Modification of microstructures for hypoeutectic, eutectic and hypereutectic Al-Cu binary alloys

Al-Cu alloys of compositions near eutectic point [hypoeutectic (Al-19Cu), eutectic (Al-33Cu) and hypereutectic (Al-35 center dot 5Cu) and (Al-36Cu)] were chemically modified by adding 0.6 wt-% Al-Ti5-B1 master alloy. In addition, the specimens of unmodified and chemically modified eutectic alloy were heat treated at 500 degrees C for different holding times (4, 24, 48 and 72 h for the unmodified and 4 and 29 h for the modified ones) followed by water quenching. The structure of chemically treated alloy was changed from large dendrites to fine rosette shaped alpha-Al grains inside fine eutectic matrix. For these alloys, the liquid-solid transformation temperature was shifted to a higher value. The addition of Al-Ti5-B1 master alloy to the eutectic (Al-33Cu) alloy transforms it into hypoeutectic one of fine lamellar eutectic structure. The chemically treated hypereutectic alloy (Al-35% 5Cu) was changed into full eutectic alloy.