Constitutive behavior of as-cast AA1050, AA3104, and AA5182

Abstract

Recent thermomechanical modeling to calculate the stress field in industrially direct-chill (DC) castaluminum slabs has been successful, but lack of material data limits the accuracy of these calculations. Therefore, the constitutive behavior of three aluminum alloys (AA1050, AA3104, and AA5182) was determined in the as-cast condition using tensile tests at low strain rates and from room temperature to solidus temperature. The parameters of two constitutive equations, the extended Ludwik equation and a combination of the Sellars-Tegart equation with a hardening law, were determined. In order to study the effect of recovery, the constitutive behavior after prestraining at higher temperatures was also investigated. To evaluate the quantified constitutive equations, tensile tests were performed simulating the deformation and cooling history experienced by the material during casting. It is concluded that both constitutive equations perform well, but the combined hardening-Sellars-Tegart (HST) equation has temperature-independent parameters, which makes it easier to implement in a DC casting model. Further, the deformation history of the ingot should be taken into account for accurate stress calculations.

Stress–Strain Predictions of Semisolid Al-Mg-Mn Alloys During Direct Chill Casting: Effects of Microstructure and Process Variables

“…In this work, it was assumed that the liquid cannot carry any load, but instead it is carried entirely by the existing solid network. This constitutive law was refined by Haaften et al [11] by considering the critical term to be (1 À f LGB ), where f LGB is the fraction of grain boundary covered by the liquid, instead of the fraction solid, f s . A further refinement, to utilize an internal variable to represent the state of cohesion of the mush, was proposed by Ludwig et al [12] An alternative methodol-ogy for modeling semisolid deformation has been to extend the range of the so-called modified Ludwik equation up to the temperature corresponding to the fraction solid for mechanical coalescence, T coal (e.g., [8,9,13] ), and then to assume a low elastic modulus and high yield stress above this point.…”

Two-Phase Modeling of Hot Tearing in Aluminum Alloys: Applications of a Semicoupled Method

“…The effect of the coalescence of the grains at a high solid fraction is also introduced above a critical fraction g s coal of typically 96 pct in the expression of coherency C. [9] The materials parameters that appear in this model were determined by experimental identification. [9,21,22] In the case of the fully solid material (g s = 1, C = 1), this model takes a more classical form:…”

“…[22] At lower temperatures, strain-hardening effects become significant and it is thus necessary to introduce a generalized Ludwik model: [22][23][24] where the creep strain e cr can only accumulate below T e (the temperature below which strain hardening becomes significant). The strain sensitivity g and strain-rate sensitivity k are temperature-dependent functions (typically g(T) is low at high temperature and high at low temperature, while it is the opposite for k(T)).…”

Hot Tearing Susceptibility in DC‐Cast Aluminum Alloys

“…4, 12, and 13] have been developed which take into account the constitutive behavior of the material in both solid and semi-solid states. The constitutive equations used to describe material behavior in the solid include plastic-strain [14] and creep based power-law equations [15] as well as internal state variable models that includes a term for microstructure evolution [16]. The generally accepted practice is to include the effects of strain hardening and strain rate sensitivity, usually through the use of the so-called modified Ludwik equation,…”

“…In this work, it was assumed that liquid cannot carry any load, which is entirely carried by the existing solid network. This constitutive law was refined by Van Haaften et al [14] to consider the critical term to be (1-fLGB), where fLGB is the fraction of grain boundary area covered by the liquid, instead of the fraction solid, fs. A further refinement, to utilize an internal variable to represent the state of cohesion of the mush, was proposed by Ludwig et al [18].…”