Microstructure of Al-Zn-Mg-Cu-Zr-0.5Er alloy under as-cast and homogenization conditions

The billets of Al-Zn-Mg-Cu-Zr and Al-Zn-Mg-Cu-Zr-0.5Er alloys were prepared by semi-continuous direct chill casting (DCC). The effects of trace Er on microstructure of Al-Zn-Mg-Cu-Zr alloy under as-cast and homogenization conditions were studied. The results show that the grain morphology is large dendritic structure and the grain size increases obviously by the addition of 0.5% Er. Moreover, most of Er element in the alloy segregates at grain boundary during solidification, resulting in ternary Al8Cu4Er phase. After homogenization, most of the MgZn2 phase at grain boundary has dissolved back to Al matrix in the two alloys. In the Er-containing alloy, the dissolution temperature of Al8Cu4Er phase is about 575 °C. Therefore, the homogenization treatment cannot eliminate Al8Cu4Er phase validity.