1,721,021 research outputs found
Review of microstructures and properties of zinc alloys
Full text linkAccording to market data, about 15% of world zinc consumption is devoted to the production of zinc-base alloys that are used for manufacturing automotive parts, electronic/electrical systems and also, water taps and sanitary fittings, household articles, fashion goods, etc. These alloys are characterized by low melting points and high fluidity that make them suitable for foundry applications. Typically, they are processed by hot chamber high-pressure die-casting where can be cast to thicknesses as low as 0.13 mm. The die-cast zinc alloys possess an attractive combination of mechanical properties, permitting them to be applied in a wide variety of functional applications. However, depending on the alloying elements and purposes, some zinc alloys can be processed also by cold chamber die-casting, gravity, or sand casting as well as spin casting and slush casting. In this paper, a detailed overview of the current knowledge in the relationships between processing, microstructure and mechanical properties of zinc-base alloys will be described. In detail, the evolution of the microstructure, the dimensional stability and aging phenomena are described. Furthermore, a thorough discussion on mechanical properties, as such as hardness, tensile, creep, and wear properties of zinc-base alloys is presented
NO2 adsorption at ambient temperature on urea-modified ordered mesoporous carbon
No full textA soft-templated ordered mesoporous carbon was synthesized, impregnated with urea and pyrolyzed at 500 and 800 degrees C. The samples obtained were tested as NO2 adsorbents. Their structural properties and surface chemistry, before and after NO2 exposure, were investigated using nitrogen adsorption, TEM, potentiometric titration and thermal analysis. Results showed that the ordered mesoporous structure remains stable throughout the treatment applied and exposure to NO2. Even though the initial carbon exhibited a high NO2 adsorption capacity, the incorporation of nitrogen groups to the carbon surface, resulted in the further improvement of the performance after heat treatment. The mechanism of reactive adsorption was found to be significantly affected by surface chemistry of mesoporous carbons. (C) 2013 Elsevier Ltd. All rights reserved
Study of high temperature properties of AlSi10Mg alloy produced by laser-based powder bed fusion
No full textAdditive manufacturing of Al alloys can represent an interesting solution for highperformance components in various industrial fields, as for instance the automotive and aerospace industry. Often, for these applications, the alloys are required to withstand exposure to high temperatures. Therefore, the investigation of the evolution of material properties with increasing temperature is of utmost importance in order to assess their suitability for this kind of applications. In the present study, tensile properties at high temperature were investigated for an AlSi10Mg alloy. Samples were manufactured by laser-based powder bed fusion in horizontal and vertical direction in order to examine the influence of building direction on material behavior. The samples were tested in as-built condition and after exposure to high temperature. Tensile tests were performed up to 150 °C and the effect of holding time at the test temperature was evaluated. Furthermore, the alloy was characterized by mechanical spectroscopy in order to evaluate the behavior of dynamic modulus with temperature and, thus, to provide a comprehensive characterization of the material behavior. It was found that the peculiar microstructure of the alloy produced by additive manufacturing is responsible for good high-temperature strength of the material up to 150 °C. The material also exhibits a good thermal stability even after holding at test temperature for 10 h
Mechanical spectroscopy study of as-cast and additive manufactured AlSi10Mg
Full text linkThe AlSi10Mg alloy produced by casting (AC) and additive manufacturing (AM) technology of laser powder bed fusion (L-PBF) has been investigated through mechanical spectroscopy (MS). In addition to the grain boundary peak PGB the Q−1 curves of both materials exhibit two other relaxation peaks, P1 (H = 0.8 ± 0.05 eV; τ0 = 10−11±1 s) and P2 (H = 1.0 ± 0.05 eV; τ0 = 10−13±1 s), depending on the interaction of dislocations with solute elements (Si and Mg). Relaxation strengths of P1, P2 and PGB of AM alloy are greater than those of the AC one owing to the finer structure of Al cells and the higher amount of Si and Mg in supersaturated solid solution induced by the rapid solidification typical of the L-PBF process. After successive MS test runs relaxation strengths of P1 and P2 peaks in both the examined materials decrease due to the precipitation of Si atoms and dislocation density recovery. Such decrease is more pronounced in AM alloy where change of cell shape and increase of cell size is observed. Dynamic modulus of AM alloy exhibits an anomalous trend in the first test run that is no more present in successive runs. The irreversible process giving rise to such anomalous behavior is the closure of pores of nanometric size
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effect of a New High-Pressure Heat Treatment on Additively Manufactured AlSi10Mg Alloy
Full text linkThe application of an innovative high-pressure T6 treatment (HPT6) to additively manufactured AlSi10Mg alloy is reported in this paper. The aim of this treatment is to obtain the effective densification of the material together with the hardening effects typical of T6 heat treatment in one step. For comparison, a two-step treatment consisting of hot isostatic pressing followed by conventional T6 treatment was applied. Standard annealing and T6 treatment alone were also considered. The microstructural and mechanical properties of alloys treated under all the studied conditions were analyzed and their density was measured to quantify their densification. Although the application of high pressure hindered the diffusion mechanisms, and thus could limit the hardening effect of heat treatment, HPT6 treatment was found to ensure suitable mechanical properties and high densification. Furthermore, it required less time; therefore, it can be considered as a time-efficient process for high-performance applications
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Wear Behavior of AlSi10Mg Alloy Produced by Laser-Based Powder Bed Fusion and Gravity Casting
Full text linkHerein, the sliding wear behavior of AlSi10Mg samples realized using laser-based powder bed fusion (LPBF) is investigated via pin-on-disc (PoD) tests, before and after T6 heat treatment. The changes in the microstructure, density, and hardness induced by heat treatment are correlated with the tribological behavior of the alloy. Furthermore, short wear tests are conducted and the resulting wear tracks are investigated through scanning electron microscopy (SEM), equipped with an energy-dispersive spectroscopy (EDS) microprobe to elucidate how the wear mechanisms evolve with sliding distance. For comparison, gravity cast (GC) AlSi10Mg samples are also characterized and tested. The as-built additive manufacturing (AM) sample exhibits the lowest wear rate and coefficient of friction because of its high hardness and relative density, whereas the heat-treated sample shows the worst behavior in comparison with the GC samples. The results suggest a significant influence of porosity on the wear behavior of AM alloys
Characterization of microstructural and mechanical properties of high-pressure die-cast en ac 46000 alloy
No full textThe present research focuses on the characterization of microstructural and mechanical properties of real castings produced by HPDC using EN AC 46000 alloy. The Cu content of the alloy was varied inside the limits prescribed by the standard for EN AC 46000 alloy to investigate the influence of Cu on the material performance and to provide results useful for industrial applications. Castings with Cu content of 2 wt,% and 4 wt.% were industrially produced using a 2500-ton HPDC machine. Two areas of the casting with different cooling rates were selected to obtain samples for microstructural and mechanical characterization. In particular, area fraction, number density and equivalent diameter of intermetallic compounds were investigated, and the size distribution of these particles were statistically evaluated. Finally, hardness measurements and tensile tests were performed and the results were correlated to microstructural features and solidification conditions to deeply understand the alloy behavior
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