Precipitation behavior and precipitates characterization of Al-Zn-Mg-Cu alloy during the non-isothermal aging process

In this work, the precipitation behavior and precipitates characterization of Al-Zn-Mg-Cu alloy during non-isothermal aging (NIA) process were investigated by transmission electron microscopy (TEM) and microhardness testing. The existence state of the overall precipitates in the alloy has been studied, and the evolution sequence can be expressed as: SSS→ GP II zones→ GPII zones and η′ precipitates→ η precipitates→ η precipitates and GPII zones→ η precipitates. The results show that the η series precipitates can provide support for the hardening of Al-Zn-Mg-Cu alloy, especially the GPII zones and η′ precipitates. Besides, some interesting phenomena were observed and explained, and a new type of η precipitate (η₁₄) was characterized.