Corrosion Behavior of Friction Stir Welded Hpdc AM60B Lap Joints
Notice bibliographique
Résumé
Capitalizing on the potential for Mg alloys to reduce vehicle weight, a multi-national Mg-intensive front end research and development (MFERD) initiative has been established to identify and address the processing, joining and corrosion protection challenges that need to be overcome to support the fabrication of a complete Mg-intensive automotive front end assembly. The initiative identified high pressure die-cast (HPDC) AM60B and linear friction stir welding (FSW) as the preferred structural casting and joining technology, respectively, to be used for the fabrication of demonstrator sub-assemblies for component-level testing. A key fundamental aspect underpinning the successful implementation friction stir welded HPDC AM60B joints is a well-developed understanding of the extent of atmospheric corrosion damage expected to occur across the joint when boldly-exposed. The susceptibility of HPDC AM60B to localized corrosion arises from the heterogeneous microstructure and the formation of galvanic couples between the Mg matrix and the secondary intermetallic phases. Friction stir welding has been reported to significantly alter this heterogeneous microstructure across the welded joint. However definitive links between microstructure and localized corrosion susceptibility remain elusive. Electrochemical polarization and scanning vibrating probe (SVP) measurements were made to establish links between the localized corrosion susceptibility observed across the FSW joint and the resultant variations in microstructure, as revealed by scanning electron microscopy (SEM). Microstructural parameters of interest included microhardness, grain size and the size and spacial distribution of Al-Mn intermetallic particles and the secondary Mg17Al12(β) phase. The corrosive environment used was a near-neutral 5 wt.% NaCl solution. Complementary surface analyses by X-ray photoelectron spectroscopy (XPS) of the starting surface films were made to delineate the role played by the native oxide film on the subsequent localized corrosion susceptibility. The findings based on the bulk immersion testing were subsequently validated by continuous salt fog atmospheric corrosion testing. Of the microstructural parameters studied, only the grain size and spacial distribution of the secondary Mg17Al12 (β) phase were significantly affected across the friction stir welded joint. The stir zone exhibited a finer grain size relative to the unaffected base material, but did not exhibit a secondary Mg17Al12 (β) phase network. The combined set of electrochemical measurements (open-circuit potential, potentiodynamic polarization and SVP) consistently revealed that the stir zone was more susceptible to localized corrosion than the unaffected base material. SVP measurements on both the original topography and a flat-polished surface demonstrated that the stir zone striations had little effect on this tendency (see Figure 1). The findings thus far point to a combined alloy chemistry and structure link (centering on the fate of the secondary Mg17Al12 (β) phase network) between the localized corrosion susceptibility observed across the friction stir welded joint and the resultant variations in microstructure. Figure 1
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,001 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».