Development of a Rheological Model of Hot Deformation as Exemplified by 1424 and В-1461 Aluminum Lithium Alloys

Abstract

A variant of a rheological model of hot deformation is proposed: the law of hyperbolic sine, which, as opposed to standard law, accounts not only for the rate of deformation and temperature of the process, but also the degree of deformation. The material constants in the law of hyperbolic sine are substituted with polynomial functions of the degree of deformation; its coefficients are calculated using a specially developed procedure. The proposed rheological model has been applied for aluminum lithium alloys of lower density, grade 1424, Al–Mg–Li–Zn system, and grade V-1461, system Al–Cu–Li–Zn, for which, using physical simulation at the Gleeble-3800 facility, the flow curves were determined in the temperature range of 400–480°C and the rates of deformation of 1–60 s–1 to the degree of deformation of 0.6. In addition, the influence of the initial state of the material is studied: samples are taken both from the ingot and from hot rolled plates. The constants of the rheological model of hot deformation, including the Zener–Hollomon parameter and the law of hyperbolic sine for the overall range of stresses and deformations, are determined. After approximating the parameters of this model as a function of real deformations using the polynomial law of the 4th order, the rheological model was developed describing the behavior of an alloy in the considered range of temperatures and rates. The parameters of the law of hyperbolic sine are determined as a function of degree of deformation. It is demonstrated that the parameters for a cast material are higher than for a rolled material. A comparison of the standard model with the proposed one demonstrated that the use of a standard model gives overestimated flow stresses in the entire deformation range (up to 12%).