Microstructure Development in Undercooled Al-Al2Cu Alloys.

摘要

Following nucleation, microstructure development is dictated by competitive growth kinetics and heat flow. For the Aluminum-AL2CU eutectic, a lamellar morphology is observed over wide ranges of solidification rate. However, in powders cooled at 0.25-5.00 C/S and at undercooling from 40 to118 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. % Cooper showing coupled eutectic growth at the highest undercoolings. 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. Keywords: Aluminum alloy; Recalescence; Thermal analysis; Powder alloys; Reprints. (AW)