Flow stress anisotropy in aluminium
Abstract
The plastic anisotropy of cold-rolled high purity aluminum (99.996%) and commercially pure aluminum (99.6%) has been investigated. Sample parameters were the initial grain size and the degree of plastic strain (ϵ < 3.00). Flow stresses (0.2% offset) were measured at room temperature by uniaxial tension as a function of the angle between the tensile axis and the rolling direction. Textures were determined by neutron diffraction, and Taylor M-factors were calculated. The microstructures were studied by TEM. It was found that the flow stress varies significantly with orientation both at low and high strains. It is shown that for most experimental conditions, texture effects alone cannot explain the observed anisotropy, and microstructural anisotropy effects have to be taken into account. In those cases, a correlation between the microstructural anisotropy and the development of microbands is discussed.
Résumé
On a étudié l'anisotropie plastique d'aluminiums laminés de haute pureté (99,996%) et de pureté commerciale (99,6%). Les paramètres de l'échantillon sont la taille de grains initiale et le taux de déformation plastique (ϵ < 3,00). Les contraintes d'écoulement (à 0,2%) sont mesurées à la température ambiante en tension uniaxiale, en fonction de l'angle entre l'axe de traction et la direction de laminage. Les textures ont été déterminées par diffraction neutronique et les facteurs M de Taylor ont été calculés. Les microstructures ont été étudiées par MET. La contrainte d'écoulement varie de façon significative avec l'orientation à la fois pour les faibles et pour les fortes déformations. Pour la plupart des conditions expérimentales, les effets de texture seuls ne peuvent pas expliquer l'anisotropie que l'on observe, et l'on doit tenir compte des effets de l'anisotropie microstructurale. Dans ces cas là, on discute une corrélation entre l'anisotropie microstructurale et le développement de microbandes.
Zusammenfassung
Die plastische Anisotropie kaltgewalzten hochreinen (99,996%) und kommerziell reinen (99,6%) Aluminiums wurde untersucht. Als Probenparameter dienten die anfängliche Korngröβe und der Grad der plastischen Dehnung (ϵ < 3,00). Die Flieβspannungen (bei 0,2%) wurden bei Raumtemperatur unter einachsigem Zug in Abhängigkeit von dem Winkel zwischen der Zugachse und der Walzrichtung gemessen. Die Texturen wurden mittels Neutronenbeugung ermittelt; die Taylor-Faktoren wurden berechnet. Die Mikrostruktur wurde im Elektronenmikroskop untersucht. Die Flieβspannung ändert sich mit der Orientierung sowohl bei niedrigen wie auch hohen Dehnungen beträchtlich. Unter den meisten experimentellen Bedingungen können die Textureinflüsse die beobachtete Anisotropie nicht erklären, e müssen Effekte der Mikrostruktur berücksichtigt werden. Für diese Fälle werden die Zusammenhänge zwischen der Anisotropie der Mikrostruktur und der Entwicklung von Mikrobändern diskutiert.
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