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 (alpha-Al) grain structures including feathery-dendrites, equiaxed-dendrites and equiaxed-globular morphologies. To control the alpha-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 alpha-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 alpha-Al grain morphology and grain size. Although both alpha(c)-lFeSi and beta-AlFeSi phases are present in all billets beta-AlFeSi phase is dominant in the billets with grain refiner addition while alpha(c)-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 alpha-Al grain morphology or grain size. (C)16 Elsevier Inc All rights reserved.