Mechanical behavior of aluminum deformed under hot-working conditions

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The stress-strain behavior of aluminum 3–9 purity deformed at elevated temperatures has been analyzed on a rational basis. Emphasis has been given to the analysis of the curves corresponding to typical deformation conditions of interest for hot rolling of commercial aluminum alloys. The strainhardening behavior has been modeled assuming the validity of the typical saturation exponential equation earlier proposed by Voce. The temperature and strain dependence of the flow stress parameters involved in such an equation has been introduced by means of a model based on the power law relationship, where the stress-sensitivity exponent of the strain rate is considered to be temperature dependent. The strong temperature dependence of this parameter precluded the use of the exponential relationship expressed in terms of the Zener-Hollomon parameter. Therefore, a different temperature-compensated strain rate parameter similar to the MacGregor-Fisher parameter has been employed following the earlier developments put forward by Kocks. Thus, a satisfactory correlation of the flow stress parameters with the deformation conditions has been obtained. The final constitutive equation derived provides a satisfactory reproduction of the experimental values of the flow stress and follows quite closely the strain-hardening behavior. The mean activation energy determined by the different models confirmed the predominance of both climb of edge dislocation segments and motion of jogged screw dislocations as the rate-controlling mechanisms during deformation of this material under hot-working conditions. The use of a constitutive equation which expresses the flow stress of the material in terms of the applied strain, rate of straining, and deformation temperature to calculate the power dissipation efficiency of the material(η) deformed under hot-rolling conditions has shown that it could be strongly strain dependent, particularly toward the end of the rolling schedule. Hence, it has been concluded that the calculation of both the power co-content as defined in dynamic material modeling (DMM) and its maximum value, taking into consideration the constitutive equation previously developed, represents a more plausible and soundly based approach toward the determination of η.