Modelling and experimental validation of microstructure evolution during the cooling stage of homogenization heat treatment of Al–Mg–Si alloys

Abstract

A CALPHAD-coupled multi-component multi-phase Kampmann-Wagner Numerical modelling framework has been adapted and coupled with a homogenization model to predict the competitive nucleation and growth of multi-sized metastable/stable phase particles during the cooling stage of a homogenization heat treatment. The reported model is the continuation of our previous work on the homogenization soaking modelling [Du et al, Acta Materialia 61 (2013) 4961-4973]. It takes the experimentally verified soaking modelling prediction results as the initial microstructural status and predicts the microstructural evolution during the very last step of the homogenization treatment, i.e. the final cooling process. The model has been applied to two Al-Mg-Si alloys: AA6061 and AA6082. The simulation shows a multi-modal MgSi particle size distribution forms due to multiple nucleation events. For the AA6082 alloy the multiple nucleation events occur mainly due to the local micro-chemistry variations along a dendrite while for AA6061 it is due to the two opposite contributions to supersaturation: the positive contribution by the cooling and the negative contribution by the particles' growth. The interaction of intergranular and intragranular MgSi containing particles have been captured, and the partitioning of Mg and Si solutes among the two different sized MgSi particles has been predicted. The model predictions are in reasonable agreement with the microstructure characterization results obtained with Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Electrical Resistivity Measurement on the quenched samples from some dedicated laboratory-scale homogenization heat treatment experiments. It is concluded that the extended KWN modelling framework is applicable to predict the microstructure evolution during the non-isothermal heat treatment of

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

“…The bi-modal nature of the PSD arises from the two nucleation events discussed above. Similar multi-modal PSD curves have been reported recently in [32] and have been attributed to multiple nucleation events, which arise from differences in local chemistry. The evolution of the volume fraction of the particles is depicted in Figure 15.…”

“…Fractions of β-AlFeSi temporarily rise until the Si (diamond) phase disappears and then plummet as α-AlFeSi grows to its equilibrium value, completely consuming the β-AlFeSi. Simultaneously, the dissolution of Mg 2 Si accelerates resulting in its disappearance shortly before β-AlFeSi at approximately 3 h. Similar trends have been reported in the experimental work in [7,10] as well as the modeling works in [25,32]. The reduction of the mole fraction of Mg 2 Si during homogenization at 560 °C is shown in Figure 6.…”

“…The complex interaction of Fe and Mn has been investigated with a diffusion model in [31]. Microstructure evolution during homogenization cooling has been modeled in [32] while a numerical model treating both homogenization holding and homogenization cooling has been presented in [33]. The aforementioned modeling approaches treat individual elements of the process chain.…”

Effect of Two-Stage Homogenization Heat Treatment on Microstructure and Mechanical Properties of AA2060 Alloy

“…The faster the cooling rate, the less the Al 2 CuLi phase precipitated. The cooling rate affected the phase precipitation, which was the same in other similar alloys [19,20].…”

Effect of Cooling Rate on Precipitation during Homogenization Cooling in Balanced Al–Mg₂Si Alloy

“…The model predictions were in good agreement with the microstructure characterization results in the AA6082 and AA6061 alloys. 8) Although homogeneous precipitation during homogenization cooling has been extensively studied in the AlMgSi alloys, the heterogeneous precipitation behavior is still unclear, especially when the precipitates nucleate on the dislocations. This work focused on the heterogeneous precipitation in the AlMgSi alloy during the homogenization cooling process.…”