Microstructural characterization of as-cast and homogenized 2D70 aluminum alloy

The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds (Al2CuMg, Al2Cu, Al9FeNi, Cu2FeAl7...     

Light metal compound casting

‘Compound casting’simplifies joining processes by directly casting a metallic melt onto a solid metal substrate. A continuously metallurgic transition is very important for industrial applications, such as joint structures of spaceframe constructions in transport industry. In this project, ‘compound casting’ of light metals is investigated, aiming at weight-saving. The substrate used is a wrought aluminium alloy of type AA5xxx, containing magnesium as main alloying element. The melts are aluminium alloys, containing various alloying elements (Cu, Si, Zn), and magnesium. By replacing the natural oxygen layer with a zinc layer, the inherent wetting difficulties were avoided, and compounds with flawless interfaces were successfully produced (no contraction defects, cracks or oxides). Electron microscopy and EDX investigations as well as optical micrographs of the interfacial areas revealed their continu- ously metallic constitution. Diffusion of alloying elements leads to heat-treatable microstructures in the vicinity of the joining interfaces in Al-Al couples. This permits significant variability of mechanical properties. Without significantly cutting down on wettability, the formation of low-melting intermetallic phases (Al3Mg2 and Al12Mg17 IMPs) at the interface of Al-Mg couples was avoided by applying a protective coating to the substrate.     

Effect of Ti–Si–Fe alloys on microstructure and properties of nitride/oxynitride bonded SiC ceramics sintered under CO/N2 atmosphere

Ti–Si–Fe alloys extracted from high-titanium blast furnace slag were utilized to replace part of the silicon powders, and then nitride/oxynitride bonded SiC ceramics were prepared by reactive sintering in graphite bed. Ti–Si–Fe alloys could react with CO/N₂ at a low temperature (1200 °C), and the addition of Ti–Si–Fe alloys could reduce the nitriding temperature of Si. Density functional theory calculations suggested that Ti–Si–Fe alloys enhanced reaction activity via weakening the strength of CO and NN bonds. The regional equilibrium phase diagrams of Si–C–N–O and Ti–Si–C–N–O under CO/N₂ atmosphere were calculated by thermodynamics. The change of whiskers morphology was observed by scanning electron microscope. Furthermore, the bulk density, the cold modulus of rupture, and the cold compressive strength improved with Ti–Si–Fe alloys content. The results showed that the addition of Ti–Si–Fe alloys not only significantly promoted nitriding of Si and formation of Si₃N₄ whiskers, but also improved the mechanical properties of the samples.     

红外吸收法测硅铁中的超低硫

应用高频红外碳硫仪,建立了硅铁合金中超低硫测定方法,对选择适当的测定条件如助熔剂、分析时间等进行了探讨,最佳测定条件:最大工作电流为400～480 mA;载气纯度为99.99%;陶瓷坩埚需经1 100℃灼烧2 h后,可使空白降至最小;硫元素最短分析时间为40 s,比较水平为5.00.     

Anomalous codeposition of Co–Ni: alloys from gluconate baths

Thin films of cobalt–nickel alloys were galvanostatically deposited onto steel substrates from gluconate baths. Cathodic polarization curves were determined for the parent metals and Co–Ni alloy. The effects of bath composition, current density and temperature on cathodic current efficiency (CCE) and alloy composition were studied. The deposition of Co–Ni alloy is of anomalous type, in which the less noble metal (Co) is preferentially deposited. The CCE of codeposition is high and increases with increase in temperature and current density, but it decreases as the [Co²⁺]/[Ni²⁺] ratio in the bath increases. The percentage of Co in the deposit increases with increasing cathodic current density, temperature and increasing Co²⁺ ion concentration. The structure and surface morphology of the deposit were studied by XRD, ALSV and SEM. The results showed that the alloys consisted of a single solid solution phase with a hexagonal close packed structure.     

Preparation of a self‐compatibility alloy via a seed‐graft concentrated‐emulsion pathway

A novel polymerization procedure, the concentrated‐emulsion graft polymerization of styrene monomer with poly(butyl acrylate) seed, was proposed for the production of a self‐compatibility macromolecule alloy. The effects of the butyl acrylate content, sodium dodecyl sulfate concentration, and polymerization temperature on the graft ratio were investigated. Scanning electron microscopy, transmission electron microscopy, and impact strength were used to characterize the microstructure and mechanical performance of the self‐compatibility macromolecule alloy. The results showed that increasing the butyl acrylate content, reducing the sodium dodecyl sulfate concentration, and improving the polymerization temperature all favored an increased graft ratio, which resulted in increased impact strength of the self‐compatibility macromolecule alloy. Therefore, the concentrated‐emulsion polymerization method is particularly suitable for seed‐graft polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2915–2920, 2002; DOI 10.1002/app.10288     

Oxidation and intergranular disintegration of the aluminides NiAl and NbAl3 and phases in the system Nb-Ni-Al

The oxidation behavior is very different for an aluminide with a wide homogeneity range such as -NiAl than for a line compound such as NbAl ₃.Oxidation of -NiAl at temperatures 1273 K leads to a slow-growing -alumina layer. The metal phase beneath the scale remains as -NiAl; however, cavity formation is observed. The cavity formation may be favored by sulphur surface segregation. Oxidation of NbAl ₃ at temperatures 1273 K initially leads to -Al ₂O₃,but the Al depletion causes the formation of Nb ₂ Al beneath the oxide layer. Cracking of the Al ₂O₃ layer opens Nb ₂ Al to the atmosphere, which oxidizes rapidly to Nb ₂O₅ and NbAlO₄.After consumption of the Nb ₂ Al, a layer of Al ₂O₃ formed again on the NbAl ₃ phase, but failure of the alumina and the fast growth of the other oxides occur as a repeated process. Thus, NbAl ₃ exhibited rapid linear oxidation kinetics. Multiphase alloys in the system Nb-Ni-Al generally behave better than NbAl ₃,and the low oxidation rates of -NiAl can be approached. In the temperature range below 1273 K, with a maximum at 1000 K, both NiAl and NbAl ₃ show the pest phenomenon, an intergranular disintegration. Preceding the disintegration, oxygen diffuses into the grain boundaries of the material and Al ₂O₃ is formed at the grain boundaries, beginning from the surface region. NiAl is susceptible only in a very limited range of oxygen pressures and temperatures, whereas NbAl ₃ is much more susceptible.     

Evolution of insoluble eutectic Si particles in anodic oxidation films during adipic-sulfuric acid anodizing processes of ZL114A aluminum alloys

The effects of insoluble eutectic Si particles on the growth of anodic oxide films on ZL114A aluminum alloy substrates were in-vestigated by optical microscopy (OM) and scanning electron microscopy (SE...     

Effect of rare earth samarium addition on the kinetics of precipitation in AI-Cu-Mn casting alloy

The mechanical properties of Al-Cu-Mn casting alloy mainly depend on the morphology, distribution, size, and number ofθ′（Al2Cu） precipitates. In this study, we have analyzed the effect of rare earth samarium （Sm） addition on the kinetics of precipitation in the Al-Cu-Mn casting alloy by using differential scanning calorimetry （DSC） and high-resolution transmission electron microscopy. Thermal ef-fect peaks that are attributed to the formation and the dissolution of Guinier-Preston （GP） zone andθ′phase were identified from the DSC curves. The activation energy ofθ′formation was calculated by using both the Kissinger method and the analytical model, and the corre-sponding results were compared. Results suggest that the activation energy ofθ′formation in Al-Cu-Mn alloy is dramatically higher than that in Al-Cu-Mn-Sm alloy. Accordingly, it is concluded that the addition of rare earth Sm decreases the activation energy ofθ′formation and promotes the formation ofθ′precipitates.