Flow localization and neck formation in a superplastic metal

doi:10.1016/0001-6160(81)90133-4

Acta Metallurgica

Volume 29, Issue 5, May 1981, Pages 911-920

https://doi.org/10.1016/0001-6160(81)90133-4 Get rights and content

Abstract

Experiments were conducted on the superplastic Zn22% Al eutectoid alloy to investigate the extent of flow localization and neck formation in the three regions of plastic flow. The results show that the behavior is qualitatively similar in the low stress region I and the high stress region III, but there are very significant differences in the superplastic region II.

Deformation is essentially uniform in region II up to at least ~800% and quasi-uniform thereafter, whereas there are marked deviations from uniform flow in regions I and III at ~200%. Failure occurs by the formation and catastrophic growth of a sharp neck in regions I and III, whereas necking is diffuse at high elongations in region II. The results are consistent with a genuine decrease in the value of the strain rate sensitivity at low strain rates in region I.

Résumé

Nous avons étudié expérimentalement la localisation de l'écoulement et la formation de la striction dans les trois domaines d'écoulement plastique d'un alliage eutectoïde superplastique Zn-22% Al. Nos résultats montrent des comportements qualitativement semblables dans la région I des faibles contraintes et dans la région III des fortes contraintes, mais des différences très significatives dans le domaine superplastique II.

La déformation est essentiellement uniforme dans le domaine II jusqu'à au moins 800% environ et quasi-uniforme ensuite, alors qu'il y a des déviations très nettes par rapport à un écoulement uniforme dans les domaines I et II pour 200% environ. La rupture dans les domaines I et III se produit par formation et croissance catastrophique d'une striction très franche, alors que la striction est diffuse dans le domaine II pour les grands allongements. Nos résultats sont cohérents avec véritable diminution de la sensibilité à la vitesse de déformation pour les faibles vitesses de déformation dans le domaine I.

Zusammenfassung

An der superplastischen eutektoiden Legierung Zn22% Al wurde das Ausmaβ der Gleitlokalisierung und der Einschnürungsbildung in den drei plastischen Bereichen untersucht. Die Ergebnisse zeigen, daβ das Verhalten im Bereich I niedriger Spannung und im Bereich III hoher Spannung qualitativ ähnlich ist. Dagegen treten erhebliche Unterschiede im superplastischen Bereich II auf. Die Verformung läuft im Bereich II bis zu mindestens ~ 800% stetig, darüber quasistetig ab. Dagegen treten in Bereich I und III bei ~ 200% beträchtliche Abweichungen vom stetigen Flieβen auf. In Bereich I und III entsteht der Bruch durch Bildung und katastrophales Wachstum einer scharfen Einschnürung; dagegen ist die Einschnürung im Bereich II bei groβen Verlängerungen diffus. Die Ergebnisse sind verträglich mit einem echten Abfall in der Dehngeschwindigkeitsempfindlichkeit bei kleinen Dehngeschwindigkeiten im Bereich I.

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Flow localization and neck formation in a superplastic metal

Abstract

Résumé

Zusammenfassung

Acta metall.

Acta metall.

Acta metall.

Scripta metall.

Scripta metall.

Scripta metall.

Acta metall.

Acta metall.

Scripta metall.

Acta metall.

J. appl. Phys.

Rate Processes in Plastic Deformation of Materials

Metall. Trans. A