Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties, electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated. The results indicated that with elevating the aging temperature from 100°C to 160°C, the aging response rate was greatly accelerated, and the UTS at peak aging condition decreased, while the corresponding TYS increased. However, the electrical conductivity of the alloy became higher. After aging for 24 h at 120°C, the peak UTS and TYS values were achieved as 591 MPa and 541 MPa, respectively; but the alloy achieved a lower conductivity, 20.4 MS/m. When T6 temper was performed at 140°C for 14 h, the UTS decreased only by 1% of the former, whereas the TYS and the electrical conductivity increased obviously, which were up to 559 MPa and 22.6 MS/m, respectively. The major strengthening precipitates of the peak-aged alloy were GP zones and η′ phase. The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature. There were obvious PFZs along the grain boundary both in T6 conditions aged at 140°C and 160°C. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2008AA03Z506)