Following nucleation, microstructure development is dictated by competitive growth kinetics and heat flow. For the AlAl 2Cu eutectic, a lamellar morphology is observed over wide ranges of solidification rate. However, in powders cooled at 0.25–500°C −1 s −1 and at undercoolings from 40 to 118°C, a two-zone morphology develops where zone A is an irregular eutectic structure and zone B is lamellar. These structures have been examined as a function of composition, undercooling and cooling rate. A symmetric coupled zone was found, with alloys of 27.5–40 wt.% Cu showing coupled eutectic growth at the highest under coolings. These results indicate that the applied cooling rate affects the zone B lamellar spacing which is considered to be controlled by heat flow, and the scale of the irregular zone A morphology at a constant level of undercooling.