Macro-segregation in aluminium alloy sprayformed billets Original Research Article

It is generally assumed that during sprayforming the amount of micro- and macro-segregation in the sprayforms will be limited or absent because of low liquid fractions, small grain size and high cooling rate. This paper shows that macro-segregation can occur in sprayforms of Al, even when small liquid fractions are present during growth of the sprayform. This segregation occurs by an inverse mechanism, with solute-rich liquid sucked back through a solid network by solidification shrinkage. Liquid flow outwards is further enhanced by the centrifugal force produced by sprayform rotation. The liquid sucked outwards is enriched in solute (with partition coefficients <1), resulting in solute depletion at the centre and enrichment at the surface. Elements that form dispersoid particles in the spray do not segregate because they are locked into the solid network. The segregation profile can be modelled using equations similar to those used to describe inverse segregation.