Abstract
Abstract In this article, a new age-hardening model for Al-Mg-Si alloys is presented (named NaMo-Version 2), which takes into account the combined effect of cold deformation and prolonged room-temperature storage on the subsequent response to artificial aging. As a starting point, the original physical framework of NaMo-Version 1 is revived and used as a basis for the extension. This is permissible, since a more in-depth analysis of the underlying particle-dislocation interactions confirms previous expectations that the simplifying assumption of spherical precipitates is not crucial for the final outcome of the calculations, provided that the yield strength model is calibrated against experimental data. At the same time, the implementation of the Kampmann–Wagner formalism means that the different microstructure models can be linked together in a manner that enforces solute partitioning and competition between the different hardening phases which form during aging (e.g., clusters, β″ and β′). In a calibrated form, NaMo-Version 2 exhibits a high degree of predictive power, as documented by comparison with experiments, using both dedicated nanostructure and yield strength data as a basis for the validation. Hence, the model is deemed to be well-suited for simulation of thermomechanical processing of Al-Mg-Si alloys involving cold-working operations like sheet forming and stretch bending in combination with heat treatment and welding.
Highlights
A natural aging model based on the Kampmann–Wagner formalism is deemed to be the best choice in the present context, since such a model would be fully compatible with the other nanostructure model (NaMo) models and easy to implement into the existing mathematical framework
The main conclusions to be drawn from the development and testing of NaMo-Version 2 can be summarized as follows: In general, simulation of thermomechanical processing of Al-Mg-Si alloys involving cold-working operations like sheet forming and stretch bending in combination with heat treatment and welding requires the use of an age-hardening model which takes into account the combined effect of cold deformation and prolonged room-temperature storage on the subsequent artificial aging response
The important reactions contributing to the nanostructure evolution during natural aging, cold deformation, and artificial aging are first identified and implemented, either in the existing NaMo sub-models, or in new ones
Summary
THE age-hardening Al-Mg-Si alloys achieve their unique mechanical properties through a delicate balance of precipitation hardening, solid solution hardening, and strain hardening.[1,2,3] Because the former strength contribution is by far the most important one, the precipitation sequence and resulting strength evolution occurring during natural and artificial aging of the alloys have been extensively investigated and reported upon in the scientific literature.[4,5,6] In addition, the chemical composition and atomic structure of the clusters and hardening precipitate which form have been studied in detail by means of various high-resolution experimental techniques along with atomistic modeling.[7,8,9,10] Obviously, some of these works must be said. At any time during the artificial aging process, the resulting stress-strain curve at RT can be calculated from the integrated yield strength and work-hardening models for different thermomechanical treatments and alloy compositions and used in more advanced numerical analyses of the mechanical integrity of real aluminum structures.[22,23,24,25,26,27,29,30]. In the following, both the new and the adapted models being implemented in NaMo-Version 2 will be described more in detail. The applicability of NaMo-Version 2 in illuminating the interplay between the different process variables involved will be illustrated in a dedicated case study
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