Precipitation Behavior, Recrystallization Behavior, and Mechanical Properties of Highly Alloyed Al-Zn-Mg-Cu Alloy with Respect to Zn/Mg Ratio

In this work, the precipitation behavior and recrystallization behavior of highly alloyed Al-Zn-Mg-Cu alloy with different Zn/Mg ratio were investigated using optical microscope, scanning electron microscope, X-ray diffraction, transmission electron microscope and tensile test. The results indicated that the primary phase increases with Zn/Mg ratio dropping, which increases the nucleation particles and refines the grains. The real solidification path is between Lever law and Scheil model, which is closer to Scheil model. The precipitates are η′ when Zn/Mg ≥ 4.19 in T6 temper. However, it is the co-precipitation of η' and T' when Zn/Mg < 4.19 and the fraction of η' decreases from 100 to 7.6% as Zn/Mg ratio decrease from 4.19 to 1.91. In addition, the impact of residual eutectic phase in a low Zn/Mg ratio alloy on recrystallization behavior and mechanical properties was discussed. Grain boundary primary phases in low Zn/Mg alloys are difficult to completely dissolve during the solid solution. Interestingly, the particle stimulated nucleation occurs preferentially around the second phase and gradually extends to the center of the grain, and there are still low angle grain boundaries in the center of larger original grain. When Zn/Mg > 1.91, the tensile strength increases with Zn/Mg ratio dropping. After Zn/Mg ≤ 1.91, the tensile strength decreases slightly due to the residual second phase. Graphical Abstract