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.
Highlights
The process chain of extrudable 6xxx aluminum alloys consists of a series of individual elements including melting and alloying, direct-chill casting in billets, homogenization, extrusion and aging
Microsegregation during solidification, dissolution of Mg2Si, Si and β-AlFeSi (βprecipitation and associated strengthening during homogenization cooling have been modeled with a CALPHAD-based multicomponent diffusion model and the Kampmann–Wagner Numerical precipitation and associated strengthening during homogenization cooling have been modeled with (KWN) precipitation framework
Mg2 Si precipitation and associated strengthening during homogenization cooling have been modeled with a CALPHAD-based multicomponent diffusion model and the Kampmann–Wagner Numerical (KWN) precipitation framework
Summary
The process chain of extrudable 6xxx aluminum alloys consists of a series of individual elements including melting and alloying, direct-chill casting in billets, homogenization, extrusion and aging. These effects can be partially or completely eliminated with the application of a suitable homogenization treatment The benefits of this treatment include the following: removal of elemental microsegregation, dissolution of low-melting eutectics, transformation of iron-containing intermetallic compounds, shape control (round-off) of hard particles with sharp edges, dissolution of the grain-boundary Mg2 Si phase, and re-precipitation with a more homogeneous in-grain distribution during homogenization cooling. All these effects improve the extrudability and increase the response of the material to natural or artificial aging [5]. The proposed modeling approach treats three consecutive elements of the process chain i.e. microsegregation during solidification, homogenization and homogenization cooling, in an effort to provide insight into the effect of as-cast grain size inhomogeneity as well as precipitation and associated strengthening during homogenization cooling
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