Influence of grain-refiner addition on the morphology of fe-bearing intermetallics in a semi-solid processed Al-Mg-Si alloy

© The Minerals, Metals & Materials Society and ASM International 2013The three-dimensional morphologies of the Fe-bearing intermetallics in a semisolid-processed Al-Mg-Si alloy were examined after extracting the intermetallics. α -AlFeSi and β-AlFeSi are the major Fe-bearing intermetallics. Addition of Al-Ti-B grain refiner typically promotes β-AlFeSi formation. β-AlFeSi was observed with a flat, plate-like morphology with angular edges in the alloy with and without grain refiner, whereas α -AlFeSi was observed as "flower"-like morphology in the alloy with grain refiner. © 2013 The Minerals, Metals & Materials Society and ASM International

Influence of Al grain structure on Fe bearing intermetallics during DC casting of an Al-Mg-Si alloy

207 mm diameter direct chill (DC) cast billets of 6063 aluminium-magnesium-silicon (Al-Mg-Si) alloy were produced with various different primary aluminium (α-Al) grain structures including feathery-dendrites, equiaxed-dendrites and equiaxed-globular morphologies. To control the α-Al grain structure (grain morphology and grain size) an intensive shearing melt conditioning technique and Al-5Ti-1B grain refiner were used. For the first time, due to the variety of controlled microstructures produced in the DC billets, it was possible to study and determine the role of the α-Al grain structure on the iron (Fe) bearing intermetallics (Fe-IMCs). The size, shape and three dimensional (3D) inter-connectivity of the Fe-IMCs were observed to be affected by the modification of the primary α-Al grain morphology and grain size. Although both “αc-AlFeSi” and “β-AlFeSi” phases are present in all billets, β-AlFeSi phase is dominant in the billets with grain refiner addition while αc-AlFeSi is dominant in the billets without grain refiner. This suggests that the addition of Al-5Ti-1B grain refiner plays a more significant role in the intermetallic phase selection than the primary α-Al grain morphology or grain size