The effect of grain refining on the microsegregation of aluminium-magnesium alloy 5182

Aluminium alloy 5182 (AA5182) contains approximately 4.5% Mg as its princip al alloying addition, and is most commonly used to make the lid of the alum inium can. With a view to the possible future development of a micro-macro model to describe the casting of this alloy, the effect of grain refinement on the microsegregation of magnesium in industrial rolling ingots of AA518 2 has been investigated at three different depths beneath the edge of the i ngot (and hence three different cooling rates)-60, 140 and 600 rum. The acc uracy with which published microsegregation models are able to predict the solute distribution profile is assessed. It has been found that the magnesi um segregation range (C-max-C-min) of the grain refined samples actually in creases as cooling rate decreases. The range of the non grain refined sampl es is independent of cooling rate. The solute concentration profiles of the theoretical microsegregation models examined do not correlate well with th e experimentally measured profiles. It is concluded that this poor correlat ion is due to either the effect of post solidification homogenisation or th e influence of macroscopic variables during the cast. A more accurate model of post solidification homogenisation is required to assess the relative c ontribution of each of these factors to the poor correlation. In addition, it is concluded that the measurement of segregation is best done using a co mbination of EDX mapping and point analysis techniques to locate and quanti fy the areas of maximum and minimum solute concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.