Differential scanning calorimetry (DSC) and thermodynamic prediction of liquid fraction vs temperature for two high-performance alloys for semi-solid processing (Al-Si-Cu-Mg (319s) and Al-Cu-Ag (201))

There is a need to extend the application of semi-solid processing (SSP) to higher performance alloys such as 319s (Al-Si-Cu-Mg) and 201 (Al-Cu-Ag). The melting of these two alloys was investigated using differential scanning calorimetry (DSC) and thermodynamic prediction. The alloys had been processed by magneto-hydrodynamic (MHD) stirring before receipt to produce a microstructure suitable for SSP. The DSC results for the as-received MHD material were compared with those for material which has been taken through a complete DSC cycle and then reheated for a second DSC run. The effects of microsegregation were then analyzed. A higher liquid fraction for a particular temperature is found in the second DSC run than the first. Microstructural observations suggest this is because the intermetallics which form during the first cooling cycle tend to co-located. Quaternary and ternary reactions then occur during the second DSC heat and the co-location leads to enhanced peaks. The calculated liquid fraction is lower with 10 K/min DSC heating rate comparing with 3 K/min at a given temperature. The DSC scan rate must therefore be carefully considered if it is to be used to identify temperature parameters or the suitability of alloys for SSP. In addition, the starting material for DSC must represent the starting material for the SSP. With thermodynamic prediction, the equilibrium condition will provide better guidance for the thixoforming of MHD stirred starting material than the Scheil condition. The Scheil mode approximates more closely with a strongly microsegregated state

Influence of intensive melt shearing on the microstructure and mechanical properties of an Al-Mg alloy with high added impurity content

The official published version can be accessed from the link below - Copyright @ The Minerals, Metals & Materials Society and ASM International 2011We have investigated the influence of melt conditioning by intensive shearing on the mechanical behavior and microstructure of Al-Mg-Mn-Fe-Cu-Si alloy sheet produced from a small book mold ingot with high added impurity content. The melt conditioned ingot has fine grains throughout its cross section, whereas a conventionally cast ingot, without melt shearing, has coarser grains and shows a wider variation of grain size. Both needle-shaped and coarse Chinese script iron bearing intermetallic particles are found in the microstructure at the center of the conventionally processed ingot, but for the melt conditioned ingot, only fine Chinese script intermetallic particles are observed. In addition to the iron bearing intermetallics, Mg2Si particles are also observed. The ingots were rolled to thin sheet and solution heat treated (SHT). During rolling, the iron-based intermetallics and Mg2Si particles are broken and aligned along the rolling direction. Yield strength (YS), ultimate tensile strength (UTS), and elongation of the intensively melt sheared and processed sheet are all improved compared to the conventionally cast and processed sheet. Fractographic analysis of the tensile fracture surfaces shows that the clustered and coarse iron bearing intermetallic particles are responsible for the observed reduction in mechanical properties of the conventionally cast sheet. We have shown that by refining the initial microstructure of the ingot by intensive shear melt conditioning, it is possible to achieve improved mechanical properties at the final sheet gage of an AlMgMn alloy with a high content of impurities.This study is under the Technology Strategy Board funded REALCAR projec

Effects of Rapid Heating on Solutionizing Characteristics of Al-Si-Mg Alloys Using a Fluidized Bed

Effects of rapid heat transfer using a fluidized bed on the heat-treating response of Al-Si-Mg alloys (both unmodified and Sr modified) were investigated. The heating rate in the fluidized bed is greater than in conventional air convective furnaces. Particle size analyses of eutectic Si showed that the high heating rate during fluidized bed solution heat treatment causes faster fragmentation and spherodization of Si particles compared to conventional air convective furnaces. The mechanism of Si fragmentation through fluidized bed processing is through both brittle fracture and neck formation and its propagation. In contrast to this, the mechanism of Si fragmentation using a conventional air convective furnace is through neck formation and propagation. The Sr-modified D357 alloy showed a faster spherodizing rate than the unmodified alloy. Thermal analyses showed an exothermic reaction during solution heat treatment using a fluidized bed due to recrystallization, and coarsening of eutectic Al grains. Whereas the alloy solutionized using a conventional air convective furnace showed two exothermic reactions, one due to annihilation of point defects and the other due to recrystallization, and coarsening of the eutectic grains in the aluminum matrix. The recrystallization temperature of the alloy solutionized in the fluidized bed is lower than those in the conventional air convective furnace. Both tensile strength and elongation of fluidized bed solutionized alloys are greater than those solutionized using the air convective furnace. The optimum heat-treatment time for T4 temper using a fluidized bed for unmodified and Sr-modified alloy was reduced to 60 and 30 minutes, respectively

Favorable resuscitation characteristics in patients undergoing extracorporeal cardiopulmonary resuscitation:A secondary analysis of the INCEPTION-trial

Introduction: Extracorporeal cardiopulmonary resuscitation (ECPR) is increasingly used as a supportive treatment for refractory out-of-hospital cardiac arrest (OHCA). Still, there is a paucity of data evaluating favorable and unfavorable prognostic characteristics in patients considered for ECPR. Methods: We performed a previously unplanned post-hoc analysis of the multicenter randomized controlled INCEPTION-trial. The study group consisted of patients receiving ECPR, irrespective of initial group randomization. The patients were divided into favorable survivors (cerebral performance category [CPC] 1–2) and unfavorable or non-survivors (CPC 3–5).Results: In the initial INCEPTION-trial, 134 patients were randomized. ECPR treatment was started in 46 (66%) of 70 patients in the ECPR treatment arm and 3 (4%) of 74 patients in the conventional treatment arm. No statistically significant differences in baseline characteristics, medical history, or causes of arrest were observed between survivors (n = 5) and non-survivors (n = 44). More patients in the surviving group had a shockable rhythm at the time of cannulation (60% vs. 14%, p = 0.037), underwent more defibrillation attempts (13 vs. 6, p = 0.002), and received higher dosages of amiodarone (450 mg vs 375 mg, p = 0.047) despite similar durations of resuscitation maneuvers. Furthermore, non-survivors more frequently had post-ECPR implantation adverse events. Conclusion: The persistence of ventricular arrhythmia is a favorable prognostic factor in patients with refractory OHCA undergoing an ECPR-based treatment. Future studies are warranted to confirm this finding and to establish additional prognostic factors. Clinical trial Registration: clinicaltrials.gov</p

Favorable resuscitation characteristics in patients undergoing extracorporeal cardiopulmonary resuscitation:A secondary analysis of the INCEPTION-trial

Introduction: Extracorporeal cardiopulmonary resuscitation (ECPR) is increasingly used as a supportive treatment for refractory out-of-hospital cardiac arrest (OHCA). Still, there is a paucity of data evaluating favorable and unfavorable prognostic characteristics in patients considered for ECPR. Methods: We performed a previously unplanned post-hoc analysis of the multicenter randomized controlled INCEPTION-trial. The study group consisted of patients receiving ECPR, irrespective of initial group randomization. The patients were divided into favorable survivors (cerebral performance category [CPC] 1–2) and unfavorable or non-survivors (CPC 3–5).Results: In the initial INCEPTION-trial, 134 patients were randomized. ECPR treatment was started in 46 (66%) of 70 patients in the ECPR treatment arm and 3 (4%) of 74 patients in the conventional treatment arm. No statistically significant differences in baseline characteristics, medical history, or causes of arrest were observed between survivors (n = 5) and non-survivors (n = 44). More patients in the surviving group had a shockable rhythm at the time of cannulation (60% vs. 14%, p = 0.037), underwent more defibrillation attempts (13 vs. 6, p = 0.002), and received higher dosages of amiodarone (450 mg vs 375 mg, p = 0.047) despite similar durations of resuscitation maneuvers. Furthermore, non-survivors more frequently had post-ECPR implantation adverse events. Conclusion: The persistence of ventricular arrhythmia is a favorable prognostic factor in patients with refractory OHCA undergoing an ECPR-based treatment. Future studies are warranted to confirm this finding and to establish additional prognostic factors. Clinical trial Registration: clinicaltrials.gov</p

É atrativo tornar-se professor do Ensino Médio no Brasil?: Evidências com base em decomposições paramétricas e não paramétricas

Neste artigo avalia-se a atratividade da ocupação de professor do Ensino Médio, tal como expressa por diferenciais salariais entre essa categoria de professores e três grupos de comparação. Os dados provêm da PNAD, anos de 2006 e 2009, e as metodologias empregadas são a tradicional decomposição de Oaxaca-Blinder e uma alternativa não paramétrica proposta por Ñopo (2008), que decompõe em quatro termos o diferencial total, destacando o diferencial dentro de um suporte comum de características observáveis. Os resultados indicam que professores do Ensino Médio possuem diferencial de remuneração favorável, porém decrescente, quando comparados a funcionários públicos e empregados do setor privado. Além disso, e de modo mais preocupante, em comparação a profissionais com qualificação semelhante, a situação é desfavorável aos professores, e mostra deterioração de 2006 para 2009. Resultados obtidos utilizando ambas as metodologias indicam que este último diferencial em grande medida não é atribuível às diferenças nas distribuições de características individuais, mas muito mais à parcela não explicada, o que pode representar baixa valorização social de professores ou diferenciais de produtividade pré-escolha ocupacional ou pós-escolha ocupacional. Qualquer que seja a razão, o déficit de remuneração no mercado de trabalho docente pode ser um dos fatores explicativos do baixo interesse de jovens talentosos pelas licenciaturas com potenciais impactos negativos sobre a qualidade do aprendizado dos futuros alunos

Impact Toughness Enhancement of Melt Treated Al-Si-Mg Cast Alloy

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