Characterization of the α-Al(FeMn)Si nuclei on β-AlFeSi intermetallics by laser scanning confocal microscopy

As-cast billets of aluminum extrusion alloys of the 6xxx Al alloys family require a homogenization treatment to make the material suitable for hot extrusion. During this homogenization treatment several processes take place such as the transformation of interconnected plate-like monoclinic beta-Al5FeSi intermetallics into more rounded discrete cubic alpha-Al sub 12(FeMn)3Si particles, the dissolution of Mg2Si and Si precipitates and the precipitation of elements still in supersaturated state. Of these processes the phase transformation of the intermetallics and the accompanying shape change is deemed to be the most important for obtaining a good extrudability and in particular a good surface quality in the extruded product. However, little microstructural and topological information is available concerning the details of this transformation process and in the absence of such information realistic modelling of the kinetics of this transformation on a physical basis is not possible. To enable the construction of such physical models quantitative information concerning the position of the alpha particles on the beta plates, their 3D shape during early and later stages of growth, and their site density is required.