The effect of beta, beta ' and beta '' precipitates in a homogenised AA6063 alloy on the hot deformability and the peak hardness

The effect of beta'-, beta"-, and beta Mg-Si precipitates in the initial mi crostructure of an AA6063 alloy on the flow stress at elevated temperatures was studied using plane strain compression tests. The stress-strain curves were modelled with a general solute-dependent constitutive equation based on the exponential saturation equation as proposed by Sah and the hyperboli c sine law. The solute content during testing was estimated using a finite- volume based numerical code for particle dissolution. It was found that in the experimental regime investigated, beta" precipitates in the initial mic rostructure have no significant effect on the flow stress and peak hardness . Furthermore beta' precipitates in the initial microstructure increase the flow stress at 673 K and decrease the corresponding peak hardness, but do not influence the flow stress at 773 K and corresponding peak hardness. The presence of beta precipitates results in a significant reduction of the fl ow stress and the peak hardness by reducing the solute content during defor mation. Taking into account the solute content Calculated with the finite-v olume model, the stress-strain curves can be modelled successfully with onl y one set of parameters for a range of pre-treatments. (C) 2001 Elsevier Sc ience B.V. All rights reserved.