Features of Microstructural and Mechanical Behavior in ECA Pressed Aluminium Alloys under High Strain Rate Superplastic Flow

Mikhail M. Myshlyaev 

Russian Academy of Sciences, Baikov Institute of Metallurgy and Material Science (IMET RAS), 49 Leninsky prospect, Moscow 119991, Russian Federation

Abstract

The structure of rods subjected to the equal-channel angular (ECA) pressing have been studied by X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, including back electron scattering diffraction and orientation image microscopy, technique. A fine-grained structure has been shown to form in the process of pressing, finer grains forming at lower pressing temperatures. A largest number of grains demonstrate the formation of a dislocation substructure involving subgrains. A most developed substructure forms under pressing at elevated temperature.

A mechanical behavior under tension has been studied for ECA pressed samples having different structural states. Temperature and strain rate conditions to attain ultimate strains to failure have been defined for samples of each structural state. It has been shown that samples with a developed substructure are subject to a superplastic (SP) straining. Contrary to the expectations the ductility of finest-grained samples turned out low.

Mechanical behaviour of the alloys under constant tensile elongation rate and constant stress tensile creep has been studied in SP conditions. Multistage of SP flow has been shown. Dependencies of the true deformation rate on temperature, the true stress and true deformation for the hardening stage and the softening stage have been established. The activation energies and the coefficients of deformation rate sensitivity of stress, which characterize these stages, have been determined. Structural behavior has been studied.

It has been established that dynamical recrystallization on sub-grain level corresponds to hardening stage and dynamic recrystallization with participation of grain boundary sliding and migration corresponds to softening stage.

 

Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium I, by Mikhail M. Myshlyaev
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-04-26 05:54
Revised:   2009-06-07 00:44