Abstract
Numerical modelling of the stock surface layer formation has been carried out to support simulations of the reheating and breakdown rolling of the Al-Mg-Mn aluminium alloy AA3104 using a two-high laboratory mill. The results of the experimental programme have demonstrated that the structure, morphology and the filiform corrosion susceptibility of the subsurface layer appears to be strongly dependent on both the depth of the Mg enrichment formed during reheating and redistribution of this near-surface metallic element during hot rolling. The numerical problem became effectively a matter of discrete rather then continuum numerical analysis. The applied combined finite-discrete element method merges finite element tools and techniques with discrete element-based transient dynamics, contact detection and contact interaction solutions. Linking of the modelling scales is based on transferring of the corresponding boundary conditions from the macro model to the representative cell, considered as the meso- level model. This meso- model consists of a large number of deformable bodies that interact with each other. Each individual discrete element is of a general shape and size, and can be discretised into finite elements to analyse deformability and diffusion. The transfer processes in the thin surface layer are described by the system of diffusion and the motion equations for particles integrated in time. The numerical analysis indicated that, under the rolling conditions, the redistribution of Mg content can arise mainly due to one or a few of the following reasons, namely: by removal of some of the thin oxide layer by abrasion and adhesion to the work roll surface; by intermixing of the small oxides (Mg) into the subsurface layer of a few microns depth; and by diffusion. Further analysis should be carried out to validate the modelling approach and to establish the predominant mechanisms of the surface layer formation and influence of the key hot rolling parameters.