[Zurück]

T. Wojcik, A. Redermeier, T. Ebner, E. Kozeschnik:
"Characterization of metastable phases in Al-Mg-Si alloys after interrupted heating experiments";
Vortrag: Euromat 2019, Stockholm; 01.09.2019 - 05.09.2019.

Objectives
Al-Mg-Si alloys play an important role in the automotive and aerospace industry due to their outstanding mechanical properties. Many studies on industrial AW-6xxx alloys are reported in the literature. We designed two high purity alloys, in order to characterize the precipitation states, not affected by other phases and solutes. The aim of this work is the quantitative characterization of the metastable phases in these alloys.
Material and methods
Two high purity Al alloys, one with 0.37 wt-% Mg and 0.61 wt-% Si and one with 0.38 wt-% Mg and 0.22 wt-% Si were designed. In order to represent the well-known precipitation sequence of the Al-Mg-Si alloys, we use differential scanning calorimetry (DSC). We perform heat treatments at the same heating rates on a dilatometer and interrupt them at the precipitation temperatures estimated by DSC. We characterize these samples quantitatively by transmission electron microscopy (TEM). Upon the analysis of the micrographs we obtain number densities, mean dimensions, morphology and volume fractions of the precipitates.
Results
In both alloys we find states with GP-zones, β´´-, β´- and stable Mg2Si-precipitates in good agreement with the formation temperatures estimated by the DSC curves. In the higher alloyed samples, we find also Si-precipitates at high temperatures. In addition, the formation peaks of precipitates occur at lower temperatures and the volume fractions of the respective phases are higher than in the alloy with the lower Si content.
Conclusions
We present the typical precipitation sequence for AW-6xxx series on two high purity alloys. The higher Si content is the reason for the formation of Si-precipitates, the precipitation at lower temperatures and higher volume fractions of the particular phases. The results will be used to set up a parameter framework for thermo-kinetic simulations on AW-6xxx series.