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–35·5Cu) 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°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 α-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.