Controlling the Formation of Iron-Bearing Intermetallics in Wrought Al Alloys by Melt Conditioned DC (MC-DC) Casting Technology

Abstract

With the increasing use of recycled aluminium alloys from the end-of-life products more and more iron is accumulated into the compositions of alloys. Sometimes, recycling causes the iron levels to increase beyond the set target levels for down-stream processing. The only way to deal with this impurity currently in industry is to increase the primary aluminium added to the furnace to dilute the melt and re-add all other elements or cast it for re-melting or extrude it for products that is not surface finish critical or required higher corrosion resistance. Formation of small well dispersed spherical a- or small b- Fe-bearing intermetallics, which can be homogenised for shorter times and has no negative effect on downstream processing, would be promising even if the iron levels are above the targeted compositional limits. In the present paper, fine and dispersed Fe-bearing intermetallics have been achieved by Melt Conditioned DC (MC-DC) casting technology, instead of coarser Fe-bearing intermetallics forming network like morphology in the DC castings with grain refiner additions (DC-GR). This suggests feasibility of an increased tolerance of iron levels by melt conditioned DC casting technology.