1,720,985 research outputs found
Microstructural and mechanical properties characterization of heat treated and overaged cast A354 alloy with various SDAS at room and elevated temperature
No full textThe aim of the present study was to carry out a microstructural and mechanical characterization of the A354 (Al-Si-Cu-Mg) cast aluminum alloy. The effect of microstructure on the tensile behaviour was evaluated by testing samples with different Secondary Dendrite Arm Spacing, (SDAS) values (20-25 μm and 50-70 μm for fine and coarse microstructure, respectively), which were produced through controlled casting conditions. The tensile behaviour of the alloy was evaluated both at room and elevated temperature (200 °C), in the heat treated and overaged (exposure at 210 °C for 41 h, after solution heat treatment) conditions. Optical, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) were used for microstructural investigations.
Experimental data confirmed the significant role of microstructural coarseness on the tensile behaviour of A354 alloy. Ultimate tensile strength and elongation to failure strongly increased with the decrease of SDAS. Moreover, solidification rate influenced other microstructural features, such as the eutectic silicon morphology as well as the size of the intermetallic phases, which in turn also influenced elongation to failure. Coarsening of the strengthening precipitates was induced by overaging, as observed by STEM analyses, thus leading to a strong reduction of the tensile strength of the alloy, regardless of SDAS. Tensile properties of the alloy sensibly decrease at elevated temperature (200 °C) in all the investigated heat treatment conditions
Effect of Mo Addition on Room and High Temperature Tensile Behavior of Al-Si-Cu-Mg Alloy in As-Cast and Heat-Treated Conditions
No full textThis study focuses on the role of Mo addition on the mechanical properties of an Al-Si-Cu-Mg alloy in as-cast and heat-treated condition at ambient and elevated temperature. Addition of 0.4 to 0.6 wt.% Mo forms Mo-bearing dispersoid particles which have a relatively high melting point and improve high temperature tensile strength. Ductility suffered in the presence of Mo-bearing particles. Trace addition of Mo up to 0.6 wt.% has a negligible influence on the yield strength and hardness of Al-Si-Cu-Mg alloy in as-cast and heat-treated conditions at ambient temperature and 250 °C
Mechanical Performance of Nodular Cast Irons After Prolonged High-Temperature Exposure
No full textDuctile cast irons (DIs) are widely used in industrial applications. Their use is, however, often limited to components working at room temperature, since prolonged exposure at high temperature can lead to decomposition of both ausferrite and pearlite, with a consequent strength reduction. The present paper evaluated the effects of prolonged high-temperature exposure on microstructure and residual strength of DIs with different matrices, after an isothermal soaking at temperatures between 200 and 600 °C. Microstructural analyses highlighted that long-term exposure at temperatures higher than 500 °C leads to the complete decomposition of ausferritic and pearlitic matrix microstructures, while hardness tests showed that the hardness is stable up to 500 °C for the pearlitic ductile iron (PDI), up to 450-500 °C for the ausferritic ductile iron (ADI) and up to 400-450 °C for the perferritic isothermed ductile iron (IDI). Exposure at 500 °C for 240 h induces a reduction in tensile strength of IDI and ADI, respectively, of 10 and 25% (for both room temperature and 500 °C tensile testing), while it has no significant effects on PDI
The influence of cooling rate on microstructure, tensile and fatigue behavior of heat-treated Al-Si-Cu-Mg alloys
No full textAl-Si-Mg alloys are commonly employed for the production of automotive castings. In view of the recent stringent emissions standards and consequent engine downsizing, these components must withstand higher temperatures and stresses than in the past. In this regard, the heat treatable quaternary Al-Si-Cu-Mg alloys gained particular interest in recent years, due to their superior mechanical properties and higher thermal stability. The present research activity was addressed to evaluate the influence of cooling rate on microstructure and consequently on room temperature tensile and fatigue behaviour of the A354 and C355 alloys. Samples for mechanical tests were produced under controlled cooling rates, in order to induce different secondary dendrite arm spacing (SDAS) values, classified as fine (20-25μm) and coarse (50-70μm). The experimental results showed that the cooling rate strongly influences the type, size and morphology of intermetallic particles. The presence of coarse intermetallic phases, mostly Fe-based, observed in coarse SDAS specimens, was reported to strongly affect ultimate tensile strength (UTS), elongation to failure and fatigue strength of both the investigated alloys. A correlation between UTS and fatigue resistance was found, independent of microstructural coarseness
Room and high temperature fatigue behaviour of the A354 and C355 (Al-Si-Cu-Mg) alloys: Role of microstructure and heat treatment
No full textAl-Si-Mg alloys are widely used in the automotive industry for the production of engine components. Due to the new stringent emissions standards, these components undergo higher temperatures than in the past; as a result, alloys with higher thermal stability, such as the Al-Si-Cu-Mg, are currently under investigation.
The present paper aims at widening the knowledge on the relationship between room temperature (RT) and high temperature fatigue behaviour of A354 and C355 alloys and their microstructural features, in particular, secondary dendrite arm spacing (SDAS) and intermetallic compounds. Samples for fatigue characterization were hot isostatic pressed, aiming to avoid the effect of solidification defects.
The results of microstructural analyses and bending fatigue tests highlighted that (i) SDAS influences room temperature fatigue behaviour of the peak-aged A354 and C355 alloys, while its effect on the overaged alloys at high temperature is negligible; (ii) fatigue cracks nucleated mostly from large intermetallic compounds; (iii) at room temperature, C355 alloy is characterized by higher fatigue strength (151 and 135 MPa for fine and coarse SDAS, respectively) in comparison to A354 alloy (133 and 113 MPa); after overaging and testing at high temperature, the behaviour of the two alloys is comparable. A good correlation between ultimate tensile strength and fatigue resistance was found, independent of microstructure and aging conditio
Influence of Sludge Particles on the Fatigue Behavior of Al-Si-Cu Secondary Aluminium Casting Alloys
Full text linkAl-Si-Cu alloys are the most widely used materials for high-pressure die casting processes. In such alloys, Fe content is generally high to avoid die soldering issues, but it is considered an impurity since it generates acicular intermetallics (β-Fe) which are detrimental to the mechanical behavior of the alloys. Mn and Cr may act as modifiers, leading to the formation of other Fe-bearing particles which are characterized by less harmful morphologies, and which tend to settle on the bottom of furnaces and crucibles (usually referred to as sludge). This work is aimed at evaluating the influence of sludge intermetallics on the fatigue behavior of A380 Al-Si-Cu alloy. Four alloys were produced by adding different Fe, Mn and Cr contents to A380 alloy; samples were remelted by directional solidification equipment to obtain a fixed secondary dendrite arm spacing (SDAS) value (~10 μm), then subjected to hot isostatic pressing (HIP). Rotating bending fatigue tests showed that, at room temperature, sludge particles play a detrimental role on fatigue behavior of T6 alloys, diminishing fatigue strength. At elevated temperatures (200 °C) and after overaging, the influence of sludge is less relevant, probably due to a softening of the α-Al matrix and a reduction of stress concentration related to Fe-bearing intermetallics
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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