A Model of the β-AlFeSi to α-Al(FeMn)Si Transformation in Al-Mg-Si Alloys

Abstract

During the homogenisation process of Al-Mg-Si extrusion alloys, plate-like -Al 5 FeSi particles transform to multiple roundedAl 12 (FeMn) 3 Si particles. The rate of this to transformation determines the time which is required to homogenise the aluminium sufficiently for extrusion. In this paper, a finite element approach is presented which model the development of fraction transformed with time, in the beginning of the transformation, as a function of homogenisation temperature, as-cast microstructure and concentration of alloying elements. We treat the to transformation mathematically as a Stefan problem, where the concentration and the position of the moving boundaries of the and particles are determined. For the boundary conditions of the model thermodynamic calculations are used (Thermo-Calc). The influence of several process parameters on the modelled transformed fraction, such as the temperature and initial thickness of the plates, are investigated. Finally the model is validated with experimental data.

Evolution of Fe Bearing Intermetallics During DC Casting and Homogenization of an Al-Mg-Si Al Alloy

“…Kuijpers et al [11] suggested this transformation is solute diffusion controlled, initiated by the a c -AlFeSi nucleation on the basal face of b-AlFeSi platelets; the b-AlFeSi then dissolves and a c -AlFeSi grows by consuming released Fe, Mn and Si. They also observed an increase in Mn content in a c -AlFeSi particles after homogenization due to longer diffusion times.…”

“…[6] Therefore, a post-cast homogenization heat treatment is used commercially to encourage transformation of b to a to allow: (a) more reliable downstream deformation, typically by extrusion, (b) improved mechanical properties, especially toughness and elongation to failure, and (c) improved surface finish. [5,[10][11][12][13][14][15][16] Despite the apparent maturity of AA6xxx alloys, there is a significant on-going effort to optimize homogenization conditions in terms of properties, while also minimizing the homogenization time. Among the factors that govern the homogenization response, the initial cast microstructure and the alloy chemical composition play key roles.…”

Mechanical properties of Al–Mg–Si alloy sheets produced using asymmetric cryorolling and ageing treatment

“…Either because of an intrinsic brittleness or because of a lack of coherence with the matrix, these particles will result in a damage initiation owing to the nucleation of small internal voids, which develop into cracks when exposed to stresses [38,39]. The plate-like particles can lead to a crack initiation and induce surface defects in the deformed material [42]. In these sheets, it is possible that the deformation of Fe-Cr-Mn-Si particles results in some micro-defects in sheets with increasing the number of passes, as shown in Fig.…”

Heat Transfer Model for Thin Solidified Material in Continuous Casting

“…implicit) direct numerical approach, e.g. the finite difference method (FDM), 9,10) the finite element method (FEM), 11) or the boundary element method (BEM) 12) is necessary for the TSMP. For this approach, a significantly large calculation cost is inevitable because a rather small time increment compared with the required casting time is necessary; the time increment is limited by the Courant-Friedrich-Levy (CFL) condition, which governs the calculation stability and accuracy, even in an implicit method because of the special limitation for solidification analysis.…”