Fundamental study of hot tearing mechanisms of aluminium-silicon alloys

Hot tearing is a common defect during DC casting of some commercial aluminum alloys and can result in considerable productivity loss in the cast-house. In order to better understand the hot tearing, a novel technique, dubbed DCSS for Direct Chill Surface Simulator, has been developed to reproduce the cooling conditions at the mould/liquid metal interface and to generate the unique surface and sub-surface microstructure of the DC ingot. The apparatus has been designed also to apply and measure a tensile load and the surface strain. These mechanical quantities were then used to derive the stress-strain curves that best represent the material behaviour during solidification and its capacity to resist hot tearing.The present work describes the approach used to determine the mechanical resistance of three different aluminum-silicon binary alloys (AI-0.5wt%Si, Al-1.5wt%Si, and Al-2.5wt%Si). In addition, the present work covers the modeling of the heat transfer encountered during the test using commercial software (ProCAST(TM)) to better understand the temperature field upon solidification and tracking the solid fraction. Microstructure analyses were made to obtain various metallurgical quantities (e.g., grain morphology, size), physical measurements and thorough investigation of the torn surfaces. Information was used as inputs to the various models developed and used in the present work.A theoretical model was updated from previous work using more realistic metallurgical quantities. This research led also to the development of a probalistic model (cellular automata) to simulate the microstructure of the cast sample. The model has been used to determine a crack propagation coefficient (CPC) that was used in the theoretical model to better represent the hot tear propagation.Work to include even more complex coupled phenomena such as creep phenomena and microsegregation are not covered in the present scope of this work. Hypotheses are raised according to experimental work and observations made that suggest their most probable contributions. These studies have advanced to a certain degree the scientific understanding of hot tearing such as the inherent mechanical behaviour during solidification. In addition, the DCSS was used successfully to rank DC cast commercial wrought alloys in terms of hot tearing susceptibility

Evaluation of plasma 3-methoxy-4-hydroxyphenylglycol

A high-performance liquid chromatographic (HPLC) assay suitable for the evaluation of 3-methoxy-4-hydroxyphenylglycol (MHPG) in 1-ml aliquots of plasma is presented. Preparatory steps include extraction into ethyl acetate and minicolumn chromatography. Recoveries are monitored with [3H]MHPG. The HPLC procedure utilizes a C18 column, isocratic elution and amperometric detection. The assay was checked against a gas chromatographic--mass spectrometric procedure; the two procedures correlated well with a correlation coefficient of 0.99. Intra-assay reproducibility was 5.4%, inter-assay reproducibility 10.7%. Immediate changes in the orthostatic position did not affect the plasma MHPG concentration. Based on 22 normal controls the daytime plasma MHPG level was 2.98 +/- 0.66 ng/ml (mean +/- S.D.).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26347/1/0000434.pd

Exome-wide association study to identify rare variants influencing COVID-19 outcomes : Results from the Host Genetics Initiative

Publisher Copyright: Copyright: © 2022 Butler-Laporte et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Host genetics is a key determinant of COVID-19 outcomes. Previously, the COVID-19 Host Genetics Initiative genome-wide association study used common variants to identify multiple loci associated with COVID-19 outcomes. However, variants with the largest impact on COVID-19 outcomes are expected to be rare in the population. Hence, studying rare variants may provide additional insights into disease susceptibility and pathogenesis, thereby informing therapeutics development. Here, we combined whole-exome and whole-genome sequencing from 21 cohorts across 12 countries and performed rare variant exome-wide burden analyses for COVID-19 outcomes. In an analysis of 5,085 severe disease cases and 571,737 controls, we observed that carrying a rare deleterious variant in the SARS-CoV-2 sensor toll-like receptor TLR7 (on chromosome X) was associated with a 5.3-fold increase in severe disease (95% CI: 2.75–10.05, p = 5.41x10-7). This association was consistent across sexes. These results further support TLR7 as a genetic determinant of severe disease and suggest that larger studies on rare variants influencing COVID-19 outcomes could provide additional insights.Peer reviewe

Development of a versatile rheocasting technology

Since 2003, a concerted effort between Alcan Inc. (ARDC: Arvida Research and Development Centre) and the Aluminium Technology Centre (ATC) of the National Research Council of Canada is underway to develop a technology, dubbed SEED (Swirled Enthalpy Equilibration Device), to produce semi-solid aluminium feedstock. This technology, patented by Alcan Inc., is a simple process offering many advantages over thixocasting, especially for reducing the cost of feedstock. The process involves two main steps: 1) heat extraction to achieve a desired liquid/solid mixture, and 2) drainage of an excess liquid to produce a self-supporting semi-solid slug that is cast in a high pressure press. This paper reports that the SEED technology is applicable to a number of aluminium alloys and can be easily adapted to produce a wide range of slug dimensions. Furthermore, since the heat transfer plays a predominant role during the manufacture of the semi-solid slurry, its analysis is also presented.Peer reviewed: YesNRC publication: Ye

Effect of Si, Cu and Fe on mechanical properties of cast semi-solid 206 alloy

The development of a modified 206 alloy whose composition was optimized to minimize hot tearing during semi-solid forming was reported. The effect of varying silicon, copper and iron contents was investigated using a design of experiment (DOE) approach. Semi-solid slurries were prepared using the SEED process and injected into a high pressure die casting press. The hot tearing sensitivity results were reported for different alloy variants. The microstructure evolution during the semi-solid preparation was presented along with actual die cast components. The effects of silicon, copper and iron on mechanical properties in the T7 condition were also analyzed. Beyond the benefit of reducing hot tearing, it is shown that the tensile and fatigue properties remain compatible with the automotive industry requirements.Le pr\ue9sent article rapporte la mise au point d\u2019une modification de l\u2019alliage 206 en optimisant sa composition pour limiter les criques de solidification au cours du moulage semi-solide. L'utilisation d'une approche de plan d\u2019exp\ue9rience a permis d'\ue9tudier l\u2019effet des variations de contenu en silicium, en cuivre et en fer. Des lopins semi-solides ont \ue9t\ue9 pr\ue9par\ue9s en utilisant le proc\ue9d\ue9 SEED et inject\ue9s dans une presse de moulage sous pression. Les r\ue9sultats de sensibilit\ue9 aux criques de solidification ont \ue9t\ue9 obtenus pour diff\ue9rentes variantes de l\u2019alliage. On a examin\ue9 l\u2019\ue9volution des microstructures au cours de la pr\ue9paration de la p\ue2te semi-solide de m\ueame que les composantes moul\ue9es sous pression obtenues. Les effets du silicium, du cuivre et du fer sur les propri\ue9t\ue9s m\ue9caniques en condition T7 ont \ue9galement \ue9t\ue9 analys\ue9s. Au-del\ue0 d\u2019une r\ue9duction des criques de solidification, ces travaux montrent \ue9galement que les propri\ue9t\ue9s de r\ue9sistance et de fatigue demeurent compatibles avec les exigences de l\u2019industrie automobile.Peer reviewed: YesNRC publication: Ye

Proc\ue9d\ue9 SEED et moulage sous pression de pi\ue8ces d\u2019aluminium : Description du proc\ue9d\ue9 et transfert de chaleur

Depuis le d\ue9but 2003, le CRDA (Centre de recherche et d\ue9veloppement Arvida) de la compagnie Alcan Inc. et le CTA (Centre des technologies de l'aluminium) du CNRC m\ue8nent un effort concert\ue9 pour d\ue9velopper une version industrielle de la technologie SEED pour la fabrication de p\ue2te d'aluminium semi-solide d\ue9di\ue9e au moulage de pi\ue8ces de haute performance, principalement pour l'industrie de l'automobile. Cette technologie brevet\ue9e parAlcan Inc. est un nouveau proc\ue9d\ue9 simple et r\ue9duisant les co\ufbts de pr\ue9paration du mat\ue9riau d'alimentation des proc\ue9d\ue9s de formage. Le proc\ue9d\ue9 implique deux \ue9tapes principales : l'extraction rapide d'une quantit\ue9 contr\uf4l\ue9e de chaleur de la charge de m\ue9tal liquide afin de g\ue9n\ue9rer un m\ue9lange liquide/solide et le drainage de l'exc\ue8s du liquide laissant derri\ue8re une masse compacte, se supportant elle-m\ueame et pouvant alors \ueatre manipul\ue9e et form\ue9e sous pression. Le proc\ue9d\ue9 peut \ueatre utilis\ue9 avec une gamme \ue9tendue d'alliages d'aluminium et peut facilement \ueatre adapt\ue9 pour produire diff\ue9rents poids de lopin pour le moulage. Le transfert de chaleur joue un r\uf4le pr\ue9dominant aussi bien lors de la fabrication de la p\ue2te semi-solide que lors de la production des pi\ue8ces et son analyse est pr\ue9sent\ue9e pour ces deux aspects.NRC publication: Ye

Heat Transfer Analysis of the Swirl Enthalpy Equilbration Device for the Production of Semi-Solid Aluminum

NRC publication: Ye

Psychotic and nonpsychotic depressions: II. Platelet MAO activity, plasma catecholamines, cortisol, and specific symptoms

Preliminary data are presented on levels of plasma cortisol, dopamine (DA), epinephrine (EPI), and norepinephrine (NE) before and after dexamethasone in 22 depressed patients (of whom 4 were psychotic). Platelet monoamine oxidase (MAO) activity, determined in 19 of the depressed patients, was significantly higher in the 4 psychotic patients than it was in the 15 nonpsychotic patients. Positive correlations were observed before and after dexamethasone among cortisol, DA, EPI, and platelet MAO. After dexamethasone, plasma NE correlated negatively with DA, EPI, and cortisol. The various correlations were due largely to the inclusion of the psychotic depressive subgroup. Data are also presented on the relationships between these biological measures and specific signs and symptoms