Effect of primary intermetallic particles on surface microstructure and appearance of aluminium extrusions

Different amounts of coarse intermetallic particles were produced in an aluminium alloy by variations of the iron content. Microstructural examination of the extrusion surface shows that Fe-rich intermetallic particles reduce the grain size, randomize the texture, retard the recrystallization process and decrease the difference in the fraction of high-angle grain boundaries. After alkaline etching, the primary intermetallic particles decrease the surface gloss and its variation on the same extrusion surface, reducing the tendency for streaking defects.