Effects of creep-aging parameters on aging precipitates of a two-stage creep-aged Al-Zn-Mg-Cu alloy under the extra compressive stress

Two-stage creep-aging characteristics of an Al-Zn-Mg-Cu alloy under the extra compressive stress are investigated. The effects of the second-stage creep-aging temperature (SSCAT) and compressive stress on precipitates are discussed. It is found that the main precipitates are η′ and η phases in the two-stage creep-aged alloy. With the increase of SSCAT, the size of intragranular aging precipitates (IAPs) rapidly increases, while its density decreases. Meanwhile, the density of IAPs first increases and then decreases with the increase of compressive stress. Additionally, the grain boundary precipitates (GBPs) discontinuously distribute on grain boundaries. The size of GBPs and the width of precipitate free zones (PFZs) increase with increasing the SSCAT, and the total volume of GBPs increases with the increase of compressive stress. Moreover, the sizes of IAPs under compressive stress are bigger than those under tensile stress, while their density is relatively smaller. Furthermore, the compressive stress can effectively inhibit the growth of GBPs and the broadening of PFZs. Compared with the creep-aged alloys under tensile stress, the sizes of the GBPs are smaller, and the PFZs is narrower in the creep-aged alloys under compressive stress.