Pore closure in thick aluminum plate: From industrial hot rolling to individual pore observation

Pores are often present in large aluminum ingots after casting. To ensure the mechanical reliability of the final thick plates, these pores must be closed during the forming process, hot rolling in the present case. This study aims at understanding the effects of rolling parameters on the volume evolution of pores. To do so, X-ray microtomography is used to track real casting pores during deformation. Nevertheless, thick plates are too large to enable a fine characterization of the evolution of pores during the process. The size and shape of the samples as well as the mechanical boundary conditions must be optimized to meet imaging constraints. This paper focuses on the reproduction of complex loading paths. Multi-scale FE simulations are used to reproduce the loading conditions of thick plate rolling with uniaxial tests on samples of a few millimeters. Uniaxial tests are then characterized with tomography on a synchrotron X-ray beamline. In each sample, tens of pores are individually tracked, giving access to their volume evolution. The local loading path experienced by each pore is determined with FE simulation. It is shown that the volume evolution of a real pore correlates with the hydrostatic inte-gration which is the integral of stress triaxiality along cumulated strain. This confirms that the closure of complex casting pores is enhanced by a high relative reduction and high values of L/H ratio during rolling similarly to what was observed numerically on simpler shapes.

Automated summary

This study investigates the volume evolution of pores during the rolling process of thick plates using X-ray microtomography. Multi-scale finite element simulations are used to replicate the loading conditions, and tomography on a synchrotron X-ray beamline is employed for characterization. The results show that the volume evolution of pores is closely related to the hydrostatic integration, confirming the enhanced closure effect of complex casting pores with high relative reduction and high L/H ratio during rolling.