Impact of crystallographic texture orientation and its spatial distribution on mechanical performance of Al alloys for automotive – modeling approach

Key words: FE simulations, Crystal plasticity, EBSD, roping, bending of automotive sheets

Context:

Due to its low density, aluminium (Al) is a key material for sustainability as it allows lightweighting. To decrease the CO2 emissions associated with its production, it is required to massively use recycled aluminium, meaning remelting Al scrap to make new ingots. However, switching from primary synthesis (bauxite reduction) to secondary synthesis (scrap melting) often leads to increasing impurities, the main one being iron in aluminium. Such contaminants may impact the performance of the current alloys in terms of ductility/formability,. It is the case for the hemming of automotive outer panels. The latter are bent around the inner part after stamping to ensure mechanical assembly. The project of the internship is linked to microstructure optimization, and especially crystallographic texture (meaning grain orientations and their spatial arrangement) to mitigate the detrimental effects of impurities. Thus, it is key to identify how grain microstructure could be tuned to maintain current product performance, while increasing recycled content. For that, Constellium C-TEC has integrated within its modeling tools an open-source software, Damask, allowing to model the mechanical behavior of grains aggregates under different loading types, including tension and bending. A model combining Finite Element Modeling (FEM) and Crystal Plasticity (Damask) has been developed. Up to now, the simulations are performed on a Representative Volume Element (RVE) of the material (hundreds of microns size) which is built with two constraints: mean grain size and grain orientations. No spatial position and size is imposed for each texture component.

Objective:

The main topic of this internship is to model explicitly a spatial distribution of orientations, using experimental data coming from EBSD (Electron BackScatter Diffraction), DCT (Diffraction Contrast Tomography) and XRD (X-ray diffraction) measurements to understand how this spatial distribution can impact the mechanical response of the material, both the plastic anisotropy (yield surface) and the strain localization during loading. . Tensile loading will be a first case of application, particularly relevant for surface defects appearing during stamping (roping). And the model will then be extended to the more complex case of bending.

The project has several components:

The role of the intern will consist, after a first phase of training in our trades and tools, to do:

Literature review on methods to transpose microstructure measurements to numerical spatially arranged RVE
X-Ray diffraction (XRD) measurements to measure global crystallographic texture, together with Electron Backscatter Diffraction (EBSD) to assess spatial arrangement of grain orientations.
Building of a numerical twin of the microstructure to be loaded within Damask software and FEM software (Marc)
Handling of the existing numerical models: mainly tensile and bending ones. Some minor changes may be brought by the intern.
Study of the impact of spatial arrangement on surface plasticity prediction, strain localization in tension (roping defect) and bending.
Comparison between simulations and experiments for identifying which type of texture should be promoted to enhance performance.
Analysis and synthesis of the results, report writing and presentation to the team.

At C-TEC, the intern will be part of an R&D team of engineers with expertise in metallurgy and mechanics and will be in relation with partners handling the experimental aspects of the investigations. Interaction with an academic expert of crystal plasticity (SIMaP laboratory) is part of the project.

Education level:

Engineering school of Master of Science ideally in Material Science or Mechanics of Materials

Competencies & technical & soft skills requirement: