Papers by Keyword: Constituents

Abstract: Abtrast: This research aimed to explore the antioxidant activity of microalgae oil through in vitro experiment and investigate the constituents of microalgae oil. The antioxidant activity was determined using the 1,1-diphenyl-2-picrylhydrazyl(DPPH)radical scavenging assay,2,2-Azinobis (3-ehtylbenzothiazolin-6-sulfnicAcid)(ABTS)radical scavenging assay, the reducing power,β-Carotene bleaching assay and Oxygen Radical Absorption Capacity(ORAC)assay. BHT、α-tocopherol or Vc were compared as the reference. It can be confirmed that microalgae oil has moderate antioxidant ability. According to GC-MS analysis, the most abundant compounds in microalgae oil were palmitic acid, docosahexaenoic acid and tetradecanoic,constituting 38.1%, 34.24% and 3.39%, respectively.

Abstract: The development of both dispersoid and constituent particle types during high temperature deformation has been investigated. Using torsion testing, which enables good temperature and strain rate control, the development of particles in terms of individual properties and the overall population has been examined during extended high strain rate deformation. Torsion tests also allow material that has the same thermal history but different levels of strain within a single sample to be compared. Quantitative comparison of particles has been performed using high resolution SEM imaging. Strain has been shown to have an important influence on particle evolution, beyond changing the kinetics of particle evolution alone. It has been demonstrated that the shape of the dispersoids is altered when they are evolving under the action of strain compared to that obtained from a thermal effect.

Abstract: The thermal stability of constituent particles in both as-cast and homogenised alloy AA7150 has been investigated by means of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results indicate that the as-cast eutectic starts to melt at 474°C and that the melting onset temperatures of the η- and S-phase particles after homogenisation are 474°C and 484°C, respectively. Two types of homogenisation treatments were used to dissolve eutectic particles: a two-step homogenisation treatment (40 h at 465°C + 4 h at 480°C) can completely dissolve the η- and S-based constituents, whereas a significant amount of S-phase still exists after a single-step homogenisation treatment of 40 h at 465°C. After utilising the two-step homogenisation treatment to dissolve all the η- and S-based constituents without overheating, samples were cooled at different controlled cooling rates and analysed by SEM and DSC to understand the effect of cooling rate on the type, size, distribution and density of precipitates formed during the cooling process. Slow cooling was found to result in the precipitation of coarse η-phase particles, with both the amounts and sizes of these η-phase particles increasing with decreasing cooling rate.

Abstract: The mineral constituents of a typical clay from Campos dos Goytacazes, Brazil, were investigated in terms of their nature and morphology by analytical methods including transmission electron microscopy and energy dispersive spectroscopy. The clay was found to have a large amount of finer, < 2 μm, aluminumsilicate particles of kaolinite and, in smaller proportion, halloysite, which is also an aluminumsilicate. At 1050oC the clay shows a consolidated structure with continuous glassy matrix in which Ti, Fe and Si oxides as well as mullite crystals are thoroughly embedded.

Abstract: The kinds, morphologies and distributions, enclosed the micro-structural evolvement of Al-1.5Si-1.1Mg-0.5Cu alloy during homogenization treatment were investigated by means of optical microscopy, XRD, SEM/EDS and TEM/EDS. The results show that there were mainly three kinds of morphologically distinct constituents in as-cast Al-1.5Si-1.1Mg-0.5Cu alloy for automotive panels, such as coarse Mg2Si and Al8(FeMn)2Si, and multiphase eutectic structure consisted of AlMgSiFeCu elements, except the α-Al matrix phase. The coarse Mg2Si and Al8(FeMn)2Si were distributed in the α-Al interdentritic regions or at grain boundaries, the former sometimes appears more obvious eutectic characteristics than the later one. The multiphase eutectic products distributed both inside grains with agglomerate aspects and along the α-Al interdentritic regions or at grain boundaries, which is contained with Si and Al2Cu. Coarse binary eutectic structure Mg2Si partly dissolved into matrix and the eutectic characteristics disappeared, whereas Al8(FeMn)2Si changed a little during homogenization. Agglomerate multi-eutectic structures were non-equilibrium products, some of them fully dissolved into matrix and the others partially dissolved and left the discrete blocky Si behind after homogenization.

Abstract: New affordable 2024 series aerospace aluminum alloy has been developed. Fracture toughness has been demonstrated increase in inverse proportion to the root of the distance between constituents, Cu2FeAl7, formed during ingot solidification. Higher fracture toughness material is obtained by means of combination of reduction of Fe content and wider spacing between the constituents. The fractured surface of those materials has been confirmed to show larger dimples due to the wider constituents. An outcome is the fracture toughness increases 20% through broadening the space from 75 to 140μm. Fatigue crack growth (FCG) has been governed by the morphology of dispersoids such as Cu2MnAl20, Cr2Mg3Al18 and ZrAl3, formed in homogenization process during heat treatment of ingot. In a low ΔK region, the FCG rate is slower when Cu2MnAl20 becomes larger. It is reconfirmed that the FCG rate is still faster for small dispersoids, Cr2Mg3Al18 or ZrAl3 bearing materials than Cu2MnAl20 bearing one through bridging effect of dispersoids. In a high ΔK region, on the other hands, the FCG rate becomes slower by broadening the spacing of the constituents. A new 2024 series alloy (2x24) with high fracture toughness and excellent FCG resistance has been developed on the basis of process- microstructure-structure methods.

Abstract: The complete evolution of solute content and second phases during full-scale industrial processing of AA3103 sheets has been measured. During pre-heating, dispersoids, which appear as plates or small polyhedra grow and the Mn solute content decreases. During subsequent breakdown rolling the dispersoid number-density increases significantly. The measured decrease of solute Mn after hot rolling and coil cooling is attributed to constituent particle growth, whereas the solute depletion during the final back-annealing is mainly caused by the growth of the dispersoids. These observations are compared to the predictions obtained by a semi-physical model for precipitation. Although simulations have been performed without any retro-fitting, for hot rolling the results compare quantitatively well with experiment, while for coil cooling and back annealing the modelled Mn solute depletion is underestimated. The precipitation process is found to be very sensitive to the microstructure, which illustrates the importance of coupling precipitation models with work hardening and softening models to obtain reliable predictions.

Abstract: This paper contains a review of microstructural through-process modelling (TPM) and the particular role of ingot metallurgy from an industrial perspective, focusing on recent advances in solidification theory, solidification and homogenisation software, and software environments that allow models to interface. To illustrate how as-cast microstructure can impact on downstream processing steps, a sensitivity analysis has been performed on an AA1xxx alloy using an in-house homogenisation model. Thus, knowledge gaps in theory and model application are highlighted.