On the assumption of an additive effect of solute elements in dendrite growth

The individual effect of some common alloying elements on the dendrite growth conditions in aluminium—silicon casting alloys has been investigated by measuring the dendrite coherency point. In the existing theories for dendrite growth it is usually assumed that the effect of the solute elements is additive, and one purpose of the present investigation is therefore to investigate this approach. The effect of successive additions of Mg, Fe and two levels of grain refinement, by AlTi5Bl, on dendrite coherency has been investigated in two AlSi alloys; AlSi7 and AlSi11. By changing the order of addition of these elements, the assumption of an additive effect is verified. The results show that two separate parameters are altered with the alloying additions: the grain size and the dendrite growth rate, both being very important for the solidification characteristics. When the effect on grain size is considered separately, there is a good qualitative correspondence between the theoretical predictions and the experimental results.