High Temperature Deformation Behavior of 8090 Al-Li Alloy

Woo Young Jung,Tae Kwon Ha

doi:10.1155/2013/512606

Abstract

High temperature deformation behavior, especially the superplasticity of an 8090 Al-Li alloy, was studied within the recent framework of the internal variable theory of structural superplasticity. In this study, a series of load relaxation tests were conducted at various temperatures ranging from 200°C to 530°C to obtain the flow curves of log ε˙versus log ε. The effect of grain size was also examined by varying the grain sizes through a proper thermomechanical treatment. The flow curves were found to be composite curves consisting of contributions from grain boundary sliding (GBS) and grain matrix deformation (GMD) at superplastic temperatures. The activation energy obtained for GMD was 124.9 kJ/mole in the temperature range from 470°C to 530°C, very similar to that for self-diffusion in pure Al.

Highlights

IntroductionThe strain rate sensitivity parameter, m, can be defined as the slope of the log σ versus log εcurves
The high temperature deformation behavior, including superplasticity, of crystalline materials has generally been described phenomenologically by a power-law relation between the two external variables, namely, flow stress (σ) and strain rate (ε)̇, as follows [1, 2]: σ = Bεṁ, (1)where B is a constant
The relaxation test results obtained at various temperatures are shown in Figure 4 for the specimens with the average grain size of 50 μm

Summary

Introduction

The strain rate sensitivity parameter, m, can be defined as the slope of the log σ versus log εcurves This parameter has widely been used as one of the most important parameters characterizing the superplastic deformation behavior [1,2,3]. The value of m is, observed to vary continuously along the log σ versus log εcurves, unable to provide a critical value above which superplastic deformation can be predicted [4]. When it comes to structural superplasticity (SSP), it is apparent that the external or phenomenological variables such as σ, ε, and εalone cannot adequately describe SSP. Superplastic properties are exhibited in materials having a stable, equiaxed, and extremely fine microstructure only under a very narrow range of strain rate and temperature normally above 0.5TM, where TM is an absolute melting temperature [3]

Methods

Results

Discussion

Conclusion