Effects of solute interactions on grain refinement of commercial aluminium alloys

It is well known in the Aluminium industry that some alloys are more difficult to grain refine than others, making them more susceptible to hot cracking defects. In this paper, an analysis is presented of the effects of alloying elements, individually and collectively, on grain refinement in a series of model and commercial alloy compositions treated with 3/1 TiBAl grain refiner. Standard TP1 grain refinement data for 32 alloy systems including AA3004, AA5083, AA6063 and AA7050 [1] are evaluated in terms of the expected constitutional supercooling effect from each addition. It is shown that in most systems, simple summation of individual consitutional effects is adequate to predict the total influence on grain size of higher order systems. However, deviations from this simple behaviour occur where strong elemental interactions are known to exist. Moreover, Zr is shown to have a general poisoning effect in the range of compositions examined. Interaction coefficients among solutes are invoked to explain observed grain refining behaviour.