Comportement en fatigue de l'aluminium 357 coulé par gravité et rhéocoulé.
Bibliographic record
Abstract
RESUME Le moulage est un procede de mise en forme qui permet de produire rapidement et a bas prix des pieces d’aluminium de geometries complexes. Cependant, les pieces moulees de facon conventionnelle contiennent des defauts qui nuisent a leur resistance en fatigue. Pour cette raison, le matricage et l’usinage sont generalement utilises pour produire des pieces structurales critiques en aluminium. Le moulage semi-solide est un procede a mi-chemin entre le moulage liquide et le matricage. En developpement depuis les annees soixante-dix, ce procede permet d’ameliorer la qualite metallurgique des pieces de fonderie. Le principal avantage du moulage semi-solide (MSS) est de reduire la contraction a la solidification puisque la gelee injectee dans les moules est partiellement solide. Les pieces produites par MSS contiennent normalement moins de retassures que les pieces moulees a l’etat liquide. De plus, la microstructure de ces pieces est globulaire ce qui les distingue des pieces moulees a l’etat liquide qui possedent une microstructure dendritique. Les resultats issus de la bibliographie montrent que le rheomoulage et le thixomoulage ont des avantages sur les plans mecanique et economique. L’allongement a la rupture et la resistance en fatigue d’un materiau mise en forme par MSS sont normalement plus grands que ceux du meme alliage mise en forme par moulage en coquille (MC). Toutefois, le ou les parametres microstructuraux qui influencent la resistance en fatigue des pieces produites par MSS n’ont pas encore ete identifie(s). Le but premier de ce travail est donc d’expliquer la difference de resistance en fatigue entre un materiau moule en coquille et rheomoule sur la base de leurs differences microstructurales. Le travail experimental a ete realise sur l’alliage d’aluminium 357 produit en six materiaux de microstructures differentes. Cet alliage a ete choisi puisqu’il est couramment utilise dans l’industrie pour produire des pieces d’automobiles et d’aeronefs et il se rheomoule facilement. De plus, cet alliage a ete principalement utilise pour developper la technologie SEED. D’abord, une quantification des parametres microstructuraux et des proprietes mecaniques des materiaux a ete effectuee. Cela a confirme que les materiaux rheomoules ont une microstructure globulaire. Les resultats montrent aussi une augmentation de la limite d’elasticite de l’alliage attribuable au rheomoulage. Toutefois, des quatre materiaux rheomoules, seuls ceux ayant subi une modification de leur structure eutectique ont un allongement a la rupture superieur a celui des----------ABSTRACT Casting is a forming process used for rapid and low cost production of aluminum parts of complex geometries. However, conventionally cast parts contain defects that are detrimental to their fatigue strength. For this reason, forging and machining are generally used to produce safety critical aluminum components. Semi-solid molding is a process that can be considered to be half way between liquid casting and solid forging. In development since the seventies, this process is able to improve the metallurgical quality of cast components. The main advantage of semi-solid molding (SSM) is a reduction of the shrinkage during solidification since the material is already partially solid. Components produced by SSM normally contain fewer shrinkage cavities than components cast from the liquid state. Moreover, the microstructure of these components is globular as opposed to components cast in the liquid state that are characterized by a dendritic microstructure. Results found in the literature show that rheomolding and thixocasting have both mechanical and economical advantages. The elongation at fracture and the fatigue resistance of a material produced by SSM are generally higher than those of the same alloy produced by liquid casting in a permanent mold (PM). However, the microstructural parameter influencing the fatigue resistance of SSM components have not yet been identified. The primary objective of this work is to explain the fatigue strength difference between a permanent mold and a rheomolded material on the basis of the microstructural differences. The experimental work has been carried out using aluminum 357 alloy which was produced in six specimens characterized by different microstructures. This alloy was chosen because it is frequently used in the industry to produce automotive and aerospace components and because it is easy to rheomold. Also, this alloy has been widely used to develop the SEED technology. First, the microstructural characteristics and mechanical properties of the materials were quantified. This confirmed that the SSM materials have a globular microstructure. The results also showed an increase of the yield strength attributed to rheomolding. However, among the four SSM materials, only those for which the eutectic structure was modified had higher elongation at fracture than the permanent mold materials. The highest measured elongation at fracture is 19 % obtained for the modified SSM material, tested in the as-cast condition. The other materials tested all have an elongation at fracture below 10 %. For both shaping process, results show that
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.003 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".