On the Mechanical Threshold Stress of Aluminum: Effect of the Alloying Content

Abstract

The mechanical behavior of aluminum with different alloying contents up to 1 wt percent, deformed under hot-working conditions, has been analyzed in terms of the exponential saturation equation proposed by Voce for the description of the evolution of the mechanical threshold stress, σ⁁, and the model advanced by Kocks for the description of the ratio, s(ε̇,T), between the flow stress at any strain rate and temperature and σ⁁. It has been determined that the increase in the alloying content of aluminum gives rise to an increase in the mechanical threshold stress mainly due to the effect of the solute content on the saturation stress, σ⁁s and less markedly on the athermal stress, σ⁁a. On the contrary, it has been found that the increase in the alloying content gives rise to a decrease of the Stage II or athermal work-hardening rate, θ0. Also, it has been concluded that the increase in the solute content of the material gives rise to a significant increase in the parameters ε̇K and g0 that enter into the expression of s(ε̇,T). Therefore, the dependence of the flow stress at any temperature and strain rate with the alloying content evolves from the dependence of both s(ε̇,T) and σ⁁ on solute concentration. Also, it has been found that, for the present analysis, the factor s(ε̇,T) derived from Kocks model is more satisfactory than that derived from the Follansbee and Kocks model since the latter predicts negative values of the flow stress below approximately 10 MPa, that is to say, under conditions of elevated deformation temperatures and low strain rates.