On the precipitation mechanisms of β-Mg2Si during continuous heating of AA6061
Robert Kahlenberg, Tomasz Wójcik, Georg Falkinger, Anna Lena Krejci, Benjamin Milkereit, Ernst Kozeschnik
Abstract
In the present work, we study the evolution of metastable and Cu-containing precursor precipitates into stable β-Mg2Si using in-situ transmission electron microscopy during continuous heating of an AA6061 aluminum alloy. The experiments indicate that the transformation into stable β-Mg2Si involves the release of Al and Cu atoms into the matrix phase combined with the rearrangement of Mg and Si at the interfaces. Nucleation of the β-Mg2Si precipitates predominantly occurs at the interface between the precursors and the aluminum matrix and at dispersoids. The term precipitate-related transformation is used to emphasize the reaction mechanism, where a new product precipitate nucleates next to a precursor and consumes it at its original location predominantly via interface diffusion. The in-situ investigations are complemented by an analysis of bulk samples and a comparison with differential scanning calorimetry measurements, which show excellent agreement.