Abstract:Four alloy rods of Al-Zn-Mg-Cu-Zr-xEr (x=0, 0.1, 0.2, 0.5, wt%) were prepared by directional solidification. The microstructure and second phase morphology of alloys were investigated by optical microscopy (OM), electron probe micro-analysis (EPMA), energy dispersive spectrometer (EDS) and other methods. The results indicate that Er element can increase the number of dendrites in the directional solidification structure of Al-Zn-Mg-Cu-Zr alloy, and reduce the primary dendrite arm spacing and secondary dendrite arm spacing of the alloy. A proper amount of Er element can reduce the content of second phase in the alloy and increase the tendency to form round second phase. The formation of Al8Cu4Er phase can reduce the Cu content in the T phase (AlZnMgCu phase), which plays a role of rounding the boundary of the T phase, and can change the morphology and internal structure of the T phase. The Al8Cu4Er phase serves as the nucleation position of the T phase, and part of the T phase grows around this phase. The addition of Er can improve the microhardness of the alloy.