Investigation of precipitation behavior and related hardening in AA 7055 aluminum alloy

The precipitation behavior and related hardening in AA 7055 aluminum alloy aged at 120 and 160 °C was investigated in detail. GPI zones were the dominant phase in the alloy upon ageing at 120 °C for 60 min. The metastable η′ phase begins to precipitate in the alloy after being aged at 120 °C for 60 min, and turns to be the main phase after ageing for 300 min. When the alloy was aged at 160 °C, the precipitation was significantly promoted. The results also revealed that the transformation of small GPI zone to η′ phase is the dominant mechanism for η′ formation. Formation and growth of GPI zones and η′ phases led to the increase of the yield strength, while formation and coarsening of η resulted in the decrease of the strength. η′ is responsible for the peak hardening of this alloy.