Microstructural evolution in DC cast aluminum alloy Al-6.3Zn-2.3Mg-2.2Cu-0.1Zr ingot during homogenization and subsequent cooling

Microstructure of post-homogenization is significant to prevent particle stimulated nucleation of recrystallization during hot deformation. This paper investigated microstructure evolution in an Al-6.3Zn-2.3Mg-2.2Cu-0.10Zr alloy during homogenization and subsequent cooling. The as-cast microstructure of Al-6.3Zn-2.3Mg-2.2Cu-0.10Zr alloy consists of α-aluminum dendrite with complex inter-metallic compounds segregated into the inter-dendritic regions. The main inter-metallic compounds formed during casting were MgZn2, Al2CuMg, Al7Cu2Fe and Mg2Si. After homogenization, the dendrite network disappeared completely, the MgZn2 and Al2CuMg phases were dissolved into the Al matrix. Two intermetallic phases, Al7Cu2Fe and Mg2Si were insoluble during homogenization. After homogenization and cooling to 400°C followed by quenching, precipitates nucleated discontinuously on the grain boundaries, no precipitates was found within the grains. The precipitates were found near the grain boundaries when quenching from 350°C, and the precipitates uniformly distributed within the center of the grains when quenching from 250°C.