundary and the formation of Zn-containing phase such as Al₅Mg₁₁Zn₄ phase. Based on the results, the optimal Zn content with respect to SCC resistance is approximately 0.50 wt.%. Further increasing Zn content results in coarse precipitates discontinuously distributed along grain boundaries.     

Phase identification and effect of W on the microstructure and micro-hardness of Ti2AlNb-based intermetallic alloys

The O-phase (orthorhombic Ti₂AlNb phase) intermetallic alloy has been considered one of the strongest materials for high temperature application. The primary compositions of the test alloys in this paper are Ti–22Al–27Nb (at.%) and Ti–22Al–20Nb–2W (at.%). By in-situ X-ray diffraction (XRD) tests, each phase is identified and the lattice parameters of each phase are calculated for different temperatures. XRD tests show that a Ti₂AlNb-β phase, partially ordered b.c.c. phase, exists besides O, ₂ and B2 that are usually expected in the Ti–Al–Nb alloy system. In this paper, the effects of tungsten on the microstructure and micro-hardness of a Ti₂AlNb-based (O+b.c.c.) alloy are investigated. The effects of W on Ti₂AlNb-based intermetallic alloys are widely known to cause a refinement of microstructure and improvement of mechanical strength, however, the reason has not yet been reported. In this paper, the role of W in the improvement of mechanical strength is clarified. The main effect of W addition is not the formation of a solid solution or the formation of W-precipitates but the refinement of the Widmanstätten structure.     

Hydrogen absorption characteristics of Pd1−xLix (x = 0.055 and 0.072) alloys and ordered Pd7Li

Thermodynamic quantities were determined for the absorption of hydrogen in Pd-5.5at.%Li and Pd-7.2at.%Li alloys, the latter alloy being in the two-phase field of saturated -Pd(Li,s) solid solution and the ordered Pd₇Li phase. Data were also determined for the Pd-10.6at.%Li alloy which consists only of the ordered Pd₇Li phase. The data were determined from measurements of pressure-composition isotherms at temperatures between 273 K and 463 K and hydrogen pressures up to 1000 Torr. The Pd---Li alloys dissolve considerable amounts of hydrogen and form a more stable hydride phase than Pd despite the lattice contraction which occurs on alloying Pd with Li. The hydrogen solubility in the ordered Pd₇Li phase alone is a little smaller than that in the two-phase mixture. The large hydrogen absorption of Pd---Li alloys, which does not depend on the presence of ordered Pd₇Li, may be attributed to (i) an attractive H---Li pair interaction, (ii) a decrease in the strain energies necessary for hydrogen occupation of the interstices, because of the similar lattice parameters of the -Pd(Li,s) and ordered Pd₇Li phases, and the large compressibility of Pd---Li alloys, and (iii) the valence of 1 of Li in Pd compared with 3 for, for example, Y in Pd.