Microstructure and Intermetallic Phase Evolution during the Homogenization of an Al-Zn-Mg-Cu-Zr-Nd Aluminum Alloy

The intermetallic phase evolution during the homogenization of an Al-Zn-Mg-Cu-Zr alloy with Nd addition is investigated. Large amounts of the eutectic interdendritic acicular-state eta (MgZn2) phase, primary phase T (AlZnMgCu), Al8Cu4Nd, and Al7Cu2Fe exist at the grain boundaries of the as-cast Al-Zn-Mg-Cu-Zr-Nd alloy. The homogenized intermetallic phase evolves as follows: the eta phase dissolves into the alpha (Al) matrix, most of the T phase is dissolved in 16 h, and the remaining part of the T phase is transformed into the S phase (Al2CuMg) after 24 h. The stable Al8Cu4Nd phase in the alloy captures Cu atoms and inhibits the further generation of the S phase during homogenization. The addition of Nd decreases the fraction of the S phase, and only Al7Cu2Fe, Al8Cu4Nd, and Al2CuMg remain after homogenization for 24 h. Homogenization kinetics analysis suggests that the Al-Zn-Mg-Cu-Zr-Nd alloy is suitably homogenized at 470 degrees C 24 h(-1).