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Constitutive behaviour of aluminum alloys AA3104, AA5182, and AA6111 at below solidus temperatures Chaudhary, Alankar

Abstract

The vertical direct chill (DC) casting process is a key production route for the fabrication of aluminum alloy sheet products. In the DC casting process, due to differential temperature, strain and strain rate conditions across the bottom and the side faces of sheet ingot, high thermal stresses are generated, that in turn can cause butt-curl, stability problems, cracking or melt bleed-outs. These ’defects’, developed during the DC casting process have been a major quality concern since the invention of DC casting in the 1930s. To predict thermal stresses developed during DC casting process and optimize the casting process, thermomechanical models have been used. Development of these thermomechanical models for DC casting of light metals requires knowledge of the constitutive behaviour of the material under thermomechanical conditions that are typical (strain rates from 1 x 10-¹s-¹ to 1 x 10-⁵ s -¹) of those experienced during DC casting. This research work reviews the thermomechanical conditions experienced during DC casting and the use of an empirical model to predict the high and low temperature constitutive behaviour of aluminum alloys in the solid state under deformation conditions relevant for DC casting. The effect of temperature, strain and strain rate has been studied for three commercially important alloys, namely: AA3104, AA5182 and AA6111. A brief study on the effect of sample orientation in the ingot has also been conducted. To determine the material parameters necessary for the extended Ludwik equation, compression tests were conducted, on industrially supplied as-cast material, using the Gleeble 3500 available at the UBC. correlations quantifying the material parameters for each alloy as a fknction of temperature were developed for each of the alloys studied. To validate the material parameters of the extended Ludwik equation, some different compression tests were performed in which specimens were deformed while they were cooled in air after heating up to ∼ 500°C. These complex thermomechanical history tests were simulated using the FE program ABAQUS where the constitutive behaviour of the materials was simulated using the extended Ludwik equation. In the complex history tests, the material experiences some recovery which is not accounted for in the extended Ludwik equation. To account for recovery, an empirical model has been suggested based on the work hardening parameter for the material.

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