High-temperature deformation of solution-treated Al-0.6% Si-1% Mn-0.7 Fe alloy

Abstract

The tensile properties of Al-0.6% Si-1% Mn-0.7% Fe alloy were investigated in the temperature range 295–773 K, to assess the effect of the precipitation of Si, Mn and Fe during ageing and deformation on the mechanical properties. The alloy showed a pronounced drop in ductility at elevated temperatures. Elongation-to-fracture versus temperature-of-deformation curves are evaluated as a function of the strain rate. The elevated-temperature yield and ultimate tensile strength (UTS), ductility, strain-rate sensitivity and strain-hardening exponent have a strain-rate dependence. The minimum in the strain-rate sensitivity versus temperature curve is coincident with the elongation minimum temperature. At low and high temperature ranges the flow could be represented by the constitutive equations σ = K ₂ εⁿ and σ = K ₃ ε^m, respectively. There is also a discussion of the activation energy for deformation in the vicinity of the ductility minima and from plotting the logarithm of the strain rate versus the reciprocal absolute temperature at a constant yield strength (18 MN m⁻²). A tentative model based on the diffusion of Si, Fe and Mn in Al and the subsequent precipitation of Si, FeAl₃, MnAl₆ and α-Al₁₂Mn₃Si is postulated to explain the loss in ductility at high temperatures and the corresponding change in strength. An attempt is made to correlate strength, ductility and structural changes at elevated temperatures.