Creep aging properties variation and microstructure evolution for 2195 Al–Li alloys with various loading rates

Abstract

Creep age forming (CAF) technology has been successfully applied to the manufacture of large aluminum alloy components. As the component size is large, the loading rate of different parts of the component has a large deviation. In order to fully understand the CAF process of large components, the effects of loading rate on creep aging (CA) treatment of Al–Li alloy were investigated at 180 °C for 18 h, including the deformation, mechanical properties, and microstructure evolution. Compared with different loading rates (2 N/s, 1 N/s and 0.5 N/s) in the CA experiment, the loading rate can be found to effectively affect the CA behavior of the materials. On the one hand, higher loading rate (2 N/s) is beneficial to the accumulation of creep strain in the process of CA, the increase of loading rate will cause the creep strain to increase suddenly. On the other hand, the increase of loading rate will promote the nucleation of T1 phase, refine the precipitate, limit the precipitation of θ′ phase, shorten the peak-aged time, reduce the peak aging strength and increase the elongation. In addition, the increase of loading rate also promotes the transition from brittle fracture to mixed fracture. The evolution of microstructure during aging was observed by transmission electron microscope (TEM). It is confirmed that the effect of loading rate on creep behavior is mainly caused by the change of dislocation due to the difference of loading rate, which leads to the change of evolution law of precipitated phase. Moreover, the mechanism of material properties and creep strain change is explained.