Modeling of Microsegregation and Homogenization of 6xxx Al-Alloys Including Precipitation and Strengthening During Homogenization Cooling

Abstract

Control of the homogenization process is important in obtaining high extrudability and desirable properties in 6xxx aluminum alloys. Three consecutive steps of the process chain were modeled. Microsegregation arising from solidification was described with the Scheil–Gulliver model. Dissolution of Mg2Si, Si (diamond) and β-AlFeSi (β-Al5FeSi) to α-AlFeSi (α-Al12(FeMn)3Si) transformation during homogenization have been described with a CALPHAD-based multicomponent diffusion Dual-Grain Model (DGM), accounting for grain size inhomogeneity. Mg2Si precipitation and associated strengthening during homogenization cooling were modeled with the Kampmann–Wagner Numerical (KWN) precipitation framework. The DGM model indicated that the fractions of β-AlFeSi and α-AlFeSi exhibit an exact spatial and temporal correspondence during transformation. The predictions are in good agreement with experimental data. The KWN model indicated the development of a bimodal particle size distribution during homogenization cooling, arising from corresponding nucleation events. The associated strengthening, arising from solid solution and precipitation strengthening, was in good agreement with experimental results. The proposed modeling approach is a valuable tool for the prediction of microstructure evolution during the homogenization of 6xxx aluminum alloys, including the often-neglected part of homogenization cooling.

Formation of intermetallic particles during solidification and homogenisation of two Al–Mg–Si alloys

“…compositional changes of the constituents as well as the formation of dispersoids, was aided by simulations with a statistical precipitation model termed ClaNG, which relies on the Kampmann-Wagner methodology for computing nucleation, growth and dissolution of second-phase particles using multi-component thermodynamics (Ref. [40], see also [24,26,27,49]). In order to determine the microchemistry evolution along a given process chain with the ClaNG model, the underlying time/temperature profile-here the time/temperature history of the homogenisation cycles-is input into the model.…”

“…Depending on the cooling rate the microchemistry may undergo additional changes, including the formation of metastable phases of the Mg 2 Si-family and further growth of the Mn-bearing dispersoids (e.g. [26][27][28][29][30]). However, cooling of the large rolling slabs with weights of 10 tons and higher entails very low cooling rates.…”

Influence of hydrogen vacancy interactions on natural and artificial ageing of an AlMgSi alloy

“…Mg being the slowest solute, the coarsening kinetic is controlled by its mobility and the diffusion coefficient of this element will be considered ( m 2 .s -1 , and kJ.mol -1 [44,55,64]). Then, in fig.…”

Phase Field Simulation of AA6XXX Aluminium Alloys Heat Treatment

“…In both cases, for temperatures above 650 • C, the microstructure includes only the liquid phase while, during undercooling, the formation of iron-intermetallic phases has been observed at 620 • C. For the lower Si concentration (0.6 wt.%), the iron intermetallic phase has a general chemical formula of Al 8 Fe 2 Si, attributed to the general category of α-AlFeSi particles, having spherical morphology and cubic crystal structure. After the end of solidification and about the range 620-580 • C, Al 8 Fe Si will be transformed to Al 9 Fe 2 Si 2 , attributed to the general category of β-AlFeSi particles, needle-shaped, having a hexagonal crystal structure [35,36]. On the contrary, for a higher Si concentration (1.1 wt.%) the transformation α-AlFeSi to β-AlFeSi is achieved before the completion of solidification.…”