Analysis on the amplitude of serrated flow associated with the Portevin-LeChatelier effect of substitutional fcc alloys

The serration of flow curve is a common feature of the Portevin-LeChatelier effect of substitutional fee alloys. Under the condition that the onset strain of serration decreases with increasing temperature, previous experimental results have shown that the serration stress amplitude, Δσ-, increases with increasing strain (ε) and temperature (T); it decreases with increasing grain size (d) and strain rate (ε). A conventional rationalization assumes that Δσ is proportional to the number of solute atoms, N, in dislocation atmospheres, where N is a function of the diffusion coefficient, aging time, and temperature. By adopting this approach and taking into account the effects of strain rate, strain, and grain size, the relation Δ7sigma; ∝ [ε^-1 ε^{β(1/2 + γ)} d^{-n(1/2 + γ)} T^-1 exp (-Q/kT)]^2/3 is proposed, where Q is the activation energy associated with substitutional diffusion. The proposed model fits well with the experimental data of an Al-3.7 wt pet Mg alloy.