Grain morphology of as-cast wrought aluminium alloys

Two of the most important microstructural features of alloys are the grain size and the dendrite arm spacing (DAS). Both grain refinement and the DAS depend upon alloy composition through constitutional undercooling, but in different ways. Grain size tends to be related to the initial rate of development of constitutional undercooling, whilst the DAS is more related to the amount of solute build-up towards the end of the solidification process. This means that element additions that have a large effect on the grain size, e.g. Ti, have much less effect on the DAS. With examples from a range of wrought Al alloys, this paper investigates how the interaction between alloy content, grain refiner additions and cooling rate affect the grain size, DAS and the grain morphology obtained in an alloy