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Influence of copper content on 6351 aluminum alloy machinability
Get PDFThe main purpose of this work is to study the influence of copper content on Al-Si-Mg aluminum alloy (6351) machinability. The machinability was evaluated through cutting tool torque and thrust force measurements, machined surface roughness, roundness, cilindricity and burrs formation, chip form and sub superficial modifications during drilling, reaming and tapping processes. The 6351 aluminum alloy samples were produced with five levels of copper (0.07%, 0.23%, 0.94%, 1.43% and 1.93%) with chemical composition of the other alloying elements practically constant within the recommended range by The Aluminum Association for this alloy. The main mechanical properties of the 6351 aluminum alloy samples were obtained by microstructural analysis and microhardness, hardness, tensile and impact tests. Major amounts of copper resulted in significant increase in microhardness, hardness and ultimate tensile strength of the aluminum alloy, while elongation after fracture decreased. A 23 factorial design was used to verify the effect of copper content and the cutting parameters, cutting speed and feed rate, in the machinability responses. Furthermore, an adjusted statistical model was developed to optimize the cutting parameters selection of the best copper content for each response. The results showed significant influence of copper content in machinability. Lower values of torque and thrust forces, lower roundness and cilindricity, better surface finish, besides smaller chips and burrs were obtained increasing copper content in Al-Si-Mg aluminum alloy (6351).CNPq - Conselho Nacional de Desenvolvimento Científico e TecnológicoTese (Doutorado)O objetivo principal deste trabalho é o estudo da influência do teor de cobre na usinabilidade da liga de alumínio 6351. A usinabilidade desta liga foi avaliada a partir dos resultados do torque e força na ferramenta de corte, rugosidade, desvios de forma (cilindricidade e circularidade) e rebarbas dos furos, forma dos cavacos e alterações subsuperficiais da peça durante os processos de furação, alargamento e rosqueamento. As amostras da liga de alumínio 6351 foram produzidas com diferentes teores de cobre (0,07%, 0,23%, 0,94%, 1,43% e 1,93%), e possuem composições químicas dos demais elementos de liga praticamente constantes dentro da faiXa recomendada pela Associação do Alumínio para esta liga. As principais propriedades mecânicas das amostras da liga de alumínio 6351 foram obtidas a partir de análises microestruturais e ensaios de microdureza, dureza, tração e impacto. O aumento da quantidade de cobre adicionada à liga de alumínio 6351 resultou em significativos aumentos de microdureza, dureza e limite de resistência à tração; e ao mesmo tempo na diminuição do alongamento percentual após a ruptura. A partir de um planejamento fatorial 23, foi verificado o efeito do teor de cobre e dos parâmetros de corte: velocidade de corte e avanço sobre as respostas de usinabilidade. Além disso, foi desenvolvido um modelo ajustado a fim de otimizar a seleção dos parâmetros de corte do melhor teor de cobre identificado para cada resposta. Os resultados mostraram influência significativa do teor de cobre sobre as repostas de usinabilidade medidas. Menores valores de torque e força de avanço, menores desvios de circularidade e cilindricidade, melhor acabamento superficial, além de menores cavacos e rebarbas foram obtidos a partir do aumento da quantidade de cobre presente na liga de alumínio 6351
Inhibition of localized attack on the aluminium alloy AA 6351 in glycol/water solutions
No full textA previous study had shown that exposure to degraded propylene glycol(PG)/water solution (1:1 in volume) at 80°C for 60 days or to boiling PG/water solution for 30 days induce remarkable localized attack on aluminium alloy AA 6351 (nominal composition: 1% Si, 0.6% Mg, 0.3% Mn, balance Al). In the present work degradation of the solution was achieved by holding the PG/water solution at its boiling temperature for 30 days in contact with AA 6351. The observed localized attack was mainly attributed to the action of copper ions dissolved from the aluminum alloy (copper content = 0.07%) and then deposited as small spots acting as efficient cathodic areas. The objective of this work was to examine the feasibility of enhancing pitting resistance of AA 6351 by adding suitable inhibitors to the solutions. The compounds used were two inorganic salts: sodium molybdate and sodium tungstate and two derivatives of pyrimidine: 2-aminopyrimidine (2AP) and 2-hydroxypyrimidine (2HP)
Influence of Copper Content on 6351 Aluminum Alloy Machinability
No full textAbstractThe main purpose of this work is to study the influence of copper content (Cu) in machining of 6351 aluminum alloy (Al-Si-Mg). The machinability was evaluated from measurements of drilling torque and drilling thrust force in cutting tool and surface roughness of the machined surface during drilling process. Samples of 6351 aluminum alloy were produced with different levels of copper (Cu) (0.07, 0.23, 0.94, 1.43 and 1.93%). Cutting speed and feed rate were varied in five levels (60 to 100 m/min and 0.1 to 0.3mm/rev). The results showed that increasing the copper content in a Al-Si-Mg-Cu aluminum alloy increase the precipitation hardening through the stabilization of hardening phases like Al5Cu2Mg8Si6 and Al2Cu, also the increase in amount of Al2Cu. Thus, the samples of 6351 aluminum alloy with higher copper content, in general, showed higher hardness and ultimate tensile strength values, while the percentage elongation after fracture was lower. The drilling torque and drilling thrust force during drilling process increased almost linearly with feed rate increase. The samples with higher amount of copper (1.43% and 1.93%) led to higher drilling torque and drilling thrust force for feed rate over than 0.2mm/rev. Although, the surface finishing of these samples machined holes was slightly worst
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
CORROSION IN SOLAR HEATING SYSTEMS. II. CORROSION BEHAVIOUR OF AA 6351 IN WATER/GLYCOL SOLUTIONS.
No full textA research was carried out in order to investigate the corrosion behaviour of the metals most commonly used as construction materials for solar absorber plates. With this in view, an attempt was made to test the corrosion resistance of AA 6351 aluminium alloy towards common uninhibited heat transfer fluids, such as ethylene and propylene glycol/water mixtures. Long time gravimetric tests consisted in up to 60 day exposures of the aluminium specimens to pure, chloride-polluted, or degraded glycol/water solutions, at 80 °C. The degradation into acidic products, experienced by heat transfer liquids in service, was simulated by keeping the ethylene and propylene glycol/ water solutions at their boiling temperatures for 30 days, in contact with copper.
In glycol/water solutions the presence of chlorides at low concentrations (200 ppm) caused the aluminium corrosion rates to increase by more than one order of magnitude, while in degraded solutions, containing 143 or 86 ppm cupric ions, corrosion rates higher than two order of magnitude with respect to pure solutions were obtained.
During the gravimetric tests, pitting corrosion was observed in some cases and its extent was rated by evaluating the deepest and the average metal penetration, the pit density and the average pit size.
The influence of heat transfer on AA 6351 alloy corrosion and on the couple Cu/AA 6351 efficiency was evaluated by gravimetric and electrochemical tests. Heat transfer through aluminium was found to significantly increase the AA 6351 pitting potential. On the contrary, it stimulated the aluminium galvanic corrosion, when applied on either aluminium or copper.
Under galvanic coupling conditions, the aluminium corrosion rates calculated from the average galvanic currents were a very little contribution to the gravimetric corrosion rates. This demonstrates that in low conductive solutions the risk of matching such dissimilar metals as copper and aluminium does not reside in the galvanic contact itself, but mainly in the presence of the noblest metal in the same solutions where aluminium is immersed
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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